Evolution of the NS Flashcards
What is the encephalization factor & what did it reveal?
how heavy is your brain compared to similar sized animals
found that human comes out on top
3 measures to determine how our brains have changed / differ
1) overall size –> birds, mammals, cartilaginous fish have increased relative brain size
2) relative region size increases - (esp neocortical scaling) –> most animals have the same core structures but diff sizes
3) brain architecture design (lamination, migration, segregation, mappings) –> esp neocortical paracellation
What does brain architecture design tell us about brain structure?
- bigger brains not necessarily more sophisticated
- human brain more dense than whale brain
- smaller brains are not always less
sophisticated as in a goldfish there are 15 different layers and interactions in the vagal lobe
WHAT HASN’T CHANGED: cortical thickness b/w brains where the 6 layered cerebral cortex has caught on with basic size and organization remaining relatively constant
Mammals have a bigger _____ than other animals
cerebral region
How are primate brains different?
- bigger brains relative to body size
- more neocortex
- more distinct architectures in neocortex
–> different levels of gyrification (amount of folding differs proportionally to amount of brain that is cerebral cortex)
What’s meant by parcellation? And what was found after parcellation of chimp and human brains?
Parcellation refers to dividing the brain into distinct regions or parcels, each with specific functional or structural properties. This process helps in studying the brain’s organization, connectivity, and function.
Parcellation shows that the basic design of subdivisions (esp in prefrontal cortex) are similar in humans and priamtes, same with language areas
What did variations in gene expresion suggest about human brain vs chimps?
Humans have greater PFC proportion and MORE variety of gene expression in PFC
More white matter and connectivity there
Compare humans with other hominins
- differences in body size, but bigger differences in brain size relative to body
- A afarensis = bigger brain body weight ratio
- H erectus = similar to us with an even larger ratio
Folding the cortical sheet allows more cortex in a smaller volume. Also, thinner
cortex allows. . . . . . . – is the number of layers and / or the thickness of the neocortical sheet, important for some reason?
tighter folding
Australopithecine -
Homo habilis -
Homo erectus -
2 million years (Africa)
2-1.5 mya (lineage to erectus?)
1.5 mya (found on 3 continents - but how recent was migration?)
What’s the problem with H. florensiensis?
Has a small brain but doesn’t fit on the same regression line as us - but in the intersection of the 2 lines (50,000 yrs ago)
What is the variable selection hypothesis?
rapi environmental change replaced habitat-specific adaptation & favoured those with ability to respond and accommodate change (i.e. higher intelligence = greater social complexity where problem solvers survive) –> migration hypothesis
What was NOT a cause of increased brain size?
evolution of grass lands
driver of intelligence (tool making, survival = to see = bipedalism)
§ But doesn’t make sense – brain size increased well after bipedalism (2mya) suggesting freed hands wasn’t a trigger for cerebral expansion (WATCH OUT)
Benefits of social organization
Forebrain, PF-region, survivability - cooperative, understanding communicating, strong social cohesion and complex social relationships (common cause) takes a lot of cognition - allows us to abstract, imagine, problem solving
What are some costs of having a big brain?
- need long gestation and parental care
- big head = harder birth
- complexity = more genes = more mutation
- large energy expenditure / heat production
What drove the evolution of big brains?
rapid climate changes forced adaptaion - variability selection hypothesis
The period of high climate
variability (in Africa) lasted from about 2 Mya to 0.5 Mya.
What are some features of a bigger brain?
o More cells, bigger cells? à in general no, only speculative
o Differentiation of cell types à don’t seem to have unique cells
o Connectivity (patterns, speed, dynamics) à Hard to measure, dont really know all, only
some retina (but similar to other animals)
o Molecular patterns dictating connectivity/plasticity à Plasticity fundamental for learning,,
developmental mechanisms however less clear
o Micro-architecture (lamination, migration, segregation, mapping) or parcellation?
What’s the assumed pattern of human evolution?
Ardipithecus
Australopithecus
Homo habilis
Homo erectus
Homo sapiens
Features of Australopithecus sediba
- Brain volume about 420 cc, similar to Australopithecus (and chimpanzee)
- Wider pelvis (but not driven by big-brained babies?)
- Maybe more frontal cortex
- only 2 mya, but small brain - is it an early hominin or a different lineage?
Are Australopithecines our ancestors?
Australopithecus sediba fossils have features of
Australopithicines and Homo (erectus) - this has added to debates about the
species’ place in the human lineage
Outline early hominin migration?
Conventionally it has been thought that
between 2 and less than a million
years ago, early Homo species spread
throughout East Africa and to Southern
Africa (Homo ergaster), but not yet to
West Africa. Around 1.8 million years
ago, Homo erectus migrated out of
Africa via the Levantine corridor and
Horn of Africa to Eurasia
More mixed features:
this 1.8 myo skull has features that look like H. habilis and H. erectus
