9. Evolution of the brain Flashcards Preview

human evolution > 9. Evolution of the brain > Flashcards

Flashcards in 9. Evolution of the brain Deck (75)
Loading flashcards...
1
Q

why is absolute brain weight not informative?

A

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

2
Q

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

A

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.

3
Q

what would encephalisation include?

A

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

4
Q

talk about mammal/ primateenc/human encephalisation

A

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.

5
Q

what are costs of having bigger brains

A
  • Altriciality - birthing through birth canal

* Energetic costs

6
Q

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

A

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

thus babies are born very vulnerable

7
Q

how much energy does the brain take up?

A

o Human brains take about 25% of daily energy intake

8
Q

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

A

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.

9
Q

what do the significant costs of big brains mean?

A

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

10
Q

what have been the arguments for bigger brain size?

A
  • tool use and energetic benefits
  • spatial memory
  • Machiavellian intelligence
  • group size
  • sexual selection
11
Q

what can the arguments for brain size be broken into

A
  • selection based on nutrition
  • selection based on social cognition and advantage
  • selection based on group size
  • sexual selection
12
Q

which arguments can be put into selection based upon nutrition?

A

tool use and energetic benefits, and spatial memory

13
Q

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

A

Machiavellian intelligence (deception) and group size

14
Q

what humans showed use of tools?

A

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

15
Q

evidence for butchering/ tools for killing?

A

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

16
Q

what is the major issue with the tool use hypothesis?

A

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

17
Q

give e.g.’s of animals using tools

A
  • 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.
18
Q

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

A

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

that slightly bigger brains may be needed for tool use

19
Q

overall what can we say about the tool use hypothesis?

A

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.

20
Q

what is the spatial cognition hypothesis?

A

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.

21
Q

what is the issue with spatial cognition hypothesis

A

non-human species can do this also

scrub jays and mangabey monkeys

22
Q

bird e.g. of spatial cognition

A
  • 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.
23
Q

monkey e.g. of spatial cognition

A
  • 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.
24
Q

what can be said about human spatial cognition

A

• 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.

25
Q

overall what can be said about the spatial cognition hypothesis?

A

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.

26
Q

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

A

• 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.

27
Q

what is the issues with Machiavellian hypothesis?

A

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.

28
Q

e.g. of manipulation and deception in apes

A

• 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.

29
Q

rank and understanding of social status in chimps

A

• 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.

30
Q

TOM in chimps evidence

A

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

31
Q

what happens to social relationships as group size increases?

A
  • 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.
32
Q

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

A

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.

33
Q

what is the Neocortex responsible for?

A

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

34
Q

talk about the neocortex ratio

A
  • 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.
35
Q

who suggested social intelligence hypothesis and what did they suggest

A

(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.

36
Q

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

A

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

Big brains able to support big groups.

37
Q

evidence on human group size

A

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

38
Q

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

A

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.

39
Q

what did Dunbar argue about TOM?

A

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

40
Q

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

A

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.

41
Q

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

A

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.
42
Q

what is the issue with just using the neocortex?

A

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.

43
Q

who argued against using neocortex and what did they find?

A

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.
44
Q

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

A

Cerebellum (Barton, 2012)

45
Q

what did Barton find about the cerebellum?

A

• 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.
46
Q

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

A

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

47
Q

what did Dunbar suggest in terms of group size?

A

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

48
Q

what is social grooming in primate groups used for?

A

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

49
Q

what correlates with social grooming

A

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).

50
Q

why does a larger group mean greater grooming time?

A

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.

51
Q

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

A

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

52
Q

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

A
  • 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
53
Q

archaeological records hunting and brain size

A

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

54
Q

what is Dunbar’s overall suggestion on social brain

A

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

55
Q

link social brain theory to language development

A

. 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).

56
Q

what evidence has been found against the social brain hypothesis?

A

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

57
Q

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

A

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.

58
Q

findings on polyandrous and monogamous brain size

A

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.

59
Q

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

A

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.

60
Q

issues of using group size

A

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.

61
Q

neocortex and social brain hypothesis issues

A

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

62
Q

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

A

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.

63
Q

what did DeCasien et al., 2017 find?

A

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.

64
Q

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

A

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.

65
Q

issues suggested (not by deCasien) about social brain hypothesis

A

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.

66
Q

talk about complex social behaviors being found in other taxa

A

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

67
Q

talk about cognitive demands of physical and social environments

A

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)

68
Q

talk about cerebellum and social brain hypothesis

A
  • 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
69
Q

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

A

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

70
Q

how much bigger are human brains than our body size predicts

A

• 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.

71
Q

what criticisms still remain about brain studies

A

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

72
Q

why has it been argued that brains size is used

A

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

73
Q

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

A

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)

74
Q

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

A

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.

75
Q

what does future research into human brains need to do?

A

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