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why is absolute brain weight not informative?

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


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


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.


what would encephalisation include?

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


talk about mammal/ primateenc/human encephalisation

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.


what are costs of having bigger brains

• Altriciality - birthing through birth canal
• Energetic costs


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

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

thus babies are born very vulnerable


how much energy does the brain take up?

o Human brains take about 25% of daily energy intake


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

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.


what do the significant costs of big brains mean?

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


what have been the arguments for bigger brain size?

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


what can the arguments for brain size be broken into

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


which arguments can be put into selection based upon nutrition?

tool use and energetic benefits, and spatial memory


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

Machiavellian intelligence (deception) and group size


what humans showed use of tools?

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


evidence for butchering/ tools for killing?

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


what is the major issue with the tool use hypothesis?

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


give e.g.'s of animals using tools

• 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.


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

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

that slightly bigger brains may be needed for tool use


overall what can we say about the tool use hypothesis?

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.


what is the spatial cognition hypothesis?

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.


what is the issue with spatial cognition hypothesis

non-human species can do this also

scrub jays and mangabey monkeys


bird e.g. of spatial cognition

• 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.


monkey e.g. of spatial cognition

• 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.


what can be said about human spatial cognition

• 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.


overall what can be said about the spatial cognition hypothesis?

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.


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

• 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.


what is the issues with Machiavellian hypothesis?

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.


e.g. of manipulation and deception in apes

• 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.


rank and understanding of social status in chimps

• 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.


TOM in chimps evidence

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