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Sem 2: Evolutionary biology > Week 11 > Flashcards

Week 11 Flashcards

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1
Q

Where you place humans on the tree of life?

A

Primate phylogeny -> numerous derived characteristics
Clearly most related to great apes (hominidae)

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2
Q

When did the branch leading to humans split off of tree of life?

A

Consensus from many independent gene sequences
Human most related to chimps
Molecular clock - separation 5.4 mya

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3
Q

What are the Homini?

A

Humans, extinct ancestors and related races/species

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4
Q

How many taxonomic groups within great apes?

A

Within the great apes (Hominidae) – four taxonomic groups (tribes)
Orangutans, gorillas, chimpanzees and humans.

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5
Q

What is an overview of the oldest hominins?

A

Oldest – Sahelanthropus tchadensis
Discovered in Chad, central Africa – ca 5-6 Mya

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6
Q

What are examples of other hominin forms?

A

Homo Habilis
Homo erectus
Homo heidelbergensis

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7
Q

What is an overview of the hominini despersal?

A

Homo genus range expansion out of Africa approx 1.8 MYA
Homo erectus like forms (archaics) spread across the world
Resolving between these species remains controversial

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8
Q

What was an overview of the different forms between the different forms around the world?

A

Recent evidence suggest that different forms were members of a single species
H. erectus - a very successful species – surviving 1.8 million years
Modern humans – only very recent

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9
Q

What makes us human?

A

Use of complex tool industry is the definition of humans (homo)
Increased cognitive abilities - brain size
H. erectus developed tool and cultural technologies
Advances may have lead to expansion of Homo species across the globe 1.8 Mya

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10
Q

What are potential key drivers for human cognitive abilities?

A

Feedback loops caused by tool use and/or social interactions between species

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11
Q

What is the evolution of bipedalism?

A

Footprints - Australopithecus afarensis - 3.3 Mya
Seen in upright bipedal, free striding gait – well developed arch to the foot

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12
Q

Why did bipedalism evolve?

A

Frees the hands for fine manipulations
Greater stamina for long distance travel
More effective hunting
Improved ability to carry food

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13
Q

What is the evolution between bipedalism and human habitats?

A

Many theories link bipedalism to living in a savanna – where A. afarensis lived but prior to this A. anamensis (4mya) – thought to be bipedal - existed in dry woodland

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14
Q

What are the differences between humans and other great apes?

A

Gorillas, Chimps, n = 24 chromosome pairs
After split from chimps, 2 chromosomes fused (12 and 13)
Humans n = 23

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15
Q

What is the genetic differences between humans and other great apes?

A

1% if focus on coding sequences in genome
5% all regions (incl insertions and deletions)

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16
Q

Which genes make us human?

A

80 genes in chimps – disabled in humans
Functional differences in genes related to sensory perception, immune defence, spermatogenesis

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17
Q

In key organs what are the differences between human and chimp compared to rhesus monkey?

A

Blood human and chimp equidistant to rhesus
Liver human slightly more diverged than chimp
Brain human massively diverged compared to chimp

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18
Q

Where did humans evolve?

A

Generally agreed – evolved in east Africa
But Henn et al 2011 PNAS. >500,000 markers – indicates S. African origin?

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19
Q

What are the two origins of modern humans?

A

Out of Africa
Multi-regional evolution

20
Q

What is an overview of out of Africa theory?

A

Emerged recently in Africa – spread and replaced archaics

21
Q

What is an overview of multi-regional evolution theory?

A

Hominin populations - evolved in situ into modern
homo populations – with gene flow between
Implies ancestral forms = not biological spp

22
Q

Which theory for the human evolution was correct?

A

Fossil evidence could not refute multi-regional evolution hypothesis
Genetic/genomic evidence indicates there was recent expansion & replacement by H. sapiens
Out of Africa theory

23
Q

Did non-African archaics contribute to the gene pool of modern humans that expanded into each region?

A

2% Neanderthal DNA in non-African Humans
4-6% Denisovan DNA in Melanesian humans

24
Q

What is an overview of the Origin of Humans?

A

Humans – demographically young species
From east or south Africa – ca. 100,000 years ago
Recent expansion - with small sequential colonisation events

25
Q

What is the relationship between H.sapiens and other hominins?

A

Replaced archaic forms of hominins – with some inter breeding
H. Sapiens – lone survivors of extinct radiation of bipedal African hominins

26
Q

What is the effective population size of humans?

A

Approx 10,000

27
Q

What is the genetic variation between humans?

A

6 % sequence divergence
All humans – closely related!

28
Q

How has genetic variation of humans measured?

A

mtDNA – pairwise comparison between random individuals within each species

29
Q

What is the genetic variance of other great Apes?

A

Gorrillas - 22%
Bonobos - 11%
Western chimpazee - 16%

30
Q

What is the FST for humans?

A

Genetic variation – Fst between populations
Worldwide Fst = 0.15;
so 80% of variation found within populations and only 20% among populations

31
Q

What is an overview of the genetic variance between humans?

A

Human genetic variation cannot be subdivided into sharply defined discrete races
Most of what variation there is was left in Africa

32
Q

What can determine genetic differences between populations?

A

Subtle differences exist in alleles frequencies at specific loci between populations.
Accumulated - determine statistical genetic differences between populations

33
Q

What are examples of the eight classes of genetic similarity?

A

Western and Southern Europe + Africa
Northern Europe + Eastern Europe + Iran
Australia

34
Q

What are fine scale examples of genetic structure in the UK?

A

Distinct unique genetic groups in Cornwall, Devon, Northern Wales, 2 in southern wales

35
Q

What is gene flow like since human expansion?

A

Global Fst – 0.15 - low levels of gene flow since human expansion
Ca. one individual per generation between continents
No obstacle to changes being caused by selection

36
Q

How did they prove that humans are still under selection?

A

Expected distribution of Fst of loci across the genome because of drift (without selection) vs observed distribution
More loci with higher Fst’s than expected = identifies genes under selection

37
Q

What is an example of human evolution of a key trait?

A

Lactose tolerance

38
Q

What is an overview of the relationship humans have with lactose ?

A

Lactose – nutritional carbohydrate in milk
Broken into glucose/galactose by Lactase
Only active up to weaning age in other mammals
Most humans (70%) cannot digest Lactose – intolerant to large amounts of unfermented milk

39
Q

What is the histroy of the evolution of lactose tolerance?

A

Persistence of lactase into older age – Northern European populations
Polymorphism upstream of the LCT gene – associated with lactase persistence
Frequency of the polymorphism – matches geographical distribution of dairy production

40
Q

What caused the ability to tolerate lactose?

A

Lactase persistence allele – In European humans, = recently single mutation
Found in haplotypes (sections of linked genes) that are homogenous over long sections of genome – recombination hasn’t had time to break up ancestral sequence

41
Q

When was the rough origin of the mutation for lactose tolerance?

A

Length of haplotype – consistent with origin of this variant 10,000 years ago
Roughly when dairy cattle farming became established in Europe

42
Q

What is the overview of human skin colours?

A
  • Dark skin = ancestral in humans – protects against Ultra-Violet radiation (UV)
    But some UV – required – for synthesis of Vitamin D
    Pale skin evolved – avoids Vitamin D deficiencies at higher latitudes
    Skin colour closely related to regional levels of UV
    Alleles at various specific pigmentation loci – closely associated with light skin
43
Q

What is an example of human evolution occuring today?

A

Influence HIV/AIDS has on human evolution

44
Q

What is the overview of HIV on current human evolution?

A

Some geneotypes make a person more susceptible to HIV compared to others
The more susceptible the reduced number of children compared to genes that offer resistance

45
Q

How does population level of HIV impact evolution of resisitance genes?

A

In South Africa - 20% pop have HIV
Most common susceptible genotype - 0.8 children
Most common resistant genotype - 1.3 children

Other South African population lower amount of HIV
Most common susceptible genotype - 0.97 children
Most common resistant genotype - 1.1 children

South African population with higher amount of HIV
Most common susceptible genotype - 0.7 children
Most common resistant genotype - 1.38 children

There is stronger selection in populations where HIV is more prevalent

Sem 2: Evolutionary biology (11 decks)

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