9. Evolution of the brain

Question 1

why is absolute brain weight not informative?

Answer 1

Dolphins, wales elephants e.g. all have bigger brains than humans but allometric scaling as the body gets bigger the brain must too get bigger so absolute brain size is not very informative

Question 2

what is it called when brain size is relevant to the rest of the body?

Answer 2

Encephalisation

o Ratio of brain weight to brain weight of “typical” animal of the same body weight (Jerison, 1973). Taking how much brain that needs to operate just for a body to operate and seeing how much is left for other things.

Question 3

what would encephalisation include?

Answer 3

• Total Brain Mass= Brain for body size + residual for higher functions.

Question 4

talk about mammal/ primateenc/human encephalisation

Answer 4

Mammals have become bigger brained- especially primates. Reptiles have not got bigger brains. Mammals are more encephalised than would be expected compared to other species and primates especially and apes are more encephalised other primates.
If we look at hominids, then there is an extremely steep slope of our ancestors becoming rapidly more encephalised.

Question 5

what are costs of having bigger brains

Answer 5

• Altriciality - birthing through birth canal

* Energetic costs

Question 6

based on development when would we predict human babies to be born? what are the effects of this?

Answer 6

21 rather than 9 months but energetic costs to mother would be too big

thus babies are born very vulnerable

Question 7

how much energy does the brain take up?

Answer 7

o Human brains take about 25% of daily energy intake

Question 8

what are their clear changes in lineage to support us having big brains?

Answer 8

o Clear changes in the way we have eaten in lineage in order to support these brains e.g. roots/ large mammals and cooking food because less energy breaking down the food. These directly support our capacity to grow big brains.

Question 9

what do the significant costs of big brains mean?

Answer 9

• Because all of these costs there must be a hugely beneficial reason for us having big brains.

Question 10

what have been the arguments for bigger brain size?

Answer 10

• tool use and energetic benefits
• spatial memory
• Machiavellian intelligence
• group size
• sexual selection

Question 11

what can the arguments for brain size be broken into

Answer 11

• selection based on nutrition
• selection based on social cognition and advantage
• selection based on group size
• sexual selection

Question 12

which arguments can be put into selection based upon nutrition?

Answer 12

tool use and energetic benefits, and spatial memory

Question 13

which arguments can be put into selection based upon social cognition and advantage?

Answer 13

Machiavellian intelligence (deception) and group size

Question 14

what humans showed use of tools?

Answer 14

• Flint tools seen from homo habilis onwards- making these tools takes practice and need to be good at it.

Question 15

evidence for butchering/ tools for killing?

Answer 15

• Early homo species Animal based food 65% gathered plant foods 35% Cordain et al., 2002

Question 16

what is the major issue with the tool use hypothesis?

Answer 16

there are use of tools in non-human species- thus clearly don’t need brains as big as ours to use tools

Question 17

give e.g.’s of animals using tools

Answer 17

• Termite fishing by bonobos- use thin sticks to get termites have to be thin and straight and also stripped down so just like flint tools they have to prepare the tools and it is deliberate.
• Nut Cracking by chimps- hit nuts against stones. Can scatter good nut cracking stones around chimps routes and they will remember where they are and come back for them. Uses strategic planning for tools.
• Crows using sticks for larvae fishing.
• Capuchins- engage in nut cracking (bubble trap task where capuchin must push out a treat without letting it fall into a trap) shows strategic planning and basic understanding of basic spatial relationship.
• Crocodiles putting sticks on themselves to look like a log.

Question 18

what is strange about animals that use tools and what does this suggest?

Answer 18

• All of these species have pretty big brains compared to their broader taxonomic groupings.

that slightly bigger brains may be needed for tool use

Question 19

overall what can we say about the tool use hypothesis?

Answer 19

Is probably learnt in a more basic way rather than having theory of mind and deception. Can use tools without having all the higher mental functions that we associate with tool use in humans. So to say that tool use is what drove brain expansion is weak because none of these species have brains like ours.

Question 20

what is the spatial cognition hypothesis?

Answer 20

Good spatial and temporal cognition means you can think more about storage of food and engage in more spatially based task which again could be advantageous to supporting nutrition.

Question 21

what is the issue with spatial cognition hypothesis

Answer 21

non-human species can do this also

scrub jays and mangabey monkeys

Question 22

bird e.g. of spatial cognition

Answer 22

• Scrub jays food cache–Clayton
• Cache species means They will get food and store it and come back for it later
• Ice cube tray of sawdust with Duplo building blocks in front of it. Scrub jay will bury food in slot in tray. Can take scrub jay out for number of moths and coming back to it will remember the right slot they stored food in based upon the Duplo blocks in front of them as a reference.

Question 23

monkey e.g. of spatial cognition

Answer 23

• Memory for in-season fruit trees in Mangabeys (monkeys) Janmaat et al., 2006
• If we know that there is a tree 1) that is in season in April and another tree that not in season and then follow the Mangabeys, and ask how many times they changed direction- the more they change direction the more random their finding is of in-season trees. They don’t show many random changes in direction indeed instead their paths seem relatively straight to the fruiting trees.

Question 24

what can be said about human spatial cognition

Answer 24

• To a certain degree we may as humans be far worse than monkeys and chimps, we are not super accurate at this we just think we are because of maps.

Question 25

overall what can be said about the spatial cognition hypothesis?

Answer 25

Can’t mean then that spatial awareness is what gives us our large brains. There’s nothing in spatial memory that we have that that other species do not.

Question 26

who argued machiavellian intelligence for brain size and what did they argue

Answer 26

• Byrne & Whiten (1988); Whiten & Byrne (1997) argue that manipulative devious behavior is what has driven human brain evolution (and primate) the capacity to strategically deceive and manipulate our social relationships.

Question 27

what is the issues with Machiavellian hypothesis?

Answer 27

again some chimps and monkeys seem to have this TOM and ability to manipulate- so if they are capable then doesn’t explain why human brains need be so much larger because we’re all social species.

Also, if group living promotes Machiavellian intelligence then we would expect to see this in all social species and we do not.

Question 28

e.g. of manipulation and deception in apes

Answer 28

• Byrne & Whiten (1988) Hamadryas Baboons- female observed grooming a male who was not her mate behind a male. Her male mate could see her but not the other male- she was doing this knowing that her mate did not know what she was doing and must have had some idea of what her mate could see. They argued that being able to make these manipulative and deceptive decisions is highly advantageous in navigating the social environment that you live in and getting the best out of social relationships.

Question 29

rank and understanding of social status in chimps

Answer 29

• Silk (1999)- Bonnet macaques and other’s rank – can play the sound of a dominant individual attacking a subordinate individual and the subordinate giving way and vice versa, or can play the sound of a dominant individual attacking a subordinate. When two individuals are not around these sounds can be played. If play the first the macaques are not interested it is a sound that they are used to but if subordinate is attacking and dominant is going on then all monkeys have heads up of surprise and alertness as they know this shouldn’t happen and it is relational information that is new.

Question 30

TOM in chimps evidence

Answer 30

Hare et al. 2000
o Subordinate and dominant chimps initially in separate cages and hatches where they can see through to the central cage.
o Two occluders and a piece of food is placed behind one of the occluders with either both chimps looking and then either left or dominants hatch blocked and food is moved. So in one scenario the dominant knows where the food is and in the other the subordinate (if TOM) knows that the dominant chimp has a false belief.
o So test is to see if the chimps rush forward to the food- if both rush for same food subordinate will get attacked.
o If subordinate knows dominant has false belief they are more likely to rush in to get the food.
o May not be complete TOM but they can know what others do and do not know.
o Children can pass competitive tasks at an earlier age than they can pass more complex TOM tasks.

Krupenye et al., 2016
o Eye tracking when watching false belief scenarios
o Suggests that there is clear evidence that some individuals amongst other great ape species are able to correctly focus their attention in a false belief paradigm

Question 31

what happens to social relationships as group size increases?

Answer 31

• Social relationships increase dramatically with group size.  three in a group then three relationships to keep track of 4=6, 5=10 and by the time you reach 6 group members there is 15 relations to keep track 10=44.
• If you plot that as the group gets bigger the number of relationships increases nearly exponentially.

Question 32

what brain area specifically has been focused on and by who in regard to group size?

Answer 32

Dunbar, has focused very much on the idea that the Neocortex has evolved as a way of providing additional brain capacity to track a large number of social relationships in a close networked living species.

Question 33

what is the Neocortex responsible for?

Answer 33

o Intelligence, sensory information, planning behaviour (speech), social manipulations, tactical deception.

Question 34

talk about the neocortex ratio

Answer 34

• Neocortex ratio= Neocortex volume/ brain volume (how much is cortex versus other stuff)
• Neocortex ration positively correlated with larger group size in primates (e.g. Kudo & Dunbar, 2001) the bigger the group size the larger the neocortex ratio.
• There is not a huge number of data points in their research but there is a broadly positive relationship.

Question 35

who suggested social intelligence hypothesis and what did they suggest

Answer 35

(related to group size)

• Dunbar (1998)
Human intelligence did not evolve Primarily as a means to solve ecological problems, but rather as a means of surviving and reproducing in large and complex social groups.

Need TOM to form good relationship and engage in altruism/deception/ coalition formation

Evidence to suggest that groups of 150 are particularly successful.

When hominids Started living in large groups, selection favoured greater intelligence/ social skills. in a group where everyone is interdependent on everyone else for their success being able to navigate that group is really important for reproductive success.

• Brain creates a Cognitive constraint -Even if environment could support more it is constrained by cognition.

Question 36

what has the human predicted group size been placed at based on our neocortex size?

Answer 36

For humans has been argued that the predicted max group size is about 150.

Big brains able to support big groups.

Question 37

evidence on human group size

Answer 37

Dunbar (2008)

most human formed groups to tend to be around/ definitely below this 150 mark for example

Chistmas card networks= 154
hunter gatherer communities= 148
doomsday book villages= 150

amongst many others

Question 38

what is important to note as you add more people to a group?

Answer 38

The more people that there are the more that you have to think about not just what you think about them but what they think about each other and how many layers of that you really need to understand what is going on in your social group.

Question 39

what did Dunbar argue about TOM?

Answer 39

there is a limit on our intentionality and how much we can understand TOM.
• First order mental state=I think something
• Second order= basic TOM ‘I think that you think’
• Third level intentionality= ‘You think that I think, that you think’

and so on- humans seem to struggle to do this past the fifth level in a TOM task

Question 40

what has been found about those who perform better on a TOM task?

Answer 40

Stiller & Dunbar (2007); Powell et al., (2010)- People who can perform better on these intentionality tasks then have larger support cliques. The more people you are able to keep supportive close relationships with. These groups are very important because these are people supporting you in social environment. Can draw on these and potentially maximise reproductive potential.

Question 41

what still needs explaining in terms of social intelligence hypothesis? And what ideas were put forward to explain this?

Answer 41

Why is there selection for these big groups for humans?

• Predation…?- one of Dunbar’s arguments- it is always better to be a bigger group because decreases risk of predation if you are one of these species who is able to have these big groups then you will have a large advantage.
• Inter-group competition…?- favours bigger groups, if you’re the bigger group you are better able to compete with other members of your species. Would favour individuals who are able to maintain these strong cognitive defences against group living to be a strongly cooperative species who live together.

Question 42

what is the issue with just using the neocortex?

Answer 42

However, it has been argued that all this focus on what’s going on with the neocortex is missing out on some of the other important things about brain size across species.

Question 43

who argued against using neocortex and what did they find?

Answer 43

Barton (2012)

• A lot of the increase in size in the neocortex is white matter (axons/ connective tissue) the cerebellum increases more in grey matter than the neocortex- so more cell bodies.
• This is very important because if we remember allometric scaling about size of body and brain- so if all you have is a lot of extra white matter- it tells you that there is more connections but maybe more long range connections- could be about the axons having to go further rather than there being more axons to start with. A lot of the increase in the neocortex might just be axons traveling further and this isn’t actually increasing reasoning/ learning ability it is just a physical increase in the size needed to travel. Whereas the cerebellum is increasing a lot in grey matter which is more cells and more processing power and therefore is quite important.

Question 44

what other brain area has been proposed in social brain hypothesis?

Answer 44

Cerebellum (Barton, 2012)

Question 45

what did Barton find about the cerebellum?

Answer 45

• Cerebellum increases at least as much as the neocortex

• Burton 2012- “neocortex size correlates significantly with social group size…but not extractive foraging, whereas cerebellum size correlates significantly with extractive foraging but not social group size.
• So potentially neocortex might be linking into these social relationship and the cerebellum is doing something too in motor sequence planning and tool use and getting more nutrition from environment.

Question 46

what have key functions of the cerebellum been suggested to be?

Answer 46

o Motor coordination
o Sequence processing
o Planning thereof?
o (Including language? Can think about planning words and syntax)

Question 47

what did Dunbar suggest in terms of group size?

Answer 47

Dunbar (1992) suggested that there was a species specific upper limit to group size that is set by purely cognitive constraints: animals cannot maintain the cohesion and integrity of groups larger than a size fixed by the information-processing capacity of their neocortex.  the group size identified by this relationship appears to depend on the maximum number of individuals with whom an animal can maintain social relationships by personal contact

Question 48

what is social grooming in primate groups used for?

Answer 48

It is generally accepted that the cohesion of primate groups is maintained through time by social grooming (see Dunbar 1988). Social grooming is used both to establish and to service those friendships and coalitions that give primate groups their unique structure

Question 49

what correlates with social grooming

Answer 49

As might be anticipated, the amount of time devoted to social grooming correlates well with group size, notably among the catarrhine primates (Old World monkeys and apes; Dunbar 1991).

Question 50

why does a larger group mean greater grooming time?

Answer 50

Effectiveness of a coalition is directly related to the amount of time its members spend grooming each other (Dunbar, 1984)- thus larger group the more grooming time.

Question 51

what two bits of evidence would we need to have to support group size and social brain hypothesis?

Answer 51

What brain size would we predict for anatomically modern humans, given our current neocortical size? I then ask whether there are any observed human group sizes that correspond to this predicted value

Question 52

what does Dunbar argue for cases where ‘supposed’ human group size is not seen?

Answer 52

• Dunbar argues that in cases where this is not seen e.g. Australian Aboriginal tribes living in the central desert regions lack the larger clanlike groups does not necessarily refute the hypothesis. The marginal habitats occupied by these peoples seem to dictate a foraging strategy based on small, dispersed groups living in very large territories; this almost certainly creates communication problems that preclude the formation of larger social networks

Question 53

archaeological records hunting and brain size

Answer 53

Wynn 1988- pointed out that the evolution of large brain size within the hominid lineage does not correlate well with the archaeological record for changes in tool construction. The markedly improved tool designs of the Upper Palaeolithic can thus be better interpreted as a consequence rather than a cause of enlarged brain size

Question 54

what is Dunbar’s overall suggestion on social brain

Answer 54

Suggestion is that evolution of this increased capacity arose out of the need to coordinate the large number of interpersonal relationships necessary to maintain the cohesion and stability of larger than normal groups.

There is a cognitive limit to the number of individuals with whom any one person can maintain stable relationships, that this limit is a direct function of relative neocortical size

Question 55

link social brain theory to language development

Answer 55

. argued that the need to increase group size at some point during the course of human evolution precipitated the evolution of language because a more efficient process was required for servicing these relationships than was possible with the conventional nonhuman primate bonding mechanism (i.e., social grooming).

Question 56

what evidence has been found against the social brain hypothesis?

Answer 56

DeCasien et al., 2017- Primate brain size is predicted by diet but not sociality

Question 57

what would social brain hypothesize about brain size in polyandrous and monogamous primate species

Answer 57

social brain hypothesis would stipulate that polyandrous primate species would have the largest brains as this would be consistent with the idea that systems that promote the most interactions and relationships between the greatest numbers of individuals might be the most cognitively demanding.

Question 58

findings on polyandrous and monogamous brain size

Answer 58

Some studies have supported this (Clutton-Brock, & Harvey, 1980; Shultz, & Dunbar, 2007)

BUT others have found the opposite that monogamous species have the largest brains (Schillaci, 2006)- researchers finding these have argued that these species have larger brains because monogamy require greater deception and manipulation abilities for obtaining extra-pair copulations or require conflict resolution and coordination abilities for bond maintenance.

Question 59

issues with many studies that have been on primate brain size evolution in support for social brain hypothesis

Answer 59

DeCasien et al., 2017 argue that

within these studies of primate brain size evolution, species sample sizes used in analyses have been small and idiosyncratic

older studies used weak statistical analysis techniques.

Many include phylogeny that has become outdated.

Question 60

issues of using group size

Answer 60

DeCasien et al., 2017 argue that

Difficulties associated with assigning appropriate proxies of social complexity and cognitive complexity should not be underestimated. For example, mean group size is, ‘at best, a crude proxy’ of social complexity, because larger groups may not be characterized by a corresponding increase in the number of differentiated relationships/interactions. Future studies using more sophisticated proxies may provide better support for the social brain hypothesis.

Question 61

neocortex and social brain hypothesis issues

Answer 61

DeCasien et al., 2017 argue that there is too much of a focus on the neocortex rather than just brain size- Social brain hypothesis stipulates that it is total brain size not just neocortex size- Dunbar 1993- only uses neocortex The subsequent focus on the neocortex was not always based on a priori reasoning, but because neocortex analyses sometimes showed the strongest correlations with the social variables under examination. Regions outside the neocortex are also involved in complex cognitive functions (for example, cerebellum, hippocampus, striatum and studies show that overall brain size predicts global cognitive ability across non-human primates

Question 62

pros with the methods used by DeCasien et al., 2017

Answer 62

Used a much larger and more representative sample of primates (>140 spp., more than tripling the sample size of previous studies) and tested whether multiple measures of sociality (mean group size, social and mating system separately) explain variation in brain size after controlling for body size, diet and phylogenetic history.

Question 63

what did DeCasien et al., 2017 find?

Answer 63

Contrary to the predictions of the social brain hypothesis, our results indicate that none of the sociality measures examined here explain relative brain size variation in primates, which is predicted only by diet, with frugivores having relatively larger brains than folivores.

Question 64

what do DeCasien et al., 2017 conclude about frugivory and brain size

Answer 64

Together, it seems that frugivory not only provides selective pressures on cognitive processing3–5, but compensates for the costs of a metabolically expensive brain via facilitating higher energy turnover and/or lower energy allocation to digestion.

Question 65

issues suggested (not by deCasien) about social brain hypothesis

Answer 65

1) complex social behaviors thought unique to humans have been found in other taxa that don’t exhibit huge brains
2) social brain hypothesis assumes that complex social environments are more cognitively demanding than physical but no evidence for this
3) rapid expansion of hominoid cerebellum indicates that technical intelligence is equally important as social.

Question 66

talk about complex social behaviors being found in other taxa

Answer 66

complex social behaviours (for example, coalitions, reciprocation) that were previously assumed to be unique to primates have now been found in other taxa that do not exhibit relatively large brains compared to other members of their order (such as spotted hyenas- Holekamp et al., 2004).

Therefore, the premise that social complexity necessarily requires cognitive complexity may not always hold, as social living challenges might not require flexible cognitive solutions in real-time, but could be solved using simpler evolved rulesof-thumb

Question 67

talk about cognitive demands of physical and social environments

Answer 67

the hypothesis that complex social environments are more cognitively demanding than properties of the physical environment is partially derived from the idea that the former is more unstable than the latter and requires more processing power to navigate. This has not been demonstrated quantitatively (Bshary et al., 2011)

Question 68

talk about cerebellum and social brain hypothesis

Answer 68

• Rapid expansion of the hominoid cerebellum suggests technical intelligence was at least as important as social intelligence in human cognitive evolution (Barton & Venditti, 2014)
• Technical innovations also allowed for the increased incorporation of meat in the diet, and the advent of cooking meat and other foods

Question 69

what overall does DeCasien et al.’s study suggest?

Answer 69

Together with the present study, this body of comparative work suggests that both human and non-human primate brain evolution was primarily driven by selection on increased foraging efficiency, with associated changes then perhaps providing the scaffolding for subsequent development of social skills

Question 70

how much bigger are human brains than our body size predicts

Answer 70

• Human brains are 6x larger than would be expected for their body size compared to the average primate, while primates as a group have sig larger brains than would be expected for mammals of the same size.

Question 71

what criticisms still remain about brain studies

Answer 71

mosaic brain - size is not enough it should be more about structure

Question 72

why has it been argued that brains size is used

Answer 72

As Bouchard (2014) points out- size dominates the literature not simply because it is important in its own right, but because it is easy to measure both in live organisms and in endocasts

Question 73

what has been hypothesized to also be important as well as brain size

Answer 73

Even investigators who have focused on the correlation between brain size, cortical convolutions and cortical thickness make it clear that they believe these measures are only relevant because they reflect the structural integrity of these regions and they hypothesize that other micro-anatomical characteristics as well a neuronal circuitry will prove to be important (Luders et al. 2007)

Question 74

what is evidence that there is more importance than just brain size

Answer 74

This prediction has proven to be true as Jolles et al. (2011) have recently shown that functional connectivity differences between brain regions cannot be explained by gray matter density alone.

Question 75

what does future research into human brains need to do?

Answer 75

Future research must focus in incorporating these findings into research to fully understand what makes the human brain different.