Week 8: The human brain Flashcards
who has the largest brain
- sperm whale
- 10kg
relative brain size
large bodies require big brains
EQ
encephalization quotient
ratio of brain weight of animal to brain weight of “typical” animal of same body weight
modern human brain typical to primate
- no new cortical areas in human brains
- basic architectonic organization is the same
how can we measure a fossil brain size
- This is often done by creating an endocast, a cast of the inner surface of the skull, which then allows for volume measurement
- Alternatively, CT scans can be used to create digital endocasts and measure the volume directly
when did big brains evolve
between 800,000 and 200,000 years ago
original hypothesis of why hominins evolved big brains
darwin
No one doubts that the large size of the brain in man, relatively to his body, in comparison with that of the gorilla or orang, is closely connected
with his higher mental powers
why did hominins evolve big brains
social brain hypothesis
- primates evolved large brains to manage their unusually complex social systems
- in primates there is a quantitative relationship between brain size and social group size, presumably because the cognitive demands of sociality place a constraint on the number of individuals that can be maintained in a coherent group
why did hominins evolve big brains
dunbars number for humans
- 150
- the number of people you can have a relationship with involving trust and obligation
- with some personal history
why did hominins evolve big brains
theory of mind
the ability to understand another individuals mental state and take into account in ones own behaviour
expensive tissue hypothesis
- the brain and gut require large amounts of energy
- brain occupies 2% of body mass but 20% of bodies energy
- there is an evolutionary tradeoff between brain and gut size
what makes humans unique compared to closest relative
- bipedalism
- a larger and more complex brain
- the ability to use and create tools
- and the capacity for language and complex social structures
birth canal and brain size
- The size of the mother’s birth canal (the passageway through the hip bones) does limit the maximum size of a baby’s head at birth.
- This is a significant factor in the “obstetrical dilemma,” a challenge faced during human evolution where the need for larger brains conflicted with the constraints of the birth canal.
bipedalism and brain size
- The evolution of bipedalism and increased brain size in humans created a “dilemma” for the pelvis, as it had to be adapted for both efficient walking and the birth of larger-brained babies. This led to a compromise in the shape of the pelvis, with a narrower birth canal in women, potentially impacting the timing and ease of childbirth
brain development before birth
- midpoint of pregnancy at 15-20 weeks the number of brain cells in the cerebral cortex increase rapidly
- by the 7th month the fetus is emitting its own brain waves
altriciality
the state of being born or hatched in a helpless and immature condition, requiring extended parental care for survival
secondary altriciality
- Secondary altriciality describes the uniquely prolonged period of human infant dependency on parental care, a result of the brain’s immaturity at birth.
- While humans are born with some precocial features, their neurological immaturity leads to a longer period of reliance on care than in other primates.
- This dependency is considered secondary because it’s not the same as the “primitive” altriciality seen in many other mammals
precocial
hatched or born in an advanced state and able to feed itself and move independently almost immediately.
neuroplasticity
- refers to the brain’s ability to reorganize and adapt by forming new connections and strengthening existing ones in response to experiences and learning
- remodeled throughout life
