Evolution & Genetics

Question 1

Theory of evolution

Answer 1

• Charles Darwin & Alfred Russel Wallace
• The central idea of biological evolution is that all life on Earth shares a common ancestor. It does not mean we have evolved from apes, but more that humans and great apes share a common ancestor.
• Organisms are (successful) adaptations of previous generations – Natural Selection

Question 2

Requirements for the evolution of populations

Answer 2

1. Principle of inheritance
   
   • Physicial or behavioural traits that we can provide to the next generation → heritability
2. Principle of variation
   
   • Individuals within a species show variation in their traits e.g. hair colour, chronotype/diurnal preference
3. Principle of adaptation
   
   • Some versions of traits are more adaptive than others e.g. lack of blondes around the equator as being brunette has an advantage because it protects your head from sunburn
4. Principle of evolution
   
   • As a consequence of being better adapted to an environment, some individuals will survive and produce more offspring, who will inherit the same advantages. This is called ‘fitness’ (natural selection).

Question 3

Adaptation to the environment

Answer 3

• Stabilising selection: the individuals with the middle expression of a variation are favourite in terms of adaptation to the environment - stabilisation of the population
• Directional selection: one end of the distribution is particularly well adapted. e.g. polar fox evolve because they were adapted to white snowy environment
• Diversifying selection: the population is split in two different populations which will eventually lead to new species → the current theory of human evolution states that humans have evolved from the diversifying selection of a common ancestor whereby geographical changes in Africa led to the differentiation of environments between West Africa (rainforest environment) and East Africa (savannah, dry environment). Apes continued as normal in West Africa whilst in East Africa, upright walking position was beneficial to the dry environment.

Question 4

Natural selection & reproduction

Answer 4

1. Individual selection
   
   • Animals behave to maximize the number of copies of their genes left in the next generation by reproduction → Individual self-reproduction
   • E.g. male peacock has bright blue wings for sexual selection, to attract females
2. Kin selection
   
   • Reduce the reproductive success of an individual to increase the success of a relative because you share more common genes
   • e.g. in a beehive, the queen bee is in charge of reproducing the genes of the entire population so all the other bees help the queen to reproduce herself
3. Reciprocal altruism
   
   • An organism acts in a manner that temporarily reduces its fitness while increasing another organism’s fitness, with the expectation that the other organism will act in a similar manner at a later time → synergistic behaviours
   • E.g. monkeys grooming each other with the expectations that other monkeys will return the favour

Question 5

Evidence in support of the theory of evolution

Answer 5

• Biogeography: Distribution of organisms on Earth; evolution of unique species on islands e.g. koalas in Australia
  
  • Evolution has been observed in progress. For example an 18-month drought on one of the Galapagos Islands left only large, difficult to eat seeds and increased the beak size in one species of finch (=bird).
• Fossils: selection in various forms in progress e.g. reptiles and bird fossiles have shown they have evolved from a common ancestor, fossils in West and East Africa have provided evidence for evolution from a common ancestor with the great apes
• Structural similarity: two types of structure
  
  • Homologous structures are those organs whose underlying similarity arises from their being derived from a common ancestral structure. For example, the wing of a bird and the forelimb of a human are homologous.
  • Analogous structures are those whose similarity comes from their performing a similar function, rather than their arising from a common ancestor. Therefore, for example, the wing of a butterfly and the wing of a bird are analogous. → evolution’s way to solve the same problem in different ways - diverisfying selection
• Embryology: embyos of different species roughly at the same developmental stage, we can see they all have similar organs e.g. even human embryos have tails
• Molecular biology: At the most basic level, all living organisms share: a genetic code, genetic material - DNA; basic process of gene expression (transcription and translation); the same molecular building blocks, such as amino acids → homologous structure serving different functions with the same build-up
• Human genome project: If evolution is true then we might also expect that closely related organisms will be more similar to one another than more distantly related organisms → evidence of common ancestor

Question 6

Characteristics of human evolution

Answer 6

• Evolution is a slow process
• Evolution has no ‘aim’ nor is any part of it a pinnacle.
• Not all existing behaviours or structures are adaptive
  
  • Spandrels—phenotypic characteristic that is a byproduct of the evolution of some other characteristic, rather than a direct product of adaptive selection (e.g., human chin, redness of blood have no adaptive purpose)
  • outdated adaptations to previous environments (e.g., humans used to be endurance running but no longer need to be, which explains why we still have the ability to do so →ironman competitors. Bramble & Liebermann, 2004 found an African tribe that still uses endurance running as their main method of hunting)
• Evolution is gradual vs punctuated equilibrium (=what we see and observe, not to be confused with pinnacle)
• Social Psychology: ‘maladaptive’ behaviours (e.g. psychopathy, aggression, jealousy, rape)
  
  • Evolutionary Psychology : potential adaptive benefits? e.g. obesity can be explained by ancestors having a beneficial survival advantage if they had the capacity to eat more when food was available, as food was not always available as it is now

Question 7

Evolution of the brain

Answer 7

• Roth & Dicke, 2005:
  
  • Homo brain is proportionally much bigger to other species, relative to its body weight
  • Homo neanderthalensis is the only species with a bigger brain:body weight ratio than homo sapiens

Question 8

Behaviourism

Answer 8

• Skinner & Watson, 1950s
• All behaviour is the product of learning (nurture)

Question 9

Ethology

Answer 9

• The study of animal behavior in the wild instinctive (nature) behaviours
• Originated in Germany in the 1950s

Question 10

Nature vs nurture debate

Answer 10

• Many factors other than genetics (nature) or learning (nurture) have an impact on behaviour
• “Nurture” now encompasses learning and environment
• Generally accepted that behavior is a product of nature and nurture
• Ill-posed question: how much is determined by each
• Genetic and experiential factors do not merely combine in an additive fashion → interactionism

Question 11

Genes and evolution

Answer 11

Question 12

DNA molecules

Answer 12

• Forms the genotype of an organism
• Information bank found within the nucleus of every cell
• Every time an organism grows a new cell a new copy of the DNA is created
• It is important that every copy of the DNA is identical, since any errors copying the genotype may prevent the cell from functioning properly.
• In 1953, Watson and Crick figured out that DNA had a double-helix structure and showed how it copies itself with such amazing accuracy.
• When DNA replicates, the helix unwinds and each strand produces an exact mirror image copy of itself. This ensures that each copy is identical to the original.
• DNA segments = genes
• Segments are organised in different base pairs
• 3 segments code for a gene
• DNA exists in form of chromosomes
• DNA is copied/replicated from one generation to the next (almost) errorless
  
  • In evolution, the emphasis is on almost

Question 13

Chromosome

Answer 13

Thread-like strand of DNA that contains the genetic code

Question 14

Genotype

Answer 14

The genetic constitution of an individual organism

Question 15

Human chromosomes

Answer 15

• 23 chromosome pairs
  
  • ​22 identical pairs
  • 1 different pair: sex chromosomes
    
    • Female: homogametic sex (XX)
    • Male: heterogametic (XY)
• Each chromosome carries genes
• Each inherited factor is a (combination of) gene(s)
• Genes occur in pairs
• Genes that control the same trait are called alleles
• Homozygous – 2 identical alleles
• Heterozygous – 2 different alleles
• dominant alleles/traits and recessive alleles/traits

Question 16

Mutations

Answer 16

• Copying errors in DNA replication
• Most of these mutations are deadly. Consequently organisms have special enzymes whose job it is to repair faulty DNA.
• Mutations may be caused by a number of factors including radiation, viruses, or carcinogens (cancer-causing materials).
• Some mutations are adaptive
• Examples:
  
  • Phenylketonuria (PKU) - leads to difficulties in processing Phe (a nutrient present in most foods)
  • Sickle cell disease - tiny mutation that leads to blood cells getting limited oxygen. Note this mutation is advantageous (=adaptive) in Africa as it immunises populations from malaria

Question 17

Selective breeding of “maze-bright” and “maze-dull” rats study

Answer 17

• Cooper & Zubek, 1958
• Two groups of rats that were separated based on their performance in a standardized maze problem.
• Those that performed best were bred with each other, as were those that performed most poorly.
• Over relatively few generations, there was a complete separation in performance, with none of the maze-bright rats overlapping in scores with maze-dull rats.
• However, the selective breeding appeared to be specific to the maze tests that were used and did not affect learning ability more generally; moreover, maze-dull rats reared in an enriched environment could perform as well as maze-bright rats.
• Highlights the importance of the interaction between the environment and the genes

Question 18

Minnesota twin study

Answer 18

• Shields, 1962
• Study of monozygotic MZ (identical i.e. exact same DNA) and dizygotic DZ twins (not identical - different DNA)
• Minnesota study of twins reared apart showed that identical twins are more similar to each other than fraternal twins on all psychological dimensions
• Correlations of the IQ’s of identical twins whether raised together or apart is larger than that of
  fraternal twins raised together
• Critique:
  
  • Multiplier effect – genetically similar individuals seek out similar environments. Twins when reared apart will typically be given to parents from upper-middle class, so similar environments. → environment effect is underestimated
  • Turkheimer et al. (2003) showed that the heritability of IQ was near 0 in impoverished twins and near 1 (maximum) in affuent twins ⇒ effect cannot be generalised to populations from dissimilar environments

Question 19

Polderman et al., 2015

Answer 19

• The largest meta-study of twins in history—which examined 14.5 million sets of twins
• “If we pool all data, the balance between nature and nurture is near perfect: across all traits the heritability is 49 percent, and environmental influences account for 51 percent,”
• “When visiting the nature versus nurture debate, there is overwhelming evidence that both genetic and environmental factors can influence traits and diseases”

⇒ It is not nature vs nurture - it is nature and nurture

Question 20

Epigenetics

Answer 20

• The science of how the environment influences genetic expression
• What counts is not what genes you have so much as what your genes are doing.
• And what your genes are doing is influenced by the ever-changing environment they’re in.
• The lifestyle you have determines which genes are turned on/off ⇒ methylation
  
  • Most genes we have are switched off and those are the genes we share with chimpanzees (with which we share 98% of our genetic code) i.e. the genes are there but they are not expressed due to the difference in lifestyle we have with chimpanzees
  • This is not set in stone: subsequent generations can activate these genes by changing their environment → reversible process

Question 21

Methylation

Answer 21

DNA methylation is a process by which methyl groups are added to the DNA molecule. Methylation can change the activity of a DNA segment without changing the sequence. When located in a gene promoter, DNA methylation typically acts to repress gene transcription i.e. silence the gene, switch it off.

Question 22

Michael Meaney studies

Answer 22

• What makes a good rat mama? ⇒ love = licking
• When babies grew up, they carried their mama’s behaviour with them and passed it on to the next generations
• Could it be that this particular group was genetically predisposed to produce caring mothers?
• Researchers swapped babies from low licking mothers to high licking mothers and vice versa and found that when the mother was a high licker, the baby becomes a high licker too regardless of whether they are genetically related or not
• Does that mean that genes have nothing to do? DNA analysis showed that the methyl groups (which silence a gene = switching it off) in rats from low licking mothers were still attached whereas in the rats from high licking mothers, these methyl groups had disappeared.
• This was also true for rats that had been adopted by high licking rat mothers

⇒ the care these rats received from their adopted mothers actually physically altered their genetic expression