Part 4 - Humans and Levels of Selection

Question 1

One controversy associated with evolutionary psychology/sociobiology is that it is often reduced to very … arguments, e.g. defined evolved gender roles.

Answer 1

Simiplistic

Question 2

It can be difficult or considered … to carry out certain tests on human subjects - hard to gather useful data.

Answer 2

unethical

Question 3

Another controversy that has arisen since the time of Darwin is the idea of …. Evolutionary theory has been used to justify ideologies such as … and ….

Answer 3

eugenics, apartheid, nazism

Question 4

A third controversy concerns …. When we exhibited certain behaviours we are not consciously considering its effect on our …. However, this is not true of any animal really (probably), e.g. a cuckoo chick pushing a reed warbler egg out of its nest is not considering its fitness benefits, they’re evolved behaviours that do not need to be rationalised.

Answer 4

motivation, fitness

Question 5

Why is menopause problematic?

Answer 5

Life history theory tells us that natural selection should synchronise the senescence of somatic and reproductive functions - why would the body remain functional long after reproduction stops?

Question 6

What is menopause?

Answer 6

The loss of reproductive potential and long post-reproductive life

• not exclusive to humans - found in 2 other organisms - shortfin pilot whales and killer whales.

Question 7

Menopause exists in every society, regardless of modern medicine. Across societies, the median age of a woman’s last birth is …. The average age for menopause is …. This leaves a post-reproductive life of generally over 20 years.

Answer 7

38, 50

Question 8

Pilot whales have a median age of last birth of 36 (similar to our own), leaving 30+ years of post-reproductive life. Killer whales are longer lived, with a median age of last birth of …, leaving up to … years of post-reproductive life.

Answer 8

48, 90

Question 9

What are the main hypotheses for the menopause?

Answer 9

a) mother hypothesis - to avoid risky reproduction and mortality in later life and ensure survival of existing offspring
b) grandmother hypothesis - kin selection - gain inclusive fitness by helping existing offspring to reproduce

Question 10

a) By collecting life-history data on pre-modern (before oral contraception and modern medicine) Finns and Canadians, Lahdenperä et al. (2011) found that … of children beyond age 15 was not affected by the age at which their mother died in canada, and in finland there was only a reduction in lifespan if the mother died when the child was between … years old (…-… age). In both populations, there was no effect of the child’s age when the mother died on lifetime reproductive success.

So evidence suggests that, beyond …, offspring fitness was not affected by maternal …. From this analysis, the mother hypothesis cannot explain the post-reproductive … of human females.

Answer 10

lifespan, 0-2, pre-weaning

weaning, death, longevity

Question 11

a) Why? It is likely … for by other family members.

Answer 11

compensated

• capacity for compensation reduced prior to weaning as this requires maternal resources

Question 12

b) Grandmother hypothesis - number of grandchildren should be correlated with…

Is this the case?

Answer 12

post-reproductive lifespan

There is a strong positive correlation - on average there are 2 extra grandchildren for every 10 years post menopause (across Finnish and Canadian populations)

• supports grandmother hypothesis

Question 13

b) found that a living grandmother was associated with:
- higher …
- higher …
- earlier …
- shorter birth …
- increased survival to …
in daughters

Only if grandmother was …
Younger grandmas had more of an effect.

Answer 13

fecundity,
LRS,
reproduction,
intervals,
15

local

Question 14

Grandfathers…

Answer 14

do not have the same effect - non-significant effect on lifetime reproductive success of daughters.

Question 15

Cant and Johnstone (2008) argued that the grandmother hypothesis is not the complete answer. This is because…

Answer 15

the kin-selected benefits of helping do not outweigh the benefits of continued reproduction.

Question 16

They suggest that menopause is also driven by…

Answer 16

reproductive competition between mother and daughters (and daughters in-law)

Question 17

Lahdenperä et al. (2012) also tested this hypothesis in their Finnish population. They found that there was very little overlap, at the population level, between the production of … and the production of …, i.e. mothers and their daughters very rarely overlap in their production of offspring.

Overlap of a mothers offspring with her daughter-in-law’s offspring…

Answer 17

children, grandchildren

reduced the survival of 1st and 2nd generation offspring (no effect when mother and daughter overlap reproduction)

Question 18

So a combination of the … effect and reproductive … between mothers and their daughters … … seems to provide a good explanation for the occurrence of menopause in humans.

There is evidence that similar processes are at play in the whales in which we observe menopause.

Answer 18

grandmother, competition, in law

Question 19

Are humans cooperative breeders?

Assessing Finnish populations again (Nitsch et al, 2013), a positive effect of…

Answer 19

number of elder siblings on survival to sexual maturity was found (particularly true of males and elder brothers on females)

• not a significant effect of number of elder sisters on female survivorship

Question 20

However, the number of elder same sex siblings an individual has has a negative effect on….

This may be because in many societies there is … inheritance of resources, meaning the more elder brothers you have, the fewer resources you will have when you come to reproduce yourself.

And in females, this may be because in many societies there is a wealth transaction when you get married, and younger siblings will have less chance of marriage and less money left over - fewer offspring on average

Answer 20

the number of offspring they produce

patrilineal

Question 21

Overall, fitness is increased by older …-… siblings, but reduced by older …-… siblings. This means there is no … effect of having siblings on an individual’s fitness - siblings are (probably) not ….

Answer 21

opposite-sex, same-sex, net, helpers

Question 22

Are aunts and uncles helpers?

Answer 22

A similar analysis bu Nitsch et al. (2014) reached the same conclusion (using data from the same population) - no net effect of having aunts or uncles on fitness

Question 23

A study by Pettay et al. (2016) used data from the same population to plot offspring survival for co-breeding wives against that of non-co-breeders. What was found?

Answer 23

Again, no/non-significant effect.

Question 24

From this Finnish population, at least, it appears there is little evidence for … … in humans, beside the … effect.

Answer 24

cooperative breeding, grandmother

• this is not necessarily true in all societies (read coursework paper)

Question 25

As in any other mammal, males have a higher … … than females.

Answer 25

reproductive potential

Question 26

The view that humans are monogamous is largely a western idea. If we look across 849 human societies across the world, we find that 0.5% are …, 16% are … and 84% are ….

Answer 26

polyandrous, monogamous, polygynous (prevailing mating system)

Question 27

Polyandry is practiced in small populations across the world, e.g. … and ….

These are … communities living at high … in harsh environments.

Typically there are 2-3 co-husbands per wife (usually …). 33% of males aged 10-59 were in polyandrous marriages. 31% of females aged 20-59 were unmarried. Unmarried women, on average, have 0.7 children, married women have, on average, 3.3

Answer 27

kashmir, tibet,

Buddhist, altitudes

brothers

Question 28

Why has this polyandrous system arisen in this environment?

Answer 28

Incredibly harsh environment (can reach -40 to -50C, very short growing season, little agricultural land). If land is split up between sons, resources would be very quickly depleted. It appears that polyandry is a strategy designed to avoid overexploitation of the environment.

However, muslim communities in this area of kashmir do not practice polyandry, so culture also influences mating system.

• Environment and culture dictates mating system.

Question 29

How is conflict within these polyandrous families controlled?

Answer 29

The fact that a woman marries brothers reduces conflict (kinship). At least raising nieces and nephews, even if they don’t produce any offspring themselves. There is also an age hierarchy (eldest brother marries usually in early twenties. Youngest brothers likely not of reproductive age yet. Also, often the second brother is sent to the monastery to become a monk.

Question 30

Monogamy is a common mating system in …-… societies. However, it may not be as common as it seems. Extra-pair paternity may be common and so may … monogamy.

Answer 30

hunter-gatherer, serial

Question 31

It is considered unethical to sample extra-pair paternity rates in human families.

An alternative way to assess this is by looking at the relationship between testes weight:body weight and EPP rate in other animals and comparing them with our own. Animals with high EPP rates generally have … testes:body weight ratios as they need to produce large quantities of sperm because of … ….

We find that human testes weight: body weight ratios are pretty average when compared with other animals, suggesting that EPP in human societies is not as common as in animals such as ….

Answer 31

higher, sperm competition, chimpanzees

Question 32

Jokela et al. (2010) looked at serial monogamy in the USA and found that…

Answer 32

in women it had no effect on lifetime reproductive success (av. number of children), but in men it increased with number of serial spouses

Question 33

Polygyny is a widespread marriage system (e.g. mormonism, Turkish harems). In most cases in such societies, it is only the wealthy who are able to have harems.

Data from the Kipsigis of Kenya shows that the number of reproductive wives is a function of…

Answer 33

area of plot land owned (acres) - i.e. wealth

Question 34

The existence of resource defence polygynuy has consequence in the form of financial transactions and in patterns of inheritance within societies.

In a survey of 1267 societies, 66% of marriages involved … payments (from groom’s family to bride’s family). Only 3% involved … payments (wife’s family to groom’s).

In … of highly polygynous societies, there were bridewealth payments - makes it important in these societies for males to hold resources, as otherwise they won’t be able to afford a wife. We see … favouring sons increasing as the marriage system becomes more polygynous. (See table on phone for all data)

Answer 34

bridewealth, dowry

91%, inheritance

Question 35

Human societies are more complex and operate at a much larger scale than those of any other organism.

Currie et al. (2010) investigated … transitions between social states across a huge number of societies across the western pacific, using language … to evaluate these transitions.

Their 4 categories for societies were:

• … - no leader. Kin groups without authority figures
• Simple chiefdom - a single chief without civil service or officers in an intermediate tier
• Complex chiefdom - there were intermediate levels of authority
• State

Answer 35

political, phylogeny

Acephalous

Question 36

They found that there were stepwise transitions from first listed above (acephalous - least complex) through to last (state - most complex), without any big jumps. However, there were commonly transitions in the reverse direction that sometimes did have big jumps (collapses in …, sometimes from state to acephalous). These collapses were often associated with…

Answer 36

complexity, ecological overexploitation (e.g. easter island)

Question 37

Increases in political complexity tend to be in … jumps. Decreases may either be in … jumps or in bigger jumps indicating social ….

Answer 37

sequential, sequential, collapse

Question 38

VC Wynne-Edwards was the last of the strong advocates for “old” group selection. He was a population ecologist and observed that animal fecundity was lower at higher density. The consensus was that this was due to density dependence, but he strongly argued that it was due to reproductive …-….

Answer 38

self-restraint

Question 39

These arguments were effectively demolished in the 60s and 70s by key thinkers such as…

Answer 39

George Williams and Richard Dawkins (aka the Dawkmeister)

Question 40

The key arguments in these against group selection suggested that the conditions for “old group selection” are unlikely to be met in nature. “In any population of … individuals exercising self-restraint, any … mutant that did not exercise self-restraint would be very … and would spread rapidly through the population”

Answer 40

altruistic, selfish, successful

Question 41

In theory, group selection can work if some groups die out … than others. However, individuals usually die at a … rate than groups, so individual selection will be more powerful.

Additionally, for group selection to work, groups must be … so that selfish individuals can’t migrate into cooperative groups.

Answer 41

faster, faster,

isolated

Question 42

In the last couple of decades, “new group selection” hypotheses have been proposed and advocated by people such as EO Wilson, Martin Nowak and David Sloan Wilson.

David Sloan Wilson conceptionalises selection as operating…

Answer 42

at multiple levels (a “russian doll” of levels of selection)

Question 43

How can “new” group selection models be made to theoretically work? And reflect what we see in the real world.

• Populations are divided into ‘trait groups’ or ‘…’ with varying … (in terms of cooperators and selfish individuals).
• Selection acts for or against … traits within groups
• Groups mix together before (this theory doesn’t require the strict … of groups that the “old” theories did)
• Because groups of cooperators are more successful than selfish individuals, they … more individuals to the mixed population
• They then split into new groups and there is another round of selection

Answer 43

demes, composition
cooperative,
isolation,
contribute

Question 44

The key in this formation of new groups is that…

Answer 44

individuals that share similar traits (in terms of cooperative/selfish behaviour) tend to group together.

• Because the cooperative groups were more successful the first time round, the second time round there are more cooperative groups. And again the cooperative groups are more successful and contribute more the next time the groups mix

Question 45

In these models, it can be shown that cooperative traits will spread through the population when …-… selection is stronger than …-… selection.

Answer 45

between-group, within-group

Question 46

3 general conclusions from “new” group selection models:

Cooperation is favoured by:

• increasing group …
• reducing individual …
• reducing …-group genetic variance, relative to …-group genetic variance (i.e. those with similar genotypes/phenotypes group together)

Answer 46

benefits (B),
cost (C),
within, between (r)

These new group selection models are therefore mathematically equivalent to Hamilton’s rule for the evolution of altruism: rB > C (argue opponents to new group selection models - no fundamental difference to inclusive fitness theory!)

Question 47

If new group selection and inclusive fitness models are mathematically equivalent, are they also equally useful?

Answer 47

NO! (argue proponents of inclusive fitness theory)

Inclusive fitness theory tells us that quantity which is maximised by natural selection under ALL conditions - this idea underpins all that we have talked about in this module. The theory has high generality.

New group selection models tell us when cooperation might evolve only under certain very narrow conditions. The theory has low generality.

Question 48

Empirical studies testing group-level selection:

One recent study on a species of social spider called Anelosimus studiosus (Pruitt and Goodnight, 2014) claims to support groups selection theory.

These spiders live in large groups, building … … for catching prey, which are…

Answer 48

communal webs, shared among members of the group

Question 49

In these groups, colony … is frequent (selection on groups could be high?), … is limited, and colonies have a mix of … and … phenotypes which are site-specific and affect reproductive success.

Answer 49

extinction, dispersal (so less genetic variation within groups than between groups), docile, aggressive

Question 50

In their experiment, Pruitt and Goodnight (2014) formed artificial colonies of varied mixes of docile and aggressive phenotypes, introducing them to different sites (“native” or “foreign” sites). They then monitored them after two generations, measuring the proportion of docile and aggressive individuals.

At each experimental site there was a naturally occurring mixture of aggressive and docile phenotype individuals. The experimental mixtures of phenotype were random with respect to the site. They monitored - after 2 generations - which of those colonies had survived at the different sites.

Found that…

Answer 50

At each of the two sites, the surviving colonies matched the pattern of colony size vs proportion of aggressive individuals seen at the sites naturally.

This was replicated at 6 different sites, and the same was found.

Pruitt and Goodnight argued that this is site-specific selection of a group-level trait.

Question 51

Colonies also adjusted their … to match that seen at the native site.

Answer 51

composition - suggests the group trait is locally adapted

Question 52

However, criticisms of this paper have included the fact that …-… selection was not investigated.

Successful groups are composed of successful individuals - individual level selection could be going on in these groups rather than group level selection per se.

Also, the … basis of these group traits is unknown. Aggression/docility assumed to be … determined - not yet been proven.

Answer 52

individual-level

genetic, genetically

• there’s been a lot of scepticism around this study
• also, Jonathan Pruitt is currently being investigated for scientific fraud due to inconsistencies, inaccuracies and duplications of data
• some of his papers have been retracted due to irrefutable errors

Question 53

There are a handful of other studies that have been cited by advocates of group-level selection to support their ideas, for example a study of … ants by Gordon et al. (2013).

They found that these ants adjust their level of … (a group-level trait) according to the availability of resources. It is suggested that a colony’s foraging behaviour may be … by … colonies, although this has not been proven.

However, these results are also entirely consistent with…

Answer 53

harvester

activity, inherited, daughter

individual level selection (as ants are composed of very closely related individual - hard to separate group from individual in these contexts)

Question 54

What do we conclude about multi-level selection theory?

Answer 54

• conditions for group selection (old or new) to operate are extremely limited in nature
• group selection models that work and inclusive fitness models are mathematically equivalent
• inclusive fitness theory is far more useful because it gives us the quantity that natural selection maximises and has very high generality
• Advocates of group selection often appear to have an agenda of denial - while their evidence should be evaluated fairly, advocates of group selection should do likewise