Midterm 1 important Flashcards
(138 cards)
1
Q
When did homo sapiens migrate out of Africa
A
about 100,000 years ago
2
Q
bipedal walking results in constraints in
A
size of pelvic inlet/outlet in females which can make some newborn deliveries difficult
3
Q
change in shape & position of the larynx necessary for human speech
A
has resulted in ^ likelihood of sleep apnea
4
Q
post-reproductive period when a direct fitness advantage is not possible
A
therefore, primary investment in maintenance and repair is prior to peak reproductive age and declines in post reproductive years
5
Q
tradeoff of going into puberty early
A
- mismatch b/w biological and psychosocial maturation
- individuals have a higher likelihood of risk-taking behavior, depression, and even suicide
6
Q
Antagonistic pleiotropy
A
traits that have been selected to have benefits in early life but then have detrimental effects later in life
7
Q
exps of antagonistic pleiotropy
A
- stem cells in tissues (promote tissue maintenance and repair, but later can cause neoplasia [cancer])
- IGF-1 (promotes fetal, muscle, and skeletal growth in early years, but can lead to cancer later on in life)
- testosterone can promote health in young males, but later lead to prostate cancer & heart disease
8
Q
sexual selection
A
- differential reproduction as a result of variation in the ability to obtain mates
- variation in the number of offspring produced as a consequence of a competition for mates
9
Q
why are humans typically monogamous
A
relatively small degree of sexual dimorphism in body size in humans
10
Q
what enables alleles that cause monogenic disease to NOT be eliminated from the population
A
- Heterozygote advantage
- Effects aren’t apparent until after peak of reproductive age
- recurrent mutation
11
Q
Heterozygote advantage
A
- deleterious effects of an allele are confined to or are expressed in the homozygotes state, but the heterozygote for the allele have some short of selective advantage
- sick cell, cystic fibrosis, tay-sachs, phenyketonuria
12
Q
Effects aren’t apparent until after peak of reproductive age
A
- the effects of the deleterious allele mau not become apparent until after oeak reproductive ages, so the parent may pass on the allele to a child before negative selection has had a chance to operate
- huntington’s chorea/disease
13
Q
spontaneous mutation
A
- mutation
- hemophilia, aneuploid, trisomy
- only in the homozygous X chromosomes, since males only have one X chromosome all males with the allele have hemophilia, also explains why its rare in females
14
Q
examples of diseases of autoimmunity, (defense are inappropriately and excessively activated causing person’s antibodies to attack their own tissues)
A
eczema, rheumatoid arthritis, and inflammatory bowel disease
15
Q
Linnaeus
A
- hierarchical classification of organism
- bionomial system of species names
- thought species were fixed and immutable
16
Q
Jean-Baptiste Lamarck
A
-proposed concept of evolution
17
Q
Darwin & Wallace
A
- natural selection and evolution
- Darwin “On the Origin of Species”
18
Q
Mendel
A
- inheritance of peas
- genetics
- understanding of genetics aid development of evolutionary science
19
Q
Ronald A Fisher & Julian Huxley
A
- Modern synthesis
- fusion (merger) of Mendelian genetics with Darwinian evolution that resulted in a unified theory of evolution.
20
Q
Watson and Crick
A
double helix of DNA
21
Q
microevolution
A
refers to slight relatively short term changes within a species
22
Q
macroevolution
A
usually meaning the evolution of substantial phenotype changes, typically great enough to place the changed lineage into a distinct new species or higher taxon
23
Q
trait
A
distinct variant of phenotypic character of an organism that may be inherited, environmentally determined or be a combination of the both
24
Q
fitness
A
=reproductive success
- selection operates to enhance fitness
- enhancement of fitness, does not necessarily operate to enhance health or longevity
25
Ultimate causes
- the evolutionary explanation for why a person gets sick under certain circumstances
- WHY question
26
Proximate causes
the anatomical, physiological molecular, and pathophysilogical mechanisms that lead to a biological phenomenon
27
relevant histories
- 1 medical history
- 2 development history
- 3 evolutionary history
28
Non-human primates
-often arboreal species, live in tropics
-Large brain compared to body size, especially in greater primates
-Opposable thumbs on hands and feet.
-Typically one young per pregnancy.
-Flattened face compared to non-primate mammals.
-Specific pattern of dentition.
-Eat primarily plant foods and also some
invertebrates.
29
Adaptive radiation
• Adaptive radiation is an evolutionary phenomenon where there is a rapid appearance of multiple related species from a common precursor species, each adapting to a different ecological niche.
-thought to occur when a species enters a new ecosystem
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Adaptive radiation exapmle
- Darwin's finches
- attempted to minimize competition
- variation in beak size and shape
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primate evo
* The first primates appeared around 65 million years ago
* Primate evolution is characterized by a series of adaptive radiations leading to the prosimians (lorises, tarsiers, & lemurs), Old World monkeys, New World monkeys, lesser apes, great apes, and hominins.
* Approximately 200 extant primate species are in the world today.
32
Lesser Primates (Prosimians)
```
• Lorisiformes in Africa & Asia
-bushbabies/galagos
• Lemuriformes in Madagascar
-lemurs, indris, sifakas, aye-aye
• Tarsiiformes in SE Asia
-tarsiers
• A type of primate that includes bushbabies, lorises, tarsiers, and lemurs but not monkeys, apes, or humans
```
33
Greater Primates
* New World Monkeys
* Old World Monkeys
* Lesser Apes (gibbon, siamang)
* Greater Apes (orangutan, gorilla, chimpanzee, bonobo)
* Humans
34
Old world monkeys:
| Sub-family Colobinae
colobus monkeys, proboscis monkeys, leaf monkeys, snub-nosed monkeys, pig-tailed monkeys, languars.
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Sub-family
| Cercopithecinae
macaques (e.g., rhesus monkey), baboons, geladas, mandrills, swamp monkeys, patas monkeys, talapoin monkeys, guenons, mangabeys.
36
Earliest world monkeys arrived to the New World from the Old World when?
at least 36 million years ago
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New World Monkeys
| Cebidae
```
marmosets
tamarins
Goeldi’s monkeys
squirrel monkeys
capuchin monkeys
```
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New World Monkeys
| Atelidae
```
spider monkeys
howler monkeys
owl monkeys
titi monkeys
wholly monkeys
uakaris
sakis.
```
39
Hominoids, hominin, & hominid
- Hominoids: Hominoidae superfamily of apes and humans (gibbon, siamang, orangutan, gorilla, chimpanzee, bonobo, hominin/hominid)
- Hominid in anatomical classification
- Hominin in genetic classification and each = human lineage: restricted to humans and their extinct ancestors after the division from chimpanzees and bonobos.
40
Anatomical Classification
Superfamily Hominoidea extant apes & humans
MUST LEARN
- hylobatid family: Lesser Apes
- gibbon & siamang
- Pongid family: Great Apes
- Pongo spp. (orangutans) [SE Asia]
- Gorilla spp. (gorillas)
- Pan spp. (chimpanzees & bonobos)
- Hominid family
- Homo spp. including homo sapiens
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Molecular evidence shows the following times for when different lineages split off from the hominoid lineage
MUST KNOW
* Chimpanzee & bonobo lineage: at least 7-8 million years ago.
* Gorilla lineage: 9-10 million years ago.
* Orangutan lineage: 12-15 million years ago.
* The last common ancestor for the human lineage and great apes was about 15 million years ago.
* Genetic studies estimate that the hominin-chimpanzee split is at least 7-8 million years ago
42
Lesser Ape: Gibbon & Siamang gibbon
* South East Asia
* Symphalangus syndactylus
* Primarily eat leaves and fruit
* Arboreal & tail-less
* Minimal sexual dimorphism
* Live in 25-30 years in wild & to 40 years in captivity
* Socially monogamous families with mating pair and may have as many as 10 offspring in reproductive years
* Adult female is the dominant animal in the group
* Siamangs are physically independent by age 2 years and sexually mature at age 7 years
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Sexual Monogamy
the practice of having a sexual relationship with only one partner during a period of time
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Social Monogamy
- the practice of living with only one partner during a period of time, however, members of this socially monogamous partnership may have sex with other individuals and may even conceive a child with these other partners
- exp: birds
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Polyandry
one female paired with more than one male
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Polygyny
one male paired with more than one female (e.g. in gorillas)
47
Promiscuity
having multiple partners and frequently switching partners (e.g. in bonobos)
48
Orangutans (Pongo) rainforests of Borneo and Sumatra
-Live in rainforests of Borneo and Sumatra.
• Spend a lot of time in the canopy of the forest.
• Largest living arboreal species.
• Primarily herbivorous eating leaves, shoots,
and fruits with 65-90% of diet as fruit.
• Mature adult males are solitary much of time.
• Two species.
• Pongo pygmaeus: Bornean orangutan.
• Pongo abelii: Sumatran orangutan.
49
Female Orangutan sexual maturity
* Females become sexually mature at about 8-9 years of age
* Age of female adult maturity is 12 years.
* Typically do not have their first baby until 14-15 years of age.
* Gestation about 8.5 months.
* Infant newborn weight 1.5-2.0 kg (3.3-4.5 pounds)
50
Orangutan mating system
* Resident females live with their offspring in defined home ranges that overlap with those of other adult females, which may be their immediate relatives
* One to several resident female home ranges are encompassed within the home range of a resident male, who is their main mating partner
* Sexually polygynous mating system with one male with multiple females, however this is NOT a socially polygynous system
51
Male orangutan sexual maturity
• Male orangutans have a particularly interesting bimodal physical development, referred to as bimaturism or arrested development, which is influenced by the social context in which they live.
• Subadult, or unflanged, males (ages 8 to 15 years) achieve sexual maturity with fully descended testicles and are capable of reproducing but remain in a morphological state quite similar to adult females.
• Between 15 and 20 years old, when the proper social conditions arise, they develop secondary sexual characteristics with characteristic long-calls of a socially mature adult males (also called flanged males).
• When the proper social conditions arise, mainly in the absence of a resident male, they begin to develop the characteristic cheek pads, throat pouch, long fur, and behaviors of resident adult males.
-Flanged Male Borneo orangutan, Pongo pygmeus
52
Gorilla Females
* Females in the wild become sexually mature at around 8 years of age but usually do not have their first baby until 10 years of age.
* Gestation is 8.3-9 months.
* Weight of newborn infant is 1.8-2.3 kg (4-5 pounds).
* Sexual and social polygynous mating system with one male with multiple females
53
Gorilla Male
* Males in the wild become sexually mature at around 11 years but often do not start breeding until they are around 15 years of age.
* Males will slowly begin to leave their original troop when they are about 11 years old, traveling alone or with a group of other males for 2–5 years before being able to attract females to form a new group and start breeding.
* Adult males who are over 12 years of age are referred to as silverbacks and can lead a troop of 5-30 gorillas of various ages and sizes.
* Baby gorillas will breast feed for around 4 years and post-weaning the adult males contribute to the care of the children, however mothers are still the primary caretakers.
54
Common chimpanzee
-Pan troglodytes (KNOW THIS) WEST & Central Africa
• Up to 1.7 m (5’6”) in height when standing upright.
• Weight males 40-54 kg (90-120 pounds).
• Weight females 32-45 kg (70-100 pounds).
• Brain size 400cm3
• Terrestrial & climb trees
• Walk on all fours using knuckles for support.
• Total testicle size of chimpanzee is large at 4
ounces compared to 1 ounce for gorilla and 1.5 ounces for Homo sapiens.
• Live in West and Central Africa.
55
Mate choice and ratio of
| testes/body size
• Relatively small testes as in humans is associated with relatively monogamous mating systems.
• Large testes like in chimpanzees are associated with promiscuous mating systems where both females and males have multiple partners (Fig 7.2); because there are multiple male partners, releasing more sperm per ejaculation enhances sperm competition for egg.
-Testes are larger in males in species where there is a multi-male mating system and sperm competition would be predicted to be a factor in fitness
56
Bonobo, Pan paniscus
• Bonobos are endangered and are found in the wild only in the Democratic Republic of Congo.
• The common chimpanzee and the bonobo are the closest extant relatives to humans.
• Bonobos are likely matriarchal and have a promiscuous mating system with engagement in frequent casual sexual activity, both heterosexual an homosexual.
• Make love face to face; only species other than Homo sapiens that copulate in this position.
-Central Africa
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Bonobo vs. Chimpanzee
* A bit shorter and thinner than the common chimpanzee with a height of 70-90 cm (2.3’- 3’) and weighing form 55 - 110 pounds (25-50 kg) in the wild.
* Brain size is 300-400 cm3 while brain size of common chimpanzee is 400 cm3.
* Comparatively longer limbs than common chimpanzee.
* Walk upright more than common chimpanzee.
* Mainly eats fruit, but does supplement with leaves and occasionally invertebrates and small vertebrates.
58
Allopatric speciation
* Allopatric implies that two different populations have geographical ranges that do not overlap.
* Reproductive barrier forms between two populations with geographically different ranges.
* Large scale geographical barriers because of topographical or climate change.
* Small scale geographical barriers because of local variation in the habitat of a slowly dispersing species.
59
Evolutionary sequence & brain size
| IMPORTANT
• 7-8 MYA:hominin/hominid lineage split from chimpanzee lineage.
• Pan troglodytes (chimpanzee) brain size today 300-400 cm3.
• Pan paniscus (bonobo) brain size today 300-400 cm3 .
• 7 MYA: Sahelanthropus tchadensis brain size 320-380 cm3.
• 4.4 MYA: Ardipithecus ramidus [ARDI] brain size 300-330 cm3.
-Discovered by professor tim white in integrative biology
- discovered in december 2009
- first signs of walking and climbing up trees
• 3.2 MYA: Australopithecus afarenesis [LUCY-PARTIAL BIPEDALISM] brain size 400-500
cm3.
• 2.5 MYA: Homo habilis brain size 600 cm3.
• 1.8 MYA – 200,000 YA: Homo erectus brain size 680-1100
cm3 and its offshoot clades in Africa and Europe.
• 400,000 – 28,000 YA: Homo neanderthalensis brain size similar to Homo sapiens.
• 200,000 YA - present: Homo sapiens brain size 1350 cm3
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Proposed Homo evolution scenarios:
* H. erectus > H. heidelbergensis > H. neanderthalensis
| * H. erectus > H. rhodesiensis > H. sapiens
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Homo erectus
* “Turkana Boy”skeleton is dated at 1.3 million years old was found near Lake Turkana in Kenya and represented a 5’3 inch boy estimated to be 13 years old.
* “Peking (Beijing) Man”skeleton discovered in China is estimated to be 500,000 years old; other skeletal remains of Homo erectus dating back 1.4 million years have been found in China.
* “Java Man”skeleton discovered on island of Java, Indonesia dated at 1.7 million old.
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Denisovans
* Denisovans are proposed to represent a group that shares a common origin with Neanderthals
* May have been widespread in Asia and Europe during the Late Pleistocene epoch
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Homo floresiensis
* Alternative argument has presented the possibility that the specimen represents a small bodied and microcephalic modern Homo sapiens.
* Another alternative argument suggests that the remains represent a Homo sapiens affected by endemic cretinism because of low iodine levels.• Alternative argument has presented the possibility that the specimen represents a small bodied and microcephalic modern Homo sapiens.
* Another alternative argument suggests that the remains represent a Homo sapiens affected by endemic cretinism because of low iodine levels.
64
Advanced bipedalism in
| Homo sapiens
* Knee allows the leg to straighten and the knee to lock which minimizes energy expenditure in supporting the body when standing upright.
* Humans have an angled femur and a change in the limb-moving muscles such as a gluteal abductors which enables legs to more easily spread apart.
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Fossil hallmarks of advanced bipedalism
* Positioning of the foramen magnum, which becomes more central as the posture becomes more upright and the skull must be supported by the spinal column.
* Changes in pelvis, hip socket, and femora
66
Human bipedalism
* Humans have a pelvic and muscular structure which allows the center of gravity to shift only slightly on each step, unlike the chimpanzee, which waddles back and forth with a shift of center of gravity with each step.
* The ability to run first emerged in the Homo genus, and modern humans can not only sprint, but also can endure long distance running.
67
Costs of bipedalism
* Backpain: the upright walking position creates pressure on the intervertebral discs, vertebrae, and the sacroiliac joints.
* Prolapse of disc, with injury to the lumbar or sacral nerves innervating the lower limbs, leads to pain, paresthesia, and sometimes motor dysfunction.
* Obesity increases likelihood of backpain
* The upright posture makes injurious falls more typical in aging people with unsteady gait and declining vision.
* Osteopenia and osteoporosis increases risk of femoral neck fractures in older populations.
* In order to walk upright in a bipedal fashion, the shape of the pelvis is changed with a flattening of the pelvis and a narrowing of the pelvic canal.
* Since Homo sapiens have a significantly larger brain than its hominin ancesters, delivery of the newborns head through the narrow pelvic canal can be problematic in some women.
68
Larger body size
* Increased body size and brain size increased nutritional energetic needs which required individuals to expand their ranges for foraging.
* Homo sapiens increase in height and body size enabled them to be able to forage longer distances
* Exposure to potential predation may have also contributed to selection for a larger and taller body size to enhance the ability to run and climb faster to escape.
69
Changes in hominin/hominid face, jaw, dentition compared to modern apes
• Flatter face.
• Teeth tucked under face with less protuberant jaw.
• Incisors became less prominent, canines become
smaller, and molars became larger.
• Change to a relatively L-shaped mandible.
• Less developed masseter muscles.
• Smaller zygomatic arch.
• Less developed masseter muscles and smaller zygomatic arch result in less powerful chewing action.
• Change in jaw shape and dentition resulted in a more grinding type of mastication to chew fiber-rich food
70
Costs of changes in hominid face, jaw, and dentition compared to modern apes
* It has been suggested that in recent centuries human infants, toddlers, and children in economically developed countries have been fed on particularly soft fiber-poor foods which has reduced the need for grinding movements and has increased risk of dental malocclusion and reduced development of mandible and maxilla causing increased impaction of wisdom teeth
* Evolutionary pathway is cultural evolution • Evolutionary pathway is mismatch with ancestral die
* The flattening of the face and the change in posture have changed the position of the eustachian tubes making it more difficult for fluid to drain from the tubes into the back of the throat
* This has resulted in an increased risk of otitis media (infection of tympanic membrane and middle ear).
* Evolutionary pathway is evolutionary anatomical constraints
* The changes in the position of the larynx to enable vocalization are associated with increased risk of sleep apnea.
* Evolutionary pathway is evolutionary anatomical constraints.
71
Reduced body hair on humans
* A hypothesis that is more plausible is that the hairlessness evolved by sexual selection.
* Pubic hair only appears at puberty and in both sexes the full pattern of sexual hair would be an indication of sexual maturity.
* Facial hair on males could also be an indication of sexual maturity.
* In females, breast development and menses could also indicate sexual maturity.
* Evolutionary pathway is sexual selection13
72
Encephalization quotient (EQ)
• Allometric calculation of the relationship between brain mass and body mass.
• EQ = brain weight/0.12(body weight)2/3.
• Chimpanzee EQ = 2.0
• Austalopithicenes EQ = 2.5
• Homo erectus EQ = 3.3
• Homo sapiens EQ = 5.8
• This progressive enhancement of brain
size suggests positive selection for increased brain size.
73
HARs
* HARs (human accelerated regions) are genomic regions showing accelerated rates of base substitution since the human/chimpanzee divergence.
* HAR1F (F stands for forward transcript) codes for an RNA molecule that is expressed in the fetal neocortex during development, and is co-expressed with a protein responsible for specifying cortical structure.
* The specific expression of HAR1F and rapid evolution of the human lineage suggest that it plays a role in the development of the highly expanded neocortex that is a unique human characteristic.
74
MCPH1 (gene microcephalin)
* MCPH1 (gene microcephalin) is an important regulator of brain size and appears to promote the proliferation of neural progenitor cells.
* Defects in this gene in humans can cause severe reduction in brain size.
* The rate evolution of MCPH1 has dramatically accelerated in the evolutionary lineage leading from ancestral primates to humans.
* These observations suggest that molecular evolution of MCPH1 may have contributed to the expansion of the brain size in the human lineage.
75
HACNS1
* HACNS1 appears to regulate genes involved in limb development, especially limb-joint regions and anterior parts of forelimb and hindlimb buds.
* It appears that the human-specific sequence changes in HACNS1 contribute to the unique human digit and limb patterning, including the opposable thumb and possibly also modifications in the ankle and/or foot that allow for efficient bipedalism.
76
GBX2
• A nearby gene, GBX2, encodes a transcriptional regulatory protein that is expressed in developing limbs
77
Increased brain size enabled Homo species to develop the following
* Language
* Find adaptive advantage in social interactions within their group
* Enhanced tool making abilities
78
Feed forward loops in cognitive development and
| selective pressure for increased brain size
```
Rising social complexity.
-
Greater intelligence.
¯
Development of more sophisticated technology.
¯
More complex ways of living.
¯
More sophisticated social structures.
¯
Increased need for higher cognitive function.
¯
Development of language permitted and expedited the increasing neural complexity.
```
79
Types of intelligence
* IQ = intellectual quotient
* EQ = emotional quotient
* SQ = social quotient
80
Traits unique to humans
* Large brain size.
* Craniofacial morphology.
* Complex behavioral and cultural traits.
* Vertebral, limb and digit innovations.
* Bipedal upright walking.
* Pelvic anatomy.
* Reduced hair cover.
* Many of the DNA-level changes responsible for unique human innovation involve multiple genes.
81
The origins of life
* Earth is around 4.5 billion years old.
* The earliest fossil record of bacteria is dated to about 3.6 billion years ago.
* The first eukaryote (cell with nucleus) evolved between 2.7 & 1.5 billion years ago.
* The first multicellular organism appeared 640 million years ago.
82
Gene
unit of heredity, DNA
83
Gene frequency
what percentage of the individuals in the population have this gene
84
Biological evolution:
occurs when there is a change in gene frequency in a population over time
85
Genome
• The entire complement of DNA sequences in a cell or organism.
86
Genotype
* The set of genes possessed by an individual organism.
| * May refer to an organism’s genetic composition at a specific locus or set of loci under consideration.
87
Allele
* One of multiple forms of the same gene, presumably differing by a mutation of the DNA sequence.
* Alleles are usually recognized by their phenotypic effects.
88
Evolution steps
| IMPORTANT
• Step 1: The origin of genetic variation
by random mutation or recombination followed by
• Step 2: changes in frequencies of alleles and/or genotypes, caused by natural selection and/or random genetic drift
89
Recombination
* Individuals inherit their genes and not their genotype from their parents.
* The meiotic cell division that forms the male and female gametes in sexually reproducing organisms involves two processes (recombination and assortment/segregation) which shuffle parental alleles into a unique combination in each egg or sperm.
* Every egg produced by a female and every sperm produced by a male are unique.
90
Two processes in meiosis which shuffle genes
1st is recombination during which homologous chromosomes exchange segments of DNA sequence, thereby creating new allele combinations on each chromosome.
• 2nd is independent assortment/segregation
of chromosomes into haploid gametes.
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Genetic Drift
Random changes in frequencies of alleles and/or genotypes within a population.
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Evolution
Natural selection or/and random genetic drift over generations produces change in composition of frequencies of alleles and/or genotypes in a lineage
93
Genotype frequency
• The proportion of the population with a specific allele pair at a particular locus
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Convergent evolution
• Evolution of similar features independently in different evolutionary lineages, usually from different antecedent features or by different developmental pathways.
95
Human examples of convergent evolution
* Lighter skin color has appeared to have arisen through different biochemical pathways in Europeans and East Asians.
* Lactase persistence in adulthood has arisen through different genetic pathways in Europe, East Africa, and the Middle East.
* Sickle cell hemoglobin has emerged independently in Africa and India
96
```
Artificial selection
(= selective breeding)
```
* Selection by humans of a deliberately chosen trait or combination of traits in a (usually captive or domesticated) population.
* The human breeder of animals or plants is the active agent that directs selection for a characteristic to change in the population for a specific purpose.
* Dog breeds ranging from chihuahuas to great danes and St. Bernards have been artificially selected for from wolves by humans.
* Hundreds of cultivars of apples have been developed through artificial selection by humans.
* Gene-editing through the CRISPR-Cas9 could be considered within the realm of artificial selection
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Four necessary conditions for natural selection
```
• Variation in reproductive success (fitness)
• Variation in the trait of interest
• Nonzero correlation between the trait
and reproductive success
• Trait is heritable
```
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Natural selection is not random
* While mutational and recombination events are random, natural selection is not.
* Natural selection can result in change of gene allele frequency that generates traits that increase fitness.
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Adaptation
• A process of genetic change in a population whereby, as a result of natural selection, the average state of a character becomes improved with reference to a specific function, or whereby a population is thought to have become better suited to some feature of its environment.
100
Positive selection
Selection for an allele that increases fitness.
101
Negative selection
A disadvantageous allele is lowered in frequency and perhaps entirely eliminated.
102
Balancing selection
* Number of selective processes by which multiple alleles (different versions of a gene) are actively maintained in the gene pool of a population at frequencies above that of gene mutation.
* An example of balancing selection is heterozygote advantage where an individual who is heterozygous at a particular gene locus has a greater fitness than a homozygous individual e.g., people who are carriers of the sickle cell allele.
103
Individual selection
* The individual is the most important unit on which selection acts.
* A form of natural selection consisting of nonrandom differences among different genotypes (or phenotypes) within a population in their contribution to subsequent generations.
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kin selectioin
form of group selection
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Inclusive, direct & indirect fitness
* In 1964, William D. Hamilton introduced the concept of inclusive fitness of an allele, its effect on both the fitness on the individual bearing it (DIRECT FITNESS) and the fitness of genetic relatives that carry copies of the same allele (INDIRECT FITNESS).
* An individual organism has inclusive fitness, with both direct and indirect components.
* Selection based on inclusive fitness is called kin selection because these other individuals are the bearer’s genetic relatives (kin).
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Inclusive fitness
• Sum of direct and indirect fitness
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Altruistic behavior
• Behavior in which one individual helps another, seemingly at its own risk or expense.
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Hamilton’s Rule IMPORTANT
* An altruistic trait can increase in frequency if the benefit (b) received by the the donor’s relatives, weighted by their relationship (r) to the donor, exceeds the cost (c) of the trait to the donor’s fitness.
* Altruism spreads if br > c
109
Intrasexual competition
* Intrasexual competition between members of the same sex (usually male-male).
* Intrasexual selection drives the selection of attributes that allow alpha males to dominate other males to gain breeding rights to females in the group.
* Some deer species fight with their antlers to gain mating rights over females in the herd.
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Intersexual competition
* Intersexual selection favors traits that improve mating success even if they decrease individual health or survival.
* For example a male peacock’s long colorful feathers improves his reproductive success by being more attractive to females but reduces his chances for survival because he moves more slowly and can not fly.
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Mate choice (Intersexual selection)
* Women are attracted to scents of men who are most unlike themselves in major histocompatibility complex genes (MHCs)
* Human mate pairs with similar MHCs tend to be less fertile with higher miscarriage rates
* The more dissimilar the MHCs of a human male/female pair, the better their offspring immune systems will be at detecting foreign proteins, e.g., viruses or toxins
112
Neutral selection
Change in gene frequency generated by random processes that produces phenotypic variants that do not differ in their effect on reproductive success, that is, when their variation is neutral compared to fitness.
113
Mechanisms causing random change that drive genetic drift
* Neutral variation in reproductive success
* Mendel’s Law of Segregation states that there are two alleles present at a locus in a heterozygote diploid organism, and the probability that one of them will get into a given gamete is 50% (flip of a coin)
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Bottleneck
A severe, temporary reduction in population size.
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Founder effect
The principle that the founders of a new small population carry only a fraction of the total genetic variation in the source population.
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Genetic drift
Random changes in the frequencies of alleles or genotypes within a population.
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Causes of Bottlenecks
* Migration
* Infectious Disease
* Predation
* Famine
* Environmental catastrophe • War or genocide
* Cultural isolation
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Genetic drift
In small populations, in the absence of selection, random variation in allele frequencies from genetic drift can cause the allele either to disappear (0% frequency in the population) or become fixed (100% frequency in the population).
- The changes due to genetic drift are not driven by environmental or adaptive pressures, and may be beneficial, neutral, or detrimental to reproductive success.
• Fairness in meiosis and neutral variation in reproductive success drive genetic drift
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Finnish founder population
* The Finnish population is a highly isolated population formed approximately 2,000 years ago by a founder population characterized by low population count, relative homogeneity, and isolation.
* Through a bottleneck migration, the Eastern Finnish population is estimated to have been founded by only 20-30 families.
* Although a rapid population increase occurred, the Finns in this area remained a highly homogenous population.
* Several mutations can cause this disorder, however, 98% of the cases in Finland have the identical mutation which suggests that almost all Finnish cases arise from a single founder event.
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Interaction between drift & selection
* In a finite population size, allele frequencies may be simultaneously affected both by selection and chance (drift).
* The effect of random genetic drift is negligible if selection on a locus is strong relative to the population size.
* Genetic drift is predominate if selection is weak on a locus.
* Genetic drift is usually predominate when populations are small.
* Deleterious mutations can become fixed (100% frequency in the population) by genetic drift, especially if selection is weak and the effective population size is small.
* A slightly advantageous mutation is less likely to be fixed by selection if the population is small than if it is large, because it is more likely to be lost simply by chance.
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Acclimatization
* Acclimatization occurs in a short period of time (days, weeks, or months) and within the organism's lifetime.
* Acclimatization to high altitude continues for months or even years after initial ascent, and ultimately enables humans to live more comfortably in this environment.
* Humans who migrate permanently to a higher altitude naturally acclimatize to their new environment by developing an increase in the number of red blood cells to increase the oxygen carrying capacity of the blood, in order to compensate for lower levels of oxygen in the air.
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Spandrel
* Spandrel is a phenotypic characteristic that is a byproduct of the evolution of some other character, rather than a direct product of adaptive selection.
* An example is the human nose evolved for breathing and regulating air temperature, but a by-product of this evolved structure is its ability to hold up eye glasses.
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Exaptation
* Gould introduced the term exaptation referring to a trait that currently performs a particular function but originally arose as an adaptation for another function.
* An example is feathers on birds probably evolved as insulation in reptilian ancestors but were later exapted for flight.
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Speciation
• Evolution of reproductive isolation within an ancestral species, resulting in two or more descendent populations.
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Types of speciation
* Allopatric
* Sympatric
* Peripatric
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• Allopatric
• Allopatric implies that two different populations have geographical ranges that do not overlap.
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Sympatric
• A population diverges into two reproductively isolated populations without the existence of a geographical barrier preventing mating between the two groups.
• A mechanism for sympatric speciation may be, for example, a sub-population that becomes particularly well adapted to procuring a particular food resource, thus creating ‘specialists’in relationship to a particular food resource which may outcompete generalists for the resource.
exp: darwins finches
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Peripatric speciation
* Peripatric: Population peripheral to most of the other populations of a species.
* Peripatric speciation: Speciation by evolution of reproductive isolation in peripatric populations as a consequence of a combination of genetic drift and natural selection.
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Gradualism
• The proposition that large differences in phenotypic characters have evolved through many slightly different intermediate states.
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Punctuated equilibrium
the hypothesis that evolutionary development is marked by isolated episodes of rapid speciation between long periods of little or no change.
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Phyletic gradualism
is a model of evolution which theorizes that most speciation is slow, uniform and gradual.
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Hominid timescale
| IMPORTANT
* Paleolithic age (stone age): 2.5 million years ago to 10,000 years ago.
* Neolithic age (late stone age with emergence of plant and animal domestication): 10,000 - 4,000 years ago.
* Bronze age (metal tools widely used): 5,300 - 2,400 years ago.
* Iron age: 3,300 - 1,600 years ago.
* Silicon age: 1971 - present
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Newborn delivery solution to trade-off of having a narrower pelvis
for bipedal walking
* Other apes are precocial, having relatively mature offspring at birth capable of some independent activity.
* So the human newborn head can fit through the relatively narrower pelvic cavity, humans are born ‘early’, have developed secondary altricial characteristics and are extremely dependent on parents for a long period after birth.
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Regulation of fetal growth and maternal constraint
* Maternal constraint in pregnancy includes the limitations to the capacity of how much the utero-placental unit can supply nutrients to the fetus.
* Hence, fetal growth is not solely controlled by genetics, but rather a combination of fetal genetics and the intra-uterine environment.
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ABO system
* The ABO system is the most important blood-group system in determining appropriate donors and recipients for human-blood transfusions.
* ABO is transmitted through monogenic inheritance.
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ABO system
• Humans may have the same blood type phenotype (characteristic) but different genotypes (gene sequences)
• Three blood type alleles: A, B, & O
• Each human has two of these alleles
• A or B are each dominant over O which is recessive, but
neither A or B are dominant over each other
• Six possible genotypes: AA, AO, BB, BO, AB, OO
• Four blood types/phenotypes: A, B, AB, & O
• AA genotype: phenotype A
• BB genotype: phenotype B
• AB genotype: phenotype AB (universal recipient)
• AO genotype: phenotype A
• BO genotype: phenotype B
• OO genotype: phenotype O (universal donor)
• Depending on the person’s blood type, they may develop anti-A antibodies, anti-B antibodies, or no antibodies.
• Anti-O antibodies are NOT formed by humans.
• Persons with the genotype AA, AO, or OO will form anti-B antibodies if they are exposed to blood from a person with a BB, AB, or BO genotype, causing them to rejection the blood.
• Persons with the genotype BB, BO, or OO will form anti-A antibodies if they are exposed to blood from a person with a AA, AB, or AO genotype, causing them to rejection the blood.
• Persons with genotype OO will form both anti-A and anti-B antibodies when exposed to both A and B alleles
• Persons with genotype AB form no antibodies
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Universal recipient
| Universal donor
AB
| OO
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Blood phenotype B has some protection against cholera
cholera
