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
Has relative brain size increased in the hominids?
-yes
Was bipedalism the trigger for brain growth?
-The evolution of grassland - the plain - has been considered a driver of evolutionary change towards intelligence [ie freeing the forelimbs to allow hands to make tools etc.] -But, brain size has increased well after bipedalism: bipeds existed for two million, many several million, years before brains got bigger than chimp size. Freed hands wasn’t a trigger for cerebral expansion
Has the recent development of high culture been associated with any evolutionary change in the brain?
- hands develop before the big brain
- teeth= duration of childhood maybe the change in habilis and erectus
- all the stuff we think of as the result of big brain quite recent
What drove the growth of the brain in the hominids? (Variability Selection Hypothesis)
-Some say that rapid climate changes forced adaptation. Pulsing climate change; great lakes appearing and disappearing over 1000 years in the rift valley. The period of high climate variability (in Africa) lasted from about 2 Mya to 0.5 Mya. -The “Variability Selection Hypothesis” proposes that relatively rapid environmental change replaced habitat-specific adaptations and favored adaptations that increased the ability to respond and accommodate this change (such as increased intelligence and greater social complexity). Problem solvers survive.
When did our brain get bigger?
0.5 MY
What can you look for in the skull of an australophitecus?
-But australopithecine apes may have had longer childhoods. A theory says the lunate sulcus in chimps divides visual from other neocortex, and that “late afarensis” [australopithicus] endocasts show lunate sulcus positions suggestive of bigger proportion of non-visual cortex.
What is the role of the birth canal size in the brain size?
- birth canal size limits brain size
- there used to be more space, like chimps have more generous fit
- more of the brain growth occurs in humans after birth than in chimps
Does lot of brain growth in humans occur after birth?
-yes, especially in comparison with chimps
What is the significance of tooth development?
-tooth development is slow in modern humans, used to be faster in homo erectus -slower still in austrolophicitens -slow teeth= means must be nurtured for longer
What was the homo sapiens migration like?
-
What is the deal with Homo floriensis?
-flor.= look like erectus -really recent -13 000 years old -discovered in indonesia -tiny brain, short -maybe coexisted with Homo sapiens -possibly more interaction among the ancestors than we thought
What are the features of a bigger brain in our lineage and near relatives?
-
What is the difference/lack of in parcellation in humans and other animals?
-no difference in the regions, just the size
How does gene expression come into evolution of the brain?
- rather than genomic homology, patterns in gene expression might be more indicative of evolutionary changes in the brain v other organs
- gene expression pattern differ in the brain
- so maybe that is why
- the way the genome has been used to make the brain different, not big changes we could see
What is the pressure on brains to become bigger? (2)
1.benefits of social organisation 2.survival enhanced by being smarter (tools, clothes, hunting/gathering)
What are the high costs of the big brain? (4)
- Big brains need long gestation and long parental care= huge burden 2. Big head= difficult birth 3. Complexity: more genes, more mutations 4. Large energy expenditure/heat production
How do brains get bigger (2)?
- Faster growth? 2. Longer growth?
