Principles of Neuroscience Lecture 24 Brain Evolution Flashcards
What are the three ways we can compare brain size? Which is the most useful?
Size of brain
Brain to body weight ratio
Encephalisation factor - the most useful. This tells us how far off the average for the species’ size its brain is
What did Cuvier say about brain size?
All else being equal, smaller animals have a greater body to brain weight ratio
What is special about cartilaginous fish?
These have a very steep slope for the graph of brain vs. body weight
Describe differential regional size in the brain of different animals
In vertebrates, the relative sizes of different regions in the brain varies
Eg. Humans have, most importantly, a very large neocortex, whilst other animals have an olfactory lobe that is bigger than ours
What is meant by “a rat is a monkey is a human”?
This is saying that all these animals have the same functional regions in the brain, which are also organised in a similar way, they are just different sizes
Which area of the brain is fairly unique to higher animals?
Neocortex
How does brain architecture in simple, as well as very large animals, compare with human?
Not vastly different, as we might expect
Goldfish: everything that is present in humans is here, it is just more dense and miniature
Whale: lack the lamination that we see in humans
Describe differences in gyrification in different monkeys
As brain size and complexity increases, there is an increase in gyrification
Describe differences of cortical thickness in different monkeys
As the brain size and complexity increases, there is no increase in the thickness of the cortical layer
What is special about hominids?
They have a very large brain, with a very large neocortex
What are the three different trajectories of brain vs. body weight?
Monkeys: not a steep slope
Australopithecines: also, they did not show a huge expansion in brain size over the years
Hominids: huge increase in brain size over the years
Why is a big brain better?
More cells
Better connectivity
Greater differentiation of cell types
Different cytoarchitecture
Describe migration of hominids
Out of Africa to Middle East, then Europe and Asia
What is interesting about Homo Florensis?
Despite being alive not that long ago, they had a tiny brain
On which trajectory is Homo Florensis? (Body vs. brain weight?)
It is ambiguous, we can’t tell whether it is a hominid or an Australopithecine
Why are big brains associated with higher function?
.
Describe how we can look at evolutionary changes in terms of epigenetic effects
Monkeys and humans appear to be quite related when we look solely at the genetic material
However, it is more useful to look at the expression of these genes. This shows us to be not so closely related
What were the evolutionary pressures for an expansion of brain size?
- Social interaction is selected for, which is a feature of a bigger brain
- Better survival for those with a big brain
What are the costs of having a larger brain?
- Long gestation period, and babies are helpless for a long time: thus, it’s a burden on the mother
- With a bigger brain, there is more chance of mutation or damage
- Birth becomes very difficult, because the birth canal is barely wide enough for the brain
What does comparison of parcellation in macaques and humans indicate?
If we look at the Brodmann’s areas in macaques and humans, we see there is much Homology.
The structure of the brain is very similar, there is not one thing that humans have that monkeys do not
How did human brains expand?
What mechanisms are there for brain growth?
They don’t grow at a faster rate, they just grow for longer
Describe how sexual pressures may select for a bigger brain
Bower bird: collect and sort materials for the nest to attract females for mating
A big brain is required for such behaviour.
Thus a bigger brain is selected for
In humans, we could compare this to humour, wit, cleverness etc. those with these traits may have had a larger brain, and these individuals were more likely to mate
What is the mechanism for growing a larger brain?
Over expression of beta catering will cause rats to grow a bigger brain
