1. Fruit theory . Fruit are rich in vitamins, carbs, and calories so maybe big brains help us . keep track of fruit trees (not ripe all the time) by creating mental maps 2. Difficult food theory . Maybe big brains help us to figure out how to crack open nuts and shells, find and eat termites, etc. (to get nutritious food) 3. Social world theory . Maybe big brains help us to navigate a complex social world with many relationships, hierarchies, alliances, conflicts ... Usually called the Social brain hypothesis Testing the theories . Researchers looked at several variables within primates: . Neocortex ratio: Volume of neocortex (outermost layer of brain-responsible for perception & conscious thought) to rest of brain. This is a proxy for intelligence o Fruit in diet (to test fruit theory): No evidence for fruit theory o Extraction method (to test difficult food theory): No evidence for fruit theory o Group size (to test social world theory): Clear evidence for social world theory Humans weren't used in the original data set, but we can estimate where we would be: So it looks like ~150 people based on our neocortex ratio Group size . Data suggests people evolved in groups of 150 members Called Dunbar's number · Some evidence in support of Dunbar's number: o Subsistence societies (hunt, gather, agriculture) o Clan size average = 148.4 (pretty close to Dunbar's numberfl) o 150 is about how many living descendants (wives, husbands, children) a couple could produce after 4 generations o Hutterites divide society around 150 too hard to manage the society after that Average number of Facebook friends is 120ffi130 All of this supports Dunbar's number Language and group size . Language is like cheap social grooming : o It saves time & energy o It reduces the need for physical contact to maintain relationships o Language helps us to maintain relationships (and get bigger groups)
Do humans perform better socially? · One study compared children versus chimpanzees and orangutans . Did a physical problem solving task: Retrieve desired item with tool No real differencefl . Did a social problem solving task: Basically a social learning task Humans excelfl China video . showed cultural differences in: Language & Food Manners and etiquette . Vary around the world and seem arbitrary Greetings . Vary drastically around the world Handshake, Hug , Kiss, Bow Maori hongi . Traditional Maori greeting: Press noses together . The greeting has symbolism and meaning: Sharing the breath of life & Welcoming someone · Superficially similar to Inuit kunit (Eskimo kiss) · Inhale while pressing nose, often press nose on cheek, Done between lovedffiones Cultural differences . Often appear arbitrary & change with time Where does culture come from? Are cultural differences genetic? · Genetic differences exist between human groups Most obvious is skin colour · Maybe cultural differences are genetic too? Are cultural differences genetic? . Human groups are genetically similar: Rapid expansion of human populations means more genetically similar than many other