Lecture 13 - Evolution Flashcards
1
Q
How did the Galapagos Islands in Ecuador influence Darwin’s theory?
A
- Darwin visits in 1835
- Geologically young island
- High number of endemic species
- Darwin notices that mockingbirds differed between islands
- Takes back a samples of mockingbirds and finches for further study
2
Q
What is functionalism?
A
- Characteristics of an organism has a useful function – all for survival e.g. bones of the forelimb
- To understand physiological basis of various behaviours (how), we must first understand what these behaviours accomplish (why)
3
Q
What are the mechanisms of natural selection?
A
- Differences are seen within species and inherited by offspring
- Favourable characteristics that have help in survival and reproduction, get passed on to offspring (unfavourable ones die out)
- Over generations, these characteristics become dominant
- Mutations (accidental errors) could occur. Non useful die out, favourable passed onto offspring
- Drives adaptive radiation
4
Q
What is adaptive radiation?
A
- Single species rapidly evolves into multiple new species to match survival
- Little competition and diverse resources (e.g. islands)
- Example: Darwin’s Finches
- Common ancestor first arrives
- Different islands have different resources
- Natural selection – beak shapes to food source
- Over time, multiple new species evolved
5
Q
What is the timescale of human evolution?
A
- Warm blooded animals survived because they had warm blood
- Other animals then adapted
- Humans a relatively young species
- Humans are hominids
- Gibbons are hominoid not hominid
6
Q
A brief history of human evolution
A
- Earliest mammals – small nocturnal predators that fed on insects
- The first hominids (humanlike apes) appeared in Africa
- First hominid to leave Africa around 1.7 million years ago
- Human evolution was a relatively late development – given overall timescale of primate evolution (some 60 million years ago)
- Rapid evolution of human brain and behaviour sets us apart but also seen as part of the evidence for our animal ancestry
7
Q
Describe existing relatives of humans
A
- Our closest living relatives – Chimpanzees, Gorillas and Orangutans
- DNA analysis – very little difference between these 4 species
- Example: Humans and chimpanzees share almost 99% of their DNA
8
Q
Does size matter (human brain evolution)?
A
- Large body = large brain?
- Elephant brain = 0.2% of total body weight
- Human brain = 2.3%
- Shrew = 3.3%
- Answer: No need, neurons and complexity are key
- Human useful functions and need for complex brain:
- Bipedalism – mobility, energy efficiency and adaptability (go further distances)
- Opposable thumbs – agile hands for tool use (hunting/gathering)
- Colour vision – differentiate fruits from leaves, fruit decay
- Linguistic abilities – sharing information, propagation of species
9
Q
Describe human brain evolution
A
- Herculano-Houzel et al. (2007) – brain weight to number of neurons, found primates to have most neurons
- Changes in neocortex size compared to other non-human animals (including non-human primates)
- How are large brains achieved? How are neurons coded for useful functions and cognition?
- Answer - Neoteny
10
Q
Describe human brain development
A
- Neoteny – slowing of maturation, allowing for time for growth, important for large brain and complexity
- Not all neurons are coded at birth, allowing for learning based on environment
- Human brain weight for a neonatal = 350g
- Adult human brain = 1400g (neurons coded for environment based learning)
11
Q
Why do we study non-human species?
A
- Similarities across species in brain structure and function allow the use of animal models to understand brain-behaviour relations
- Understanding mechanisms (e.g. planes based on bat flight)
- Models of neurological disorders
- Comparative studies:
- Particular species have advantages
- Study evolution of the brain
12
Q
What is the importance of animal models?
A
- Hippocampal lesions in rats impaired conditioning to contextual cues (Maren et al., 1997)
- Amnesia in humans with hippocampal damage
- Rat studies tell us which neuronal systems are key
13
Q
What is the importance of comparative studies?
A
- Clayton (1998)
- Unique source of evidence for the role of hippocampus in learning and memory
- Within birds and mammals - hippocampal volume is enlarged in food storing species (remember where they’ve stored food and how to get there)
- Hippocampus can change size in response to experience
14
Q
What is game theory?
A
Von Neumann & Morgenstern
- Theory of Games and Economic Behaviour (1944)
- Classic definition: mathematical model of strategic decisions
- Analysis of outcomes based on their own decisions and other players decision
- No control on others’ decision
Maynard Smith & Price
- The Logic of Animal Conflict (1973)
- Applied in understanding evolution strategies
- Evolutionary Stable Strategies (ESS) and Price Equation
15
Q
Describe the hawk-dove game
A
- Cooperation vs. conflict
- Hawk: aggressive and will take by force (fight) if necessary
- Dove: passive and will avoid conflict or share
- Both encounter a food resource = 1
- Benefit of acquiring resource
- Cost of fighting/risk of injury
16
Q
What are the possible outcomes in the hawk-dove game?
A
- Hawk meets Hawk: fight for resource. Winner gets resource but there is a cost of injury
- Hawk meets Dove: hawk dominates, takes resource
- Dove meets Hawk: hawk dominates, takes resource, dove gets nothing
- Dove meets Dove: both are passive so share resource. Each get ½ resource
- Which is best for survival?
17
Q
What is an Evolutionary Stable Strategy (ESS)?
A
- Once adopted by most of the population, cannot be invaded by alternative strategy
- Best strategy for survival (needs to be ESS)
- Two Conditions:
- Strategy should do better with itself than any new competing strategy if it tried to invade
- Strategy should have at least comparable pay off (benefit) than any other strategy
18
Q
Describe the hawk-dove game and ESS
A
- In isolation BOTH Hawk and Dove strategies violate condition 1:
- Hawk strategy –
- Hawk vs. Hawk – fight and injury
- Hawk vs. Dove – hawk wins resource
- Dove strategy –
- Dove vs. Dove – peacefully share
- Dove vs. Hawk – hawk wins resource
- Mixed strategy would work best as this is stable
- Purely competition or purely cooperation strategy not useful (need mixed)
19
Q
What is the prisoners dilemma?
A
- Prisoners 1 and 2 arrested for the same crime. Interrogated separately and cannot communicate. Choices offered are:
- If both stay silent = both get 1 year each
- If one confess (implicates other) while other stays silent = betrayer is free, silent player gets 5 years
- If both confess (implicates other) = each get 3 years
- What is the best strategy?
20
Q
What is the paradox in the prisoners dilemma?
A
- Best strategy for mutual benefit = both stay silent (1 year each)
- Best strategy for each prisoner individually = confess and implicate the other (0 years)
- Without knowing the other prisoner’s strategy (no interaction) = best strategy is still to confess and implicate
- The more number of arrests, to defect is of more benefit
21
Q
What is Axelrod and Hamilton’s (1981) tit for tat strategy?
A
- Biological interactions – assumption is that the same two individuals will meet more than once
- Best strategy for mutual benefit = staying silent
- Cooperation evolves when Tit for Tat Strategy is employed
- If in Round 1, Prisoner 1 confesses, then Round 2, Prisoner 2 confesses
- Tested using computer simulation – cooperation emerged as ESS when probability of two individuals meeting was high
22
Q
What is altruism?
A
- Definition: behaviour at a cost to oneself but benefit to others (Fehr & Fischbacher, 2003)
- Contrary to natural selection?
- Survival of the fittest – not “strongest” but best at passing on genes
- Those with higher fitness – have more offspring – more frequency
- So, why help others if it costs you? (use game theory to explain altruism)
23
Q
Describe kin altruism (altruism towards relatives)
A
- Inclusive Fitness: includes both direct fitness (offspring of an individual) and indirect fitness (offspring in the same species)
- Hamilton’s Rule (Hamilton, 1963) : rB>C (r = genetic relatedness, B = benefit to recipient and C = cost to altruist’s fitness)
- Price’s Equation: mathematically explains how natural selection is connected to inclusive fitness
- Even if there is a cost to individual fitness, if net effect (genetic line) increases (rB), altruism increases
24
Q
What is an example of kin selection?
A
- A meerkat stands guard while others forage
- Reduces guard’s individual survival chance/cost (C)
- Relatives benefit in the group (rB)
- Overall chances of survival increase (inclusive fitness)
- Therefore, ESS and evolves within the population
25
Describe non-kin altruism (why help strangers?)
- Based on two mechanisms:
- Reciprocal altruism (Trivers, 1971)
- Benefits will be reciprocated in a similar situation
- Price Equation – past cooperation predicts future fitness
- Iterated Prisoners Dilemma
- Group Selection
- More cooperation – helps dominate selfish groups
- E.g. humans giving to charity, vampire bats regurgitating blood for non-relative vampire bats (Wilkinson, 1984)
