Lecture 25- Evolution and brains Flashcards
Do big or small animals have proportionally larger brain?
-small animals have proportionately larger brain -more of their bodyweight is devoted to the brain
What is the best way to measure brain size?
- a) total body weight
b) percentage body weight
c) encephalisation factor
What is the encephalisation factor?
- encephalization factor= if put all the vertebrates on a log scale= the factor is how far you deviate from that line
- we deviate by 0.69
How have brain changed in size in evolution?
- birds, mammals and cartilaginous fish have increased relative brain size
- separate only the mammals
- what pattern is it?
- birds fall into a similar pattern as cartilaginous fishes (sharks and rays) -mammals and birds seem to have the same relationship
How do brains differ in regional sizes in different animals?
- cerebral cortex increases in humans
- neocortical scaling mammals have more cerebral hemisphere
- regionally the difference is the amount of cerebral hemisphere
Do human and rat brain differ in the regions they have?
- no, still the same regions just different sizes
- all the bits we have other mammals have
- midbrain is remarkably similar
- same functions in the brainstem
- difference: in cerebral hemisphere(bigger in humans) and olfactory bulb (bigger in rats)
Are small brains simpler than large brains?
- similar structure in simple nervous systems as in complex
- just a miniature of the big brain
- complex incredibly small brain
- when in goldfish
Are bigger brains more sophisticated brains?
- the human= layers
- in whales= don’t seem to have as much stratification (the goldfish has the layers)
- big brain is more folded
What is the pattern of gyrification in primate brains?
- larger brains more folded
- bigger brain= more gyrification
- starts to fold on itself (like the insula cortex)
Has the cortical thickness change in brains?
- the cortical thickness does not change in brains
- not much
- relatively
Why hasn’t the cortical thickness changed?
- folding the cortical sheet allows more cortex in a smaller volume, also thinner cortex allows tighter folding
- as you increase the number of layers= have to have the connecting fibres
- as more cells= decrease density as have to accommodate more of the connecting fibres
What are the three things that are different in primate brains?
- bigger brains (in relation to body size) 2. more neocortex 3. more distinct architectures in the neocortex
What is the pattern with primate brains in terms of gyrification?
-larger brains= more gyrification
What are the three ancestors of Homo sapiens we look at the most? (hominids)
1.Australopithecine-Africa only, 2 million years 2. Homo habilis- 2-1.5 MYA- lineage to erectus? (only in Africa) 3. Homo erectus- 1.5 MYA found on three continents (Africa, Europe, Asia), but how recent was that migration?
What was the story about the newly discovered skull?
-the skull recently discovered= rewrote the history, has features only seen in separate species -small brain in homo habilis -large teeth- homo rudolfensis -long face= homo erectus -1.8 million years ol = suggests more interaction among our ancestors