Unit 4 Human Biology Flashcards
(205 cards)
1
Q
Restriction Enzymes
A
Because DNA molecules are very long, often consisting of millions of base pairs, restriction enzymes cut the DNA at specific points to make smaller fragments known as restriction fragments.
- The fragments can be separated using gel electrophoresis & recombinant DNA.
- Particular repeat sequences can be cut out by restriction enzymes:
— Short tandem repeats (STRs).
— Restriction fragment length polymorphism (RFLPs).
— Variable number tandem repeats (VNTRs).
2
Q
STRs, RFLPs, VNTRs
A
- ≥90% of DNA does not carry nucleotide triplets that code for proteins.
- Some of the non coding regions (introns) consist of repeated sequences of nucleotides.
- The number of repetitions in any one section of DNA varies from one individual to the next.
3
Q
Short Tandem Repeats
A
- Occurs wen a pattern of two or more nucleotides is repeated & the repeated sequences are adjacent to each other.
- Pattern can range in length from 2 to 10 base pairs.
- Typically non-coding intron region.
- Count of repeats of a specific STR at a given locus can create unique genetic profile.
- Currently over 100 000 published STR sequences in human genome.
- Prevalent method for determining genetic profiles in forensic cases.
- Analysis is performed by extracting nuclear DNA from cells of interest.
- DNA is amplified using PCR.
- Tested by gel electrophoresis or capillary electrophoresis.
- Applications: forensics (crime, mass disaster, paternity testing, military DNA ‘dog tag’, convicted criminal DNA databases), bone marrow transplant follow-up (important for establishing graft rejection & disease relapse).
4
Q
Variable Number Tandem Repeats
A
- These can be found on many chromosomes & often show variation in length - the repeat number may vary from 1 - 30 repeats of 8 - 50 base pairs.
- Each variant acts as an inherited allele allowing use for identification.
- These repeat regions are usually bounded by specific restriction enzyme sites.
5
Q
Restriction Fragment Length Polymorphism
A
- Variation in the DNA sequence of a genome detected by breaking DNA into pieces with restriction enzymes.
- Analyse fragments by gel electrophoresis.
- Important tool in genome mapping, localisation of genetic disease genes, determination of risk for a disease, genetic fingerprinting & paternity testing.
- Applications: agriculture (direct method for selecting desirable genes such as disease resistance), forensics, genetic mapping (determine disease status of an individual (eg. Huntington’s disease, cholera), cystic fibrosis, sickle cell anaemia), genetic counselling.
6
Q
STR
A
Short tandem repeat
7
Q
RFLP
A
Restriction fragment length polymorphism
8
Q
VNTR
A
Variable number tandem repeats
9
Q
Steps in DNA Identification
A
- Isolate DNA & make copes (PCR).
- Cut the DNA into shorter fragments that contain STRs (using restriction enzymes).
- Sort the DNA by size (gel electrophoresis).
- Compare samples to identify a person.
10
Q
PCR
A
- Polymerase Chain Reaction
- Can produce many copes of a specific target segment of DNA.
- Three step cycle - denaturing (heating), annealing (cooling), extension (replication) - that brings about a chain reaction that produces an exponentially growing population of identical DNA molecules.
- Can copy different lengths of DNA, it does not have to copy the whole length of a DNA molecule:
→ One gene
→ Several genes
→ Lots of genes - Artificial process which imitates natural DNA replication.
11
Q
Reagents Needed for PCR
A
- DNA sample which is wanted to be replicated.
- Taq DNA Polymerase - enzyme that works at high temperatures.
- Nucleotides (called dNTPs).
- Pair of primers
→ One primer binds to the 5’ end of one of the DNA strands.
→ The other primer binds to the 3’ end of the other anti-parallel DNA strand.
→ Delineate the region of DNA that is to be amplified.
12
Q
PCR Steps
A
- Denaturing: heated to 92ºC briefly to separate strands by breaking H-bonds.
- Annealing: cooled to 55ºC to allow primers to form H-bond with ends of target sequence.
- Extension: heated to 72ºC, DNA polymerase adds nucleotide bases from the 3’ end of each primer.
13
Q
Gel Electrophoresis
A
- The different sized fragments are separated by a process called gel electrophoresis.
- The separation takes place in a sheet of a firm but jelly-like substance (a ‘gel’).
- Samples of the DNA extracts are placed in shallow cavities (‘wells’) cut into one end of the gel (in the negative end).
- A voltage is applied to opposite ends of the gel.
- DNA has a negative charge & moves slowly towards the positive end.
- The shorter fragments travel through the gel faster than the longer fragments, creating ‘lanes’.
14
Q
Genetic Fingerprinting
A
- DNA analysis can be sued for catching criminals, establishing parentage, finding how closely organisms are related & many other applications.
- The pattern of bands in a gel electrophoresis is known as a genetic fingerprint or a ‘genetic profile’.
- If a genetic fingerprint in a sample of blood or other tissue at the scene of a crime matches the genetic fingerprint of a suspect, this can be used as evidence.
- A DNA sample can be obtained from the suspect using blood, check epithelial cells taken from the mouth lining of even the cells clinging to the root of a hair.
15
Q
DNA Sequencing
A
- Modified nucleotides called dideoxyribonucleotides (ddNTPs) attach to synthesised DNA strands of different lengths.
- Each type of ddNTP is tagged with a distinct fluorescent label that identifies the nucleotide at the end of each DNA fragment.
- The DNA sequence can be read from the resulting spectrogram.
- Can only sequence 750 base pairs at a time.
- Genome must be broken up into sections.
- Done a number of times with overlapping pieces.
- Overlapping sections analysed & put back together.
16
Q
Analysing Gene Expression
A
- Nucleic acid probes can hybridise with mRNAs transcribed from a gene.
- Probes can be used o identify where or when a gene is transcribed in an organism.
17
Q
Studying Expression of Single Genes
A
- Changes in the expression of a gene during embryonic development can be tested using:
→ Northern blotting.
→ Reverse transcriptase-polymerase chain reaction. - Both methods are used to compare mRNA from different developmental stages.
18
Q
Northern Blotting
A
Combines gel electrophoresis of mRNA, followed by hybridisation with a probe on a membrane.
19
Q
Reverse Transcriptase-Polymerase Chain Reaction
A
- Reverse transcriptase is added to mRNA to make cDNA, which serves as a template for PCR amplification of the gene of interest.
- The products are run on a gel & the mRNA of interest identified.
- Quicker & more sensitive.
20
Q
Recombinant DNA
A
DNA produced by combining DNA from different sources.
21
Q
Vectors
A
In DNA cloning, the plasmid/chromosome used to carry the cloned DNA segment to a desired location (frequently a virus or liposome is used).
22
Q
Restriction Enzyme
A
Enzyme that cuts DNA at a specific sequence of nucleotides.
23
Q
Gel Electrophoresis
A
Procedure used to separate & analyse DNA fragments by placing a mixture of DNA fragments at one end of a porous gel & applying an electrical voltage to the gel.
24
Q
PCR Definition
A
Technique that allows molecular biologists to make many copes of a particular gene.
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Plasmid
A circular DNA molecule found in bacteria.
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Cloning
Process of making a genetically identical organism.
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Transgenic Organism
An organism that contains genes from another organism.
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Recombinant DNA Process
1. Plasmid isolated with RE.
2. DNA isolated with RE.
3. Gene inserted into plasmid.
4. Plasmid put back into bacterial cell.
5. Cell multiplies with gene of interest.
6. Copies made of gene, cell & protein.
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Cutting & Sticking
- Recombinant DNA made by cutting DNA & sticking it together. REs from bacteria cut DNA at specific points.
- REs cut DNA at the restriction site on the DNA.
- REs cut leaves some exposed single strand bases known as a ‘sticky’ end.
- Recombinant DNA made by cutting DNA & sticking it back together.
- Separate fragments of DNA joined into plasmid by enzyme DNA ligase.
- Both pieces of DNA but must have been cut by the same RE so that the sticky ends are complementary.
- The DNA is now called recombinant DNA.
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Bacterial Cells & Plasmids
- Plasmids cut with restriction enzyme used to isolate the chosen gene.
- Complimentary sticky ends formed.
- Plasmid & gene mixed & they combine.
- Plasmid then seals & forms recombinant plasmid with help of ligase enzyme.
- Plasmids mixed with bacterial cells which take up plasmid.
- Less than 1% of bacteria take up the plasmid & they are now known as transformed bacteria/transgenic bacteria (changed genes).
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Examining the Colonies
Three types of colony form:
- Bacteria that did not take up the plasmid.
- Bacteria containing a plasmid that did not seal in a copy of the DNA.
- Bacteria containing the new recombinant plasmid known as transformed bacteria.
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Identifying Transformed Bacteria
- Original plasmids have antibiotic resistance gene (used as a genetic marker) for the antibiotics ampicillin & tetracycline.
- Plasmids cut in the middle of the tetracycline gene & insulin gene inserted means there is no longer any resistance to tetracycline.
- Bacteria then grown on agar plates.
- Then transferred onto plates treated with ampicillin to see if they have the plasmid & will grow.
- Then some transferred onto plates treated with tetracycline to see if they still grow or not. If they do not, the contain the insulin gene.
- This is called replica plating.
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Medical Applications of Recombinant DNA
- Production of pharmaceuticals for treatment of diseases (eg. human insulin, interferons).
- Production of pharmaceuticals for disease prevention (eg. vaccine (hepatitis B vaccine)).
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Examples of Genetic Engineering
- If a person has T1 diabetes & cannot produce insulin, it is possible through genetic engineering to add the insulin gene to the body, so the person can produce insulin.
- The first human protein made commercially suing engineered bacteria was human insulin, but many other hormones & proteins are now being produced. In addition, many recombinant vaccines have been produced.
- Many human proteins that were formerly extremely expensive to produce because they were found in human tissues only in small amounts can now be made in large amounts from cloned genes.
- Many recombinant vaccines have been produced. These include live recombinant, vector, subunit & DNA vaccines.
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Gene Therapy
- Viruses are often sued because they have the ability to enter a cell’s DNA.
- The virus particles are modified so that they cannot cause a disease. Then a DNA fragment containing a replacement gene is spliced to the viral DNA.
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Somatic Cell Gene Therapy
- Certain genes switched on & off in differentiated cells.
- Augmentation: adding functioning genes into the relevant specialised cells meaning that the protein can be made & the cell will function normally.
- Killing specific cells: making cancer cell express genes producing proteins that make their cells vulnerable to attack by the immune system for targeted cancer treatments.
- Artificially replace the disease-causing gene with a normal allele.
- The normal allele can be carried by a virus vector to the target tissues (eg. treatment for cystic fibrosis).
- The patient is the infected with T he modified virus particles, which should carry the gene into cells to correct the genetic defects.
- Unfortunately, these experiments have not been very successful.
- Gene therapy remains a high-risk, experimental procedure.
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Germline Gene Therapy
- Stem cells that could become any type of cell or a new human being.
- Germline therapy is changing the genes of the first few cels meaning that the organisms are different.
- Somatic cell therapy is changing genes on part of the body, however the disease can still be inherited as the gene still exists in every body cell & gametes.
- Germline gene therapy is altering the organisms genes before development into a foetus, however this is illegal in humans due to:
- Potential for creation of new diseases.
- Human evolution would be interfered with.
- Too many ethical & moral issues with changing a human genome.
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Issues: Somatic Gene Therapy
- Getting genes into target cells is difficult.
- Treatment if short-lived & has to be repeated.
- Difficult to get the gene functioning in the genome.
- Only the actual patient is affected.
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Issues: Germ Line Gene Therapy
- More straightforward to deliver gene into cell.
- All subsequent cells will have the functioning gene.
- Considered unethical.
- Genetic manipulation passed on to children - could be a good or bad thing.
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Cloning
- A member of a population of genetically identical cells produced from a single cell.
- Researchers hope that cloning will enable them to make copies of transgenic animals to help save endangered species.
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Clonal Propogation
- A source of tissue or organ for transplantation.
- Avoids all problems of immunoincompatibility.
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Sickle-Cell Anaemia: Identifying
Replaces GAG with GTG at the MstII site.
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Transforming Bacteria
- When organisms contain genes from another species, they are called transgenic.
- Transgenic bacteria now produce important substances useful for health & industry.
- These transformed bacteria produce proteins cheaply, quickly & abundantly.
- Eg: human insulin, clotting factor for people with haemophilia.
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Pharming
- Animals used to create/reproduce a human gene which can be isolated and used for human use.
- Transgenic sheep used to carry a gene for a human blood protein, which they secrete in their milk. This protein inhibits an enzyme that contributes to lung damage in patients with cystic fibrosis, emphysema & other chronic respiratory diseases.
- Golden rice: transgenic rice produces beta carotene (used in human bodies to make Vit. A) that gives the rice its golden colour & their increased nutritional value. Vit. A deficiency can lead to blindness & infection.
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Xenotransplantation
- 60% transplant patients die on transplant list.
- We can now consider xenotransplantation - transplantation from other species.
- Pigs have been genetically engineered so they do not produce an enzyme involved in organ rejection.
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Xenotransplantation Problems
- Different organ size.
- Pigs only live to 15 years, so organs may age quickly.
- Pigs’ body temperature is 39ºC, whereas ours is 37ºC.
- Animal welfare groups think killing animals for organisms is wrong.
- Certain religious groups cannot eat pork, so could not have transplants.
- Possible disease transfer between animals & humans.
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Genetic Engineering: Risks & Ethical Concerns
- Risk to researcher - using crippled strains.
- Possible ecological damage from pollen transfer between GM & wild crops - superweeds.
- Pollen from a transgenic variety of corn that contains a pesticide may stunt or kill monarch caterpillars.
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Human Genome Project: Risks & Ethical Concerns
- How can we be sure that a transferred gene makes the appropriate amount of a protein & is expressed at the right time/place.
- What do we reserve gene therapy for - serious diseases, athletic enhancement, appearance, intelligence?
- Reduced genetic diversity.
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Summary of Applications of DNA Technology
- Medicine: bacteria produce human proteins.
- To identify people.
- To diagnose genetic diseases.
- To find & identify all of the human genes.
- Gene therapy.
- Genetically engineered goods.
- Agriculture: bacteria that decompose nitrogen faster, disease & pest resistant plants, bigger, sweeter, more nutritious plants, bigger, leaner animals.
- Industry: bacteria used to break down pollutants.
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Mutations: Genetics Overview
- DNA = deoxyribonucleic acid.
- DNA carries the instructions for making all the structures & materials the body needs to function - in particular, proteins.
- A chromosome consists of segments of DNA known as genes.
- Genes contain the instructions for the construction of a particular protein.
- It is estimated that there are about 20 000 - 25 000 genes in the human genome (about 3 bn base pairs).
- The sequence of bases in a gene is a code instructing the cell how to construct a particular protein.
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Modes of Inheritance
- Dominant alleles cover or override the effect of an alternative form of a gene (allele).
- Capital used to indicate the allele.
- Recessive alleles are not expressed unless there are two, one on each homologous chromosome.
- Use a lower case letter to indicate the allele.
- Homozygous (purebred): the individual has the same alleles for a particular allele pair (tt or TT).
- Heterozygous (hybrid): the individual has different alleles for an allele pair (Tt).
- Genotype is the genes an individual has (TT/Tt/tt).
- Phenotype is the observed physical expression of the allele of the observed characteristic.
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Co-Dominant Inheritance
- Where two alleles are equally dominant.
- A third phenotype is produced.
- Eg. sickle cell anaemia.
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Sickle Cell Anaemia
- Haemoglobin S is produced in large amounts.
- This causes RBCs to become distorted in shape, reducing their oxygen carrying capacity & decreasing their ability to travel through capillaries.
- This results in capillary blockage & damage to the area.
- RBCs with haemoglobin S have an average life of 16 days.
- Results in anaemia.
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Sex-Linked Inheritance
- The allele for a specific trait is carried on the X-chromosome.
- Males cannot be carriers of the trait.
- These traits show up more frequently in the male population.
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Multi-Allelic Inheritance
- Instead of two alleles for a trait, there are ≥3.
- Human blood types are multi-allelic & co-dominant.
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Polygenic Inheritance
- Polygenic traits are determined by more than one pair of genes.
- Polygenic phenotypes exhibit continuous variation, since each different gene permutation results in just a small phenotypic change.
- Many medical conditions such as autism, cancer & T2 diabetes are polygenic.
- Often continuous traits.
- Responsible for many phenotypic traits.
- Eg. skin pigmentation, height, intelligence, stature.
- These traits all results from the interaction of the genes with environmental factors.
- Many traits such as height, shape, weight, colour & metabolic rate are governed by the cumulative effects of many genes.
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Gene Expression & Environment (Skin Pigmentation)
- Results from the pigment, melanin, which occurs mainly in the skin & hair follicles.
- Melanin is produced in organelles called melanosomes, which occur in melanocyte cells in the basal layer of the epidermis.
- Melanosomes are transferred to keratinocytes (the principal cell type in the epidermis).
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Skin Colour
Depends on:
- Rate of melanin synthesis.
- Relative amounts of brown-black pigments & red-yellow pigments.
- Number & size of melanosomes.
- Rate of transfer of melanosomes from the melanocytes to the keratinocytes.
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Tanning Reaction
- Ultra violet (UV) radiation in sunlight can cause severe damage to the DNA in the skin & underlying tissues.
- Melanin acts like a natural sunscreen & protects the tissues from UV damage.
- When exposed to UV, melanocytes are simulated to produce more melanin. This is often referred to as the tanning reaction.
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Regulation of Pigmentation
- The regulation of pigmentation is very complex - more than 120 genes have been identified.
- When keratinocytes are exposed to the sun’s rays, they produce melanocyte stimulating hormone (MSH).
- MSH stimulates receptors on the surface of melanocytes, causing them to produce more melanin.
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Chromatin
- The DNA associated with proteins (histone S) that form chromosomes.
- It appears as dark-staining, granular material in the cell nucleus.
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Epigenetics
- Epi = on/over.
- Epigenetics = on/over the genetic code.
- Inheritable by dividing cells.
- The changes in gene expression that do not involve changes in the cell’s DNA but can be passed on from generation to generation.
- Epigenetic events explain the observation that cells with the same genotype can have more than one phenotype.
- Epigenetic events generally act like an on/off switch, either silencing or activating a specific gene affecting a protein production.
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Histones
- It is estimated that every cell nucleus contains 2-3m of DNA.
- To prevent the very fine strands of DNA becoming tangled, the filaments are coiled around special proteins called histones.
- As well as organising DNA, histones also affect gene expression.
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Epigenetic Mechanisms
- Knowledge of epigenetic mechanisms is still developing.
- DNA methylation, histone modification & prion proteins are all known to have important epigenetic effects.
- Epigenetic processes accumulate during a person’s life.
- Epigenetic processes are believed to be important in the development of cancer & in the differentiation of embryonic tissues.
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DNA Methylation
Methyl tags attached to DNA bases repress gene expression (‘silence’ genes).
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Histone Modification
Molecules attached to the histone tail alters the activity of the DNA wrapped around them.
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Changes to Epigenome
→ Nutrition
- Shortages or excesses of food during adolescence leads to risk of obesity, diabetes & early puberty.
- During times of famine, the P-generation may have an epigenetic shift where their needs for certain nutrients are increased.
- If this is passed to their offspring, in time of surplus, the F1 may become overly nourished & develop health risks.
- This also occurs if the P generation is overly-nourished & their offspring then live in famine. They would be less likely to handle smaller portions.
→ Parenting
- Mother rats that infrequently groom & nurse their pups rear anxious offspring.
- This alters genes controlling the production of stress hormone.
- Nature’s way of preparing young for a potentially dangerous environment.
- Fathers affect epigenome as well.
- Crop fungicide vinclozolin can cause susceptibility to cancer & kidney defects.
- Mice fed with cocaine passed on memory failure to three generations.
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Cancer Epigenetics
- Originally thought that methylation in cancer was an epiphenomenon, meaning that it was random & arose after the cancer did, not playing a role in the formation of cancerous cells.
- Differed from general genetics:
— Reversible
— Position effects (acts over larger distances than intended).
— High frequencies of mutations.
- Gene silencing: essentially turning on & off genes.
- Hypermethylation leads to silencing of tumour suppressor genes.
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Jumping Genes
- Transposons (also known as ‘jumping genes’ or transposable genetic elements) are discrete pieces of DNA that can move around to different sites along a chromosome.
- A large proportion of the human genome consists of transposons.
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Transposing Mechanisms
- Several types of transposons have been discovered.
- Some use a direct ‘cut & paste’ mechanism (top diagram).
- Others are first coped to RNA & then back to DNA before being inserted into a new location (reverse transcription or retrotransposon mechanism) (lower diagram).
- Transposons can act as mutagens - they can alter gene expression. They can often activate or disable a gene but sometimes have no observable effect.
- Some transposons resemble retroviruses (viruses such as those responsible for AIDS & certain cancers) & may even be derived from them.
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Prions
- Infectious protein.
- Normal body proteins that get converted into an alternate configuration by contact with other prion proteins.
- They have no DNA or RNA.
- The main protein involved in human & mammalian prion diseases is called ‘PrP’.
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Prion Diseases
- Prions form insoluble deposits in the brain.
- Causes neurons to rapidly degenerate.
- Mad cow disease (eg. bovine spongiform encephalitis: BSE)
- People for New Guinea used to suffer from kuru, which they got from eating the brains of their enemies.
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Allele Frequency: Gene Pool
A gene pool is the sum of total genes, with all their variations, possessed by a particular species in a particular place at a particular time.
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Changes in Gene Pool
The allele frequency in a population’s gene pool can be affected by evolutionary mechanisms, such as natural selection, or by change occurrences, such as founder effect & random genetic drift (RGD).
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Mutations
- A permanent structural alteration in an organism’s DNA that has never been seen previously in ancestors.
- An process by which the base pair sequence of a DNA molecule is altered.
- An important source of genetic variation.
- In most cases, DNA changes either have no effect or cause harm, but occasionally can improve an organism’s chance of surviving.
- Mutations in reproductive cells can be passed on to an organism’s descendants.
- Mutation rate: the number of mutations occurring or estimated to occur per generation or per nucleotide pair.
- Somatic mutation: mutation occurs but is not passed on to the next generation.
- Germ line mutation: mutation occurs in gametes & is passed to the next generation, in both its somatic & germ line cells.
- Without mutations, there would be no new alleles, new genes or evolution.
- Three main types: deletion (section of chromosome is deleted), duplication (section of chromosome is duplicated) or inversion (section of chromosome is inserted upside-down).
- Many human conditions result from genetic mutations.
- Some, such as sickle cell trait, are beneficial in some situations, whereas others, such as cancer, can be lethal.
- Natural selection determines which mutations remain in a gene pool & which ones are eliminated.
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Natural Selection (Gene Pools)
- Determines which mutations remain in a gene pool & which ones are eliminated.
- Provides a ‘plausible’ explanation for evolution.
- Scientific theory proposed by Charles Darwin & Alfred Wallace that organisms best adapted to their environment tend to survive & out-multiply those that are less well adapted.
- The allele frequency is the relative frequency of a particular allele in a population. This ranges from 0 to 100%.
- NS affects the frequency of the alleles in a population’s gene pool. The frequency of alleles determining favourable features increases & the frequency of the alleles determining unfavourable features decreases.
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Natural Selection (Gene Pools)
- Determines which mutations remain in a gene pool & which ones are eliminated.
- Provides a ‘plausible’ explanation for evolution.
- Scientific theory proposed by Charles Darwin & Alfred Wallace that organisms best adapted to their environment tend to survive & out-multiply those that are less well adapted.
- The allele frequency is the relative frequency of a particular allele in a population. This ranges from 0 to 100%.
- NS affects the frequency of the alleles in a population’s gene pool. The frequency of alleles determining favourable features increases & the frequency of the alleles determining unfavourable features decreases.
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Population Size: Large
- Individuals make only a small contribution to the gene pool.
- Evolution occurs slowly.
- Most changes are adaptive.
- NS is the main driving force.
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Population Size: Small
- Individuals make up a relatively large contribution to the gene pool.
- Evolution can occur rapidly.
- Many changes are non-adaptive.
- Many changes are due to chance events.
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Artificial Selection
- The selective breeding of domesticated plants & animals for a particular trait by man.
- Results with variety within a species.
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Terms: Macroevolution
The origin of taxonomic groups higher than the species level.
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Terms: Microevolution
A change in a population’s gene pool over successive generations.
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Terms: Speciation
The development of a new species which cannot reproduce with its previous ancestor.
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Terms: Adaptation
A genetic change within a new species that increases its chances of survival to age of reproduction.
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Mechanisms of Microevolution: Genetic Drift
- Change in the gene pool of a small population due to chance.
- Two examples:
Bottleneck effect.
Founder effect.
- The random fluctuation of allele frequencies in a small population from one generation to the next.
- Eg. frequency of a particular trait could, for no obvious reason, drift from 2% in generation 1, to 11% in generation 2, to 5% in generation 3, etc).
- Effects of genetic drift can be amplified by differences in the number of children raised by couples, or individuals dying prematurely.
- Genetic drift can result in:
Traits being lost from small populations.
Unusual traits, not commonly found in the parent population, & that are often non-adaptive, becoming established.
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Bottleneck Effect
Genetic drift (reduction of alleles in a population) resulting from a random catastrophic event (disaster that drastically reduces population size).
Eg. earthquake, volcano.
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Founder Effect
Genetic drift resulting from the colonisation of a new location by a small number of individuals.
The founding population carry only a small fraction of the original population’s genetic variation. As a result, they may differ both genetically & in appearance, compared with the parent population.
Results in random change of the gene pool.
Eg. Pitcairn Island, in the Pacific, was colonised by the mutineers from HMS bounty in 1790. Today it has a population of ~44 people.
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Consanguinity
Reduced mating opportunities often lead to an increase in in-breeding (consanguinity).
Results in reduced genetic diversity in the population’s gene pool.
In-breeding can result in non-adaptive changes occurring, whereas it can amplify desirably traits but can also greatly increase the risk of unusual, often harmful traits being expressed.
The old Order Amish community of Lancaster County in Pennsylvania, USA is a fundamentalist religious sect who do not marry out or use modern technology.
The Amish community numbers around 18 000 people & shares only eight family names.
There is an above average incidence of inherited illnesses, including a rare form of microcephaly (small brain), albinism, dwarfism, cretinism, webbed fingers & limb girdle muscular dystrophy.
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Mechanisms of Microevolution: Gene Flow
The gain or loss of alleles from a population by the movement of individuals or gametes.
Immigration or emigration.
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Mechanisms of Microevolution: Mutation
Change in an organism’s DNA that creates a new allele that has never been seen before in the organism’s ancestors.
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Mechanisms of Microevolution: Non-Random Mating
The selection of mates other than by chance.
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Mechanisms of Microevolution: Natural Selection
Differential reproduction.
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Genetic Diseases: Sickle Cell Anaemia
Population: Black African populations/India/SE Asia/Italy.
Cause: mutation of the gene responsible for RBC production.
Symptoms: RBCs that have sickle cell shape, reduces oxygen carrying ability on RBC, fatigue, shortness of breath, pain, swelling & inflammation of hands & feet, bacterial infections, sudden pooling of blood in spleen, liver congestion.
Inheritance: recessive trait passed on from affected parents/two carriers.
Effects on Gene Pool: individual homozygous for condition (HBS, HBS) dies early. Individual heterozygous for condition (HBS, HBA), have sickle-cell trait meaning they are resistant to malaria.
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Genetic Diseases: Tay Sach’s
Population: Ashkenazi Jew/Jewish people (from E. Europe)/Cajun
Cause: Missing enzyme essential for fat metabolism.
Symptoms: Build up of fatty substance in the NS. From a few months of age, mental & physical disabilities develop quickly.
Eg. blindness, deaf, unable to swallow.
Inheritance: Recessive trait. Passed on by two carrier parents.
Effects on Gene Pool: Individual homozygous for condition dies early (before reproductive age). Individual heterozygous for condition are resistant to tuberculosis (TB). The more carriers we have, the more chances we have of passing on this resistance.
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Genetic Diseases: Thalassemia
Population: Around Mediterranean Sea/Greek/Italian
Cause: Mutation of the gene responsible for RBC production.
Symptoms: Defects in formation of haemoglobin. Sufferers have few functioning RBCs. Sufferers can have anaemia/iron deficiency/bone malformation/heart defects/enlarged spleen/slow growth rate.
Inheritance: Recessive trait. Passed on by two carrier parents.
Effects on Gene Pool: More mutations in RBC formation, increase severity of the disease. Individual affected with mild thalassemia only have 1-2 mutations. More mutations found in gene pool, greatly increases mortality rate. Resistance for malaria, which increases thalassemia allele frequency in population.
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Speciation
Describes the evolution process that leads to the formation of a new species.
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Speciation: Isolation
Sub-population formed within parent population.
New population established, adjacent to/in isolation from the parent population.
Speciation can occur in several ways.
Isolation of a breeding population: can either occur within the parent population (eg. race or religion) or in isolation from the parent population (eg. migration).
In both cases, interbreeding (gene flow) between the two populations is disrupted.
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Speciation: Adaptation
As a result of natural selection, the sub-population adapts to its new environment.
If the sub-population is small, changes to its gene pool can be amplified by random events such as founder effect (FE) or genetic drift (GD).
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Speciation: Reproductive Isolation
Occurs if the two populations become sufficiently different (structural, behavioural, physiological or genetic) that they can no longer interbreed/produce fertile offspring.
If this occurs, the two populations will be regarded as different species.
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Geographic Isolation
→ Fragmentation of the change:
Changes in climate isolate populations on mountain tops, causing a rise in sea level, creating islands.
Geological changes which raise mountains or create new seaways.
→ Migration:
Migration of a population to a new area.
If the population is small, it may not represent the gene pool of the parent population left behind (FE).
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Ecological Isolation
Populations can become isolated within the range of the parent population.
Differences in food preferences may develop in a part of the population that stop them from freely breeding.
Seasonal isolation may occur.
Eg. different flowering times or breeding seasons.
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Behavioural Isolation
Parts of a population may develop a preference for a particular variety.
They may not mate with any other.
Eg. the snow goose - blue forms tend to mate with blue forms & white forms tend to mate with white forms.
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Mechanical/Anatomical Isolation
Genitalia or floral parts may be incompatible.
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Physiological Isolation
Fertilisation may be prevented by:
Failure of the gametes to be attracted to one another.
The sperm cell receptors of the oocyte may be incompatible with the acrosome.
Pollen tubes cannot find or penetrate sac in flowers.
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Genetic Isolation
Hybrid inviability.
Hybrid offspring die.
Hybrid infertility.
Hybrids survive but are incapable of producing gametes.
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BIogeography
Geographical distribution of species.
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Fossil Record
Fossils & the order in which they appear in layers of sedimentary rock (strongest evidence).
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Comparative Anatomy
Homologous structures, vestigial organs, comparative embryology.
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Molecular BIology
DNA & proteins (amino acids), Haemoglobin, cytochrome C.
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Biogeography
The distribution of living plants & animals suggests that organisms adapted to one environment can invade a new environment & develop specific adaptations to the new conditions.
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Fossil Record
The fossil record provides a record of early life & evolutionary history.
Although the fossil record provides evidence that evolution occurred, the record is incomplete.
As the fossil record becomes more complete, the sequences of evolution become clearer.
We can to some degree use fossils to map evolution.
It is often forgotten when viewing the many dinosaur fossils found in museums that the dinosaurs existed for millions of years & that is why there is a lot of fossils of them.
Most species are lost without ever being fossilised.
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Fossil Definition
Direct or indirect remains of organisms preserved in media such as sedimentary rock, amber, ice or tar.
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Conditions for Fossil Formation
Slow burial - bones may be scattered by predators.
Fast burial - more likely to form complete fossils.
Wet acidic soils - minerals in bones are dissolved, no fossilisation.
Wet acidic soils with no oxygen (peat) - complete preservation of soft tissue & bone.
Alkaline soils - best fossils as bones are not dissolved, can often be petrified.
Volcanic eruptions - heat from volcanic eruptions destroys organic material & fossils are not formed.
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Homologous Structures
Structures in closely related species that are similar in their fundamental layout & construction, although they may serve very different purposes.
This suggests that common ancestry plays a role in the construction of species.
Comparing fossils from ancestors with today’s species can be used to demonstrate how a species have evolved.
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Analogous Structures
Fundamental layout & construction are not similar, although they may serve as the same purposes.
This suggests that there is no common ancestry because there is no reason for the change in structure if the use is the same.
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Vestigial Structures
Many species retain structures that only make sense in light of their ancestry.
These structures are typically reduced & nonfunctional, but they are believed to be inherited from ancestors, in whom they were important to survival or reproduction.
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Comparative Embryology
Closely related species go through similar stages of development, although the adults may not resemble each other very closely.
Some of the many examples:
Limb bud development in whales.
Gill pouches in vertebrate embryos.
Extraembryonic membranes of the amniotic egg.
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Molecular Biology
Proteins: the comparison of the amino acid sequences of similar proteins from different species. The degree of difference between the proteins is used to estimate the degree of difference between the two species.
DNA: a comparison of the base sequences on similar chromosomes of different species. The more similar the base pairs, the more closely related the species.
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Relative Dating
Shows the order in which fossils occurred - does not give exact ages.
Shows which organisms lived together.
Scientists look at where fossils are located within the rock column.
Use the Law of Superposition.
Principles of relative dating allow events to be placed sequentially, which provides interpretation of geologic history & development of a relative timescale.
The principle of superposition: in an undisturbed succession of sedimentary rocks, the oldest are on the bottom & the youngest are on top.
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Law of Superposition
Sedimentary layers are deposited in a time of sequence.
Oldest rock on bottom, youngest at the top.
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Principle of Fossil Succession
Fossils succeed one another throughout time in a regular & predictable order based on the following points:
Life has varied through time.
Fossils are recognisably different form one another.
The relative ages of fossils can be determined.
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Stratigraphy: +/-
Advantages:
Easy to implement.
Cheap to implement.
Disadvantages:
Accuracy relies on index fossils.
Not accurate if earth has been disrupted.
Does not account for earth movement.
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Index Fossils
Characteristics that make effective index fossils include:
Distinctive morphology.
Rapid evolution.
Widespread distribution.
Abundance.
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Index Fossils: +/-
Advantages:
Allows comparison from different sites.
Disadvantages:
Relies on correct identification of index fossils.
Not reliable if site has no index fossils.
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Fluorine Dating
A type of relative dating where two different bone samples are compared to each other.
When bones are buried, fluoride ions from the soil replaces some of the ions in the bone itself.
The older the fossil, the more fluoride it will contain.
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Fluorine Dating: +/-
Advantages:
Accurate for fossils in the same area.
Disadvantages:
Only limited to bones.
Only works with samples in the same are. Cannot compare across sites.
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Absolute Dating
Based upon the fact that atoms of radioactive elements decay to form stable isotopes.
Important data about atoms:
Atoms are the smallest particles of elements.
Atoms are composed of a nucleus containing protons & neutrons, & an outer shell that contains electrons.
The number of protons determines the type of element & is known as the atomic number.
Not all atoms of the same element have the same number of neutrons in their nuclei; these variable forms are called isotopes.
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Radioactive Decay
Some isotopes are unstable/radioactive, & decay to a more stable form. This decay rate is constant & measurable. Geologists measure this rate to determine the absolute ages of rocks.
Decay of the original isotope/parent elements into its product/daughter element is measured in half-lives (hl) - the time it takes for half of the original number of parent atoms to decay into the daughter product atoms.
Absolute dating is accomplished by measuring the ratio of daughter product atoms to parent atoms, & comparing this ratio to the known quantity of a non radioactive element. Measurements are done with a mass spectrometer.
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Radioactive Decay & Absolute Dating
There are three types of radioactive decay & a number of elements that undergo radioactive decay with varying half-lives.
Radioactive elements useful in absolute dating include:
Uranium 235 (Lead 207) hl of 713 mil yrs.
Potassium 40 (Argon 40) hl of 1.25 bn yrs.
Uranium 238 (Lead 206) hl of 4.5 bn yrs.
Rubidium 87 (Strontium 87) hl of 47 bn yrs.
Radioactive dating can only be accomplished on rocks that contain radioactive elements, this usually is limited to igneous rocks that have not been secondarily altered (including volcanic ash).
Determines the specific age of a fossil.
Looks at chemical properties.
Two main types:
Carbon-14 (radiocarbon)
Potassium-Argon
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Carbon-14 Dating
Also known as radiocarbon dating.
Used to date organic substances.
Scientists measure the radiocarbon in the fossil to determine its age.
Measuring the amount of radiation emitted. From this the ratio of C12 to C14 can be estimated.
Half life of C14 is 5730 years (±40).
Can only date specimens up to 60 000 years old.
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Radiocarbon Dating
Can be used on samples containing 300 milligrams to 4 grams final carbon.
AMS - accelerator mass spectrometry. Measures on the atomic level so can measure up to 70 000 years.
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How C-14 Dating Works
Cosmic rays from the sun strike Nitrogen 14 atoms in the atmosphere & cause them to turn into radioactive C14 which combines with oxygen to form radioactive CO2.
Living things are in equilibrium with the atmosphere, & the radioactive CO2 is absorbed and gets used by plants. The radioactive CO2 gets into the food chain & the carbon cycle.
All living things contain a constant ratio of C14 to C12 (1 in 1 trillion).
At death, C14 exchange ceases & any C14 in the tissues of the organism begins to decay to Nitrogen 14 and its not replenished by new C14.
The change in C14 to C12 ratio is the basis for dating.
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C-14 Dating: +/-
Advantages:
Can give a precise date.
Disadvantages:
Can only be used on organic materials.
Cannot date further than 60 000 - 70 000 years.
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Accelerator Mass Spectrometry (AMS)
AMS is a mass spectrometric method for quantifying extremely low concentrations of long-lived radioisotopes such as the commonly used biochemical tracer 14C.
AMS has use when sample is limiting, specific activity is very low, when the level of isotope that can be used is very limited (human studies) & when trying to study events that occur with very low frequency/concentration.
AMS analysis for smaller samples (100 micrograms - 300 milligrams of final carbon).
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Potassium-Argon (K40/AR40) Dating
Scientists determine the age of the rock surrounding the fossil to determine the fossil’s age.
Used only for inorganic substances (rocks & minerals) - usually volcanic rock.
Scientists measure the amount of argon in the rock to determine its age.
Dates rock 100 000 - 200 000 years old & older.
HL of K-Ar is 1.25 bn yrs.
K is an element that goes into many minerals like feldspars & biotite. Ar (a noble gas) does not go into minerals when they first crystallise from a magma because Ar does not bond with any other atom.
When K-bearing mineral crystallises from a magma it wil contain K but not Ar. With passage of time, the K40 decays to Ar40 & is now trapped in the crystal structure where the K40 once was.
Thus, by measuring the amount of K40 & Ar40 now present in the mineral, we can determine how many hl’s have passed since the igneous rock crystallised & thus know the absolute age of the rock.
Ideal for dating early hominid fossils in E. Africa.
They occur in an area that was volcanically active when the fossils were deposited between 1-5 mya.
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K-Ar Dating: +/-
Advantages:
Can give a precise date.
Disadvantages:
Cannot date all types of rocks, only igneous.
Cannot date earlier than 100 000 - 200 000 years.
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Tree Ring Dating
Another form of absolute dating.
As trees grow, they develop concentric rings on the surface of a cut tree trunk.
Each ring represents 1 year of growth & differ in width according to how favourable the growing season was.
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Tree Ring Dating: +/-
Advantages:
Easy to implement.
Cheap to implement.
Disadvantages:
Timber must be preserved well enough so the rings are readable.
Can only date up to 9000 years.
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Primates as Mammals
Fur (body hair)
Homeothermy, the ability to maintain a constant body temperature.
Give birth to live young.
Feed young on milk.
Different teeth types - incisors, canines, pre-molars, molars.
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Characteristics of Primates
Long gestation followed by live birth.
Increased brain size.
Capacity for learning & behavioural flexibility.
Binocular vision.
Diurnal
Colour vision.
Grasping hands.
Finger nails & finger pads with ridges.
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Primate Limbs
A tendency towards erect posture.
Hands & feet possess grasping ability.
Features of hands & feet:
5 digits on each hand & foot.
Opposable thumbs.
Partially opposable great toe.
Tactile pads enriched with sensory nerve fibres at the ends of the ends of digits.
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Primate Maturation
Longer periods of gestation.
Reduced numbers of offspring.
Delayed maturation/long childhood.
High degree of parental care.
Extension of the entire lifespan.
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Primate Habitats
Most live in tropical or semitropical areas of the new & old worlds.
Most are arboreal, living in forest or woodland habitats.
No non-human primate is adapted to a fully terrestrial environment; all spend some time in the trees.
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Primate Diet & Teeth
Generally omnivorous, reflected in their generalised dentition.
Most eat a combination of fruits, leaves & insects.
Most have four types of teeth: incisors, canines, premolars & molars.
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Primate Locomotion
Arm swinging is found among apes.
Prehensile tails, found only among the new world monkeys, are used as an aid to locomotion.
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Classification of Primates
Primate order is divided into two suborders.
Prosimians/lower primates:
Includes lemurs, lorises, tarsiers & tree shrews.
Anthropoids/higher primates
Includes monkeys, apes & humans.
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Prosimians
Most primitive of the primates.
Generally small, between the size of a mouse & cat.
Are arboreal - live in trees.
Have digits with either claws or nails.
Ears can orientate to sound.
Highly developed sense of smell.
Typically omnivorous.
Have large, forward facing eyes that are specialised for night vision (nocturnal).
Shorter gestation & maturation periods.
Dental specialisation called the ‘dental comb’.
Eg: tarsiers, lemurs, lorises.
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Anthropods
Larger brain & body size.
Reduced reliance on the sense of smell.
Greater degree of colour vision.
Bony plate at the back of the eye socket.
Different female anatomy.
Longer gestation & maturation periods.
Fused mandible.
Eg: monkeys, apes, humans.
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Monkeys
Represent about 70% of all primate species.
Divided into two groups separated by geography & evolutionary history:
New world monkeys.
Old world monkeys.
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New World Monkeys
Platyrrhinnes - side facing nostrils with wide septum.
Dental formula - 2:1:3:3.
Almost exclusively arboreal.
Found in southern Mexico, central & South America.
Possess prehensile tails.
Eg: marmosets, tamarins, capuchin monkeys & squirrel monkeys.
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Old World Monkeys
Catarrhines - downward facing nostrils.
Habitats range from tropical forests to semiarid desert to snow-covered areas in Japan & China.
Characteristics:
Most quadrupedal.
Arboreal.
Non-prehensile tail.
Eg: vervet monkey, mandrills, baboons.
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Hominoids
Characteristics distinguishing hominoids from monkeys:
Larger body size.
A sense of a tail.
Shortened trunk.
More complex behaviour.
More complex brain.
Increased period of infant development & dependency.
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Gibbons & Siamangs
Found in the tropical areas of SE Asia.
Adaptations for fast brachiation.
Diet is largely fruit with leaves, flowers & insects.
Basic social unit is a monogamous pair & their offspring.
Males & females delineate their territories with whoops & songs.
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Orangutans (Pogo pygmaeus)
Found in heavily forested areas of Borneo & Sumatra.
Almost completely arboreal.
Males = 90 kg. Females = 45 kg.
Pronounced sexual dimorphism.
Solitary.
Principally fructivorous (fruit-eating).
Adaptations for slow brachiation.
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Gorillas (Gorilla gorilla)
Largest of the living primates.
Confined to forested regions of central Africa.
Males can weigh up to 180 kg, females approx. 90 kg.
Primarily terrestrial, using a posture called ‘knuckle-walking’.
Groups consist of one large silverback male, a few adult females & their subadult offspring.
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Chimpanzees (Pan troglodytes)
Found in equatorial Africa.
Anatomically similar to gorillas particularly in limb proportions & upper-body shape.
Locomotion includes knuckle-walking on ground & brachiation in the trees.
Eat a variety of plant & animal foods.
Large communities of as many as 50 individuals.
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Bonobos (Pan paniscus)
Only found in an area south of the Zaire river.
Population is believed to only number a few thousand individuals.
Exploit the same foods as chimps, including occasional small mammals.
Male-female bonds constitute the societal core.
Sexuality includes frequent copulations throughout the female’s oestrous cycle.
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Primate Evolutionary Trends: Eyes
More towards the front of the face - better 3D (stereoscopic) vision & reduced sense of smell (optical-olfactory shift).
Better colour vision.
Completely enclosed orbit.
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ET: Teeth
Generalised dentition with reduced tooth numbers (I2:C1:PM2/3:M3).
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ET: Limbs
Generalised pentadactyl limbs with improved grasp (opposability of thumbs).
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ET: Hands & Feet
Enhancement of free mobility of the digits, especially of the thumb (opposability) & big toe.
Both used for grasping (prehensile).
Replacement of sharp, compressed claws by flat nails; development of very sensitive tactile pads on the digits.
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ET: Nails
Replace claws.
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ET: Opposability of the Digits
Changes to the relative length of the forefinger & thumb, & modification of the musculature & joints of the hand have improved the opposability of the thumb & the range of grips available to humans.
In contrast, the big toe has largely lost its opposability.
Allows for precision grip & power grip.
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ET: Shoulders
Mobile fore-limbs - shoulder blade on back & well developed collar bone.
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ET: Brain Size
Large brain relative to the size of the body.
Progressive shortening of the snout & reduction in the sense of smell.
Progressive expansion & elaboration of the brain, especially of the cerebral cortex.
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ET: Pregnancies
Single pregnancies.
Extended period of dependency on parents.
Body tends to get larger.
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ET: Extended Gestation & Maturation
Primates are born at earlier stages of development than many other animals.
Prolongation of postnatal life periods.
Humans are born at a particularly early stage because of their larger brain. If born later, the baby’s head would be too large for the mother’s pelvis.
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Who Were the Hominins?
A group of hominoids (apes & humans) who habitually stood upright & moved bipedally.
Includes modern humans & their ancestors since they diverged from the ape lineage.
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Advantages of Bipedalism
→ Improved food acquisition.
Patchy grassland environments.
Enables walking longer distances for foraging trips.
Invention & use of food gathering tools.
Byproduct of reduced forelimb usage for locomotion.
→ Improved predator avoidance.
Enhances height.
Increased field of view to see over tall grass in grassland.
Still maintain tree-climbing ability.
→ Improved reproductive success.
Home base & strong family bonds.
Male gathered food & carried it to home base.
Reduced need for female to be mobile.
— Advantages:
More constant social relationships.
Reduced infant injury.
More care for offspring, more offspring.
An adaptation to terrestrial living.
Bipedalism is not necessarily faster but more sustainable over long distances.
Protection from predators.
Bipedalism did free the hands for tool-using but what tools? Possibly for food transport.
Reduced exposure to the sun.
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Bipedalism: Basic Principles
In order to stand upright, our centre of balance has to fall within the area described by our feet.
Standing with a lowered centre of gravity & increased base area by spread feet, stance can become more stable.
In order to become more efficient upright walkers, adaptations were needed to:
Bring the weight of the body above the feet.
Support the weight of the upper body.
Improve the efficiency of the striding gait.
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Upright Bipedalism - Head
In humans, an inward curve has developed in the lumbar region of the spine & the pelvis has been tilted into an upright position.
The lumbar vertebrae becomes robust & the pelvis becomes short & bowl-shaped. Both structures are load-bearing, carrying the weight of the upper body.
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Upright Bipedalism - Femur/Leg
The roles of the gluteus maximus & gluteus medius are modified. The gluteus maximus becomes extensor (ie. pulls the thigh backwards) & the gluteus medius stabilises the pelvis when we bear the weight of the body on one foot.
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Hominoids
All apes - gibbons, gorillas, chimps, orangutans, humans.
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Hominids
All modern & extinct great apes. Gorillas, chimps, organutans, humans & their immediate ancestors (NOT gibbons).
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Hominin
Any species of early human that is more closely related to humans than chimpanzees, including modern humans themselves (at this point, this includes the genuses homo, australopithecus, ardipithecus, paranthropus).
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Australopithecus afarensis
Widely regarded as the ancestor of later australopithecine & hominin species.
Lived in E. Africa ~3.9 - 2.8 mya.
Displayed a mix of ape & human features.
“Lucy” was discovered in Ethiopia.
Said to be an adult female of about 25 years.
She was about 107 cm tall (small for her species) & about 28 kg in weight.
Ape-like features:
Small brain case - averaging 430 cc.
Prognathic (jutting-out) face.
U-shaped palate vs, the parabolic shape of modern humans.
Reduced canines.
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Australopithecus afarensis: Hominin Footprints
Fossilised hominin footprints in Laetoli, Africa.
The footprints were formed 3.5 mya when at least two individuals walked over wet volcanic ash.
The wet ash hardened like cement & was then covered by more ash.
The The footprints demonstrated that hominins were bipedal walkers at least 3.5 mya.
Many scientists propose the footprints were made by A. Afarensis, whose fossils are found nearby.
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Australopithecus africanus
South Africa (Transvaal region) was the home to the species which lived ~ 3.2 - 2 mya.
Many features of the cranium are ore evolved than that of earlier A. afarensis.
A more globular cranium & slightly higher ratio of brain size to body size.
Reduced teeth size & prognathism.
May represent two species or one very sexually dimorphic species.
Females grew to about 110 cm, males to around 135 cm.
Ape-like features.
Cone-shaped rib cage.
Long arms.
Cranial capacity was approx. 480 cc.
Narrow birth canal.
Not specialised to striding gait.
Physical features.
Smaller brow ridge.
Slightly arched forehead.
Central foramen magnum.
Diastema rarely seen.
Canine & incisors similar length.
Many features of the cranium are more evolved than the earlier A. afarensis.
A more globular cranium & slightly higher ratio of brain size to body size.
Reduced teeth size & population.
Less interest in A. africanus since it was removed from a position of ancestry to humans.
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What happened to Australopithecines?
Two hypothesis on the extinction of Australopithecines:
A change in the limit or decrease in their food availability due to the climate drying & decreasing in temperature.
Could not compete with homo, due to finding Australopithecine bones in their hearth.
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Paranthropus robustus
South Africa, 2.3 - 1 mya.
Short, broad face with deep zygomatic arches & large temporal fossa. Large individuals (males?) have sagittal crests.
Very large cheek teeth covered with thick enamel.
Wear patterns on teeth indicate herbivorous diet of harder, more resistant & perhaps smaller food items than A. africanus.
Lived in secondary grasslands near rivers & wetlands.
Physical features:
Central foramen magnum.
Brain approx. 520 cc.
Larger individuals (males?) have sagittal crests.
Very molars covered with thick enamel.
Jaws were large & robust.
Face more prognostic than other species.
Pelvis broad but not built for striding gait.
Arms were long compared to legs.
Cone shaped rib-cage.
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Homo habilis
Lived in E. Africa (Tanzania) 2.3 - 1.5 mya.
Made stone tools.
Also called ‘handy man’.
Short with disproportionately long arms compared to modern humans (= continued arboreal activities?).
Physical features:
Bigger brain - avg. 610 cc.
Brain case more rounded.
Skulls suggest portions of the brain associated with speech were enlarged.
Hypothesised ability to speak may have led to cooperative hunting of meat & the advent of material & social culture.
No sagittal crest.
Less prognostic face with more pronounced lower jaw.
No canine diastemas.
Smaller zygomatic arch.
Associated with Oldowan stone tools - simple tools flaked on one edge.
Females about 110cm, males around 135 cm.
Reduced prognathism.
Central foramen magnum.
More rounded dental arcade.
Legs short compared to arms.
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Homo erectus
Migrated out of Africa into Asia & Europe, and survived until about 100 000 years ago.
Was probably the ancestor of H. sapiens.
Acheulean tool industry - stone hand axes & knives.
Shorter & stocker than modern humans.
Physical features:
1050 cc average brain size.
Long sloping forehead.
Large brow ridge.
Skull long & broad with midline keel.
Jaw large & thick.
Molars smaller in size.
Limbs similar to modern humans, but bones were thicker.
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Why was H. erectus more Successful?
Less sexual dimorphism = probable pair bonds (marriage?).
Less hair on the body = wearing of furs, other clothing.
Wearing furs = ability to live further north.
Culture (fire, tools, hunting, campsites, simple art, clothing).
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Homo neanderthalensis
Were ‘cousins’ of modern humans - they evolved in southern Europe during the ice age.
Had large brains & were stocky & strong.
Became extinct about 28 000 years ago but might have contributed to the gene pool of modern Europeans.
Physical features:
Females about 156 cm, males about 168 cm.
Robust skeletons.
Increased brain size - avg. 1500 cc.
Brain case long.
Development of occipital bun.
Pronounced brow ridge.
Decrease in robustness of front teeth indicating use of tools.
Bony chin absent.
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Neandertal Culture
Homeosites: in caves, also in the open (near rivers, framed with wood, covered with skins).
Burial: buried dead with spices & bedding
Language: debatable as to whether they could talk.
Tools: mousterian tradition - flaked tools with wood handles.
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What Happened to the Neanderthals?
Homo neanderthalensis coexisted with Homo sapeins for at least 20 000 years, perhaps as long as 60 000 years.
What happened to them?
Interbred with Homo sapeins?
Killed off by Homo sapeins?
Homo sapeins drove Neanderthals into extinction by competition?
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Homo sapiens (archaeic)
Evolved in Africa about 300 000 years ago.
Migrated out of Africa & either interbred with or displaced the populations of H. erectus & H. neanderthanlensis they came into contact with.
Oldest fossils are designated archaeic H. sapeins.
Made advanced stone tools.
Accomplished hunters.
Hunted cooperatively.
First to have complex language?
Hominins with larger brains & more modern cranial features than classic H. erectus.
Taxonomy is problematic: some fossils could be H. erectus. Others could be direct ancestors of later Neanderthals or archaic forms of H. sapiens sapiens.
1600 cc cranial capacity.
With the appearance of Cro-Magnons, humans human evolution became almost entirely cultural rather than biological.
Physical features:
Short slender trunk with long limbs.
Average cranial capacity of 1500 cc.
Back of the skull is rounded.
Limited brow ridge. Tall forehead.
Parabolic dental arcade.
Legs long when compared to arms.
Pelvis bowl shaped.
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Homo sapeins - modern
Cranium/brain averages 1300 cm3.
Cranium smooth & domed.
Steep forehead with greatly reduced brow ridge.
Temporal filling eliminates wasting in temporal area.
Flat facial profile - little prognathism of the upper jaw.
Small molar & pre-molar teeth.
Chin.
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Hominin Evolution
Development of upright bipedalism.
Appearance of more less specialised dentition.
Expansion of the brain.
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Hominin Evolutionary Trends: Skull
Brain/cranium became larger.
Cranium becomes smoother & more domed.
Foramen magnum moves towards centre of cranium.
Sagittal crest not present.
Unchallenged area for attachment of neck muscles becomes smaller.
Brow ridge becomes smaller.
Temporal filling eliminates waistline in temporal area.
Facial profile becomes flatter - less prognathism of the upper jaw.
Michael area for attachment of neck muscles becomes smaller.
Crow ridge becomes smaller.
Temporal filling eliminates waiting in temporal area.
Facial profile becomes flatter - less prognathism of the upper jaw.
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Hominin Evolutionary Trends: Jaws & Dentition
Dental arcade becomes more parabolic.
All teeth become similar in size.
Specialised to more generalised teeth.
3 cuspids - 4 cuspids - 5 cuspids.
No diastema.
Lower jaw & teeth become smaller.
Chin develops in modern humans.
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Hominin Evolutionary Trends: Hands & Feet
During the course of hominin evolution, the arms have become shorter & the manipulative ability of the hands has improved.
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Climate Change & Evolution
Climate change in Africa around 3 mya.
Main driving force in the evolution of the hominins.
Onset of cooler, drier & more valuable conditions led to a reduction in tropical rainforest & the appearance of open woodland & savanna grasslands.
Changes to climate & vegetation coincided with changes in the fauna, including the appearance of new species of large plant-eating mammals (good potential food source).
It was also when the first hominins appeared.
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Tool Cultures
Oldowan:
- Simple stone tools.
- Homo habilis
Acheulean:
- Roughly made hand axes.
- Homo erectus
Moisterian
- Finely made hand-axes, blades & points.
- Homo neaderhtalensis
Aurignacian
- Made from bone & stone.
- Shaped like a blade, not like flint.
Solutrean:
- Advanced flint tool.
- Also made ornamental beads & bone pins as well as prehistoric art.
Magdalenian:
- Made of bone & antler.
- Used for a range of purposes such as fine needles to barbed spear points.
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Fire
The ability to create fire provided early humans with warmth & protection against wild animals.
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From Hunter-Gatherer to Farmer
The transition from hunting & gathering to farming provided humans with a reliable source of food. This enabled them to settle down & build permanent towns & villages.
This stage of human development is known as the Neolithic revolution.
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Clothing
Enabled early humans to survive the ice age & to colonise the earth’s most severe climates.
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Language & Writing
Enabled humans to communicate with one another & to record & pass on their ideas.
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Human Evolution & Technology
The development of technology has largely quarantined humans from the forces that drive natural selection.
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Medicine
Has improved health & extended human life span.
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Industrial Revolution
New technologies led to industrialisation & the growth of huge cities.
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Consequences
As well as improving the living standards of some people, human activity has also resulted in over population, pollution & the depletion of precious resources.
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Noses
Nose shapes are adaptations to warm or cold environments.
(Increase or decrease SA:Vol)
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Human Body Types/Variation
Humans adapted to cold climates are often lateral in build; those adapted to warm climates tend to have a linear build.
Normal human height ranges from 1-2.5m.
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Sickle Cell Anaemia Trait
- Both haemoglobin S & A are produced.
- More haemoglobin A is produced than S.
- RBCs are supple & do not block capillaries.
- These RBCs make the body more tolerant to Plasmodium sp. infection, reducing death from malaria.
