Chapter 6

Question 1

evolutionary similarities between humans and all other organisms

Answer 1

• DNA: have both coding and non-coding regions
• genes: function = produce protein in coding region of DNA
• cells: same structure, even from protozoa (single cell) to humans
• tissues: species-specific structure only develops with growth (embryo state = the same across species; e.g. wing/hand/fin)
• brain structures: same parts (cerebrum, cerebellum, optic tectum, olfactory bulb), just different sizes/organizations
• behavior: collaborative mechanism

Question 2

behavior and brain circuitry

Answer 2

• simple: feeding, moving, mating
• complex: learning/memory
• cognition: empathy, morality

Question 3

natural selection

Answer 3

theory that says evolution proceeds by differential success in reproduction
- example: evolution of behavior:
+ members of pop. often vary greatly in behavior traits
+ behavior traits = inherited from parents
+ all species are capable of producing more offsprings than envi. can support
+ lack of food + resources -> many offspring don’t survive
=> individuals who inherited behavior traits have a higher probability of surviving and reproducing in a given envi. + tend to leave more offsprings than others
- can apply to evolution of brain size (cortical area) -> better at problem-solving

Question 4

phylogeny

Answer 4

study of the evolutionary history and relationships among individuals or groups of organisms (‘family tree’)

• example: humans are most closely related to bonobos
• differences between individual humans = 0.1%, between humans and chimps/bonobos: 1.2%

Question 5

evolutionary adaptation of brain

Answer 5

• all vertebrate brains share the same basic structures but different nervous systems (nerve nets, radial nerves, neural rings, simple ganglia, central + peripheral systems, etc.)
• all mammals have the same main brain structure because of common ancestor
  + size, proportions, and locations of structures are subjected to evolutionary modification
  + forebrain size correlates positively with ability to cope with envi. challenges
  + lifestyles influence cortical organization:
  + nocturnal rodents (e.g. rats) use whiskers -> large part of cortex devoted to whiskers
  + diurnal rodents (e.g. squirrels) have large part for vision
  + platypus uses bill to detect mechanical + electrical stimuli -> cortex is devoted to bill
• if a specific behavioral trait = controlled by specialized brain nucleus -> more advanced trait -> larger nucleus

Question 6

food caching

Answer 6

• common in corvidae (crows, jays) ad paridae (tits, chickadees)
• function: survive in the winter
• Clark’s nutcracker:
  + caches ~98,000 seeds per season
  + remarkable long-term spatial memory: can relocate seeds 9 months later and even when then they’re buried under 3ft of snow
• strong correlation between food caching and forebrain hippocampus size
  + more food-storing behavior (wild vs. captive bird, northern vs. southern bird), greater hippocampal volume

Question 7

hippocampus and human behavior

Answer 7

• encodes learning (short to long term)
  + e.g. mental maps for directions -> taxi drivers in London, where the streets are very complicated, have a larger hippocampus than other people; part of it grew as they spend more time on the job

Question 8

birdsong and brain nucleus

Answer 8

• songbirds have a specialized “song circuit” for learned song production; non-vocal learning birds do not
  + males sing -> males have a more developed circuit compared to females
• song repertoires evolve to attract females -> strong correlation between song repertoire size and forebrain song nucleus HVC (human equivalent: Broca’s area) => evolved from sexual pressure

Question 9

evolution of brain size

Answer 9

• difference between classes of vertebrates: brain size and elaboration
  + all mammals: 6-layered cortex
  + reptiles: first to have cerebral cortex, but only 3 layers
• brain weight relative to body size varies between + within classes, but rela is similar for all vertebrates
• encephalization factor: measure of brain size relative to body size (brain weight/body weight)
  + elephant: 0.19, human: 0.71
• primates: brain regions that develop later -> more enlarged
  + achieved by prolonging later stages of development
  + overall size increases -> sizes of different parts increase at different rates (cortex’s rate = similar to total size, cerebellum stays the same, medulla decreases)
  + explains why new neurons form the outermost layers of the cortex

Question 10

disadvantages of large brain size

Answer 10

• long gestation period + difficult birthing
• prolonged dependence on parents
• high metabolic cost
• complex genes are vulnerable to mutation

Question 11

theories of large cortex development

Answer 11

1. social brain hypothesis:
   - larger brain is needed to maintain social rela between similar individuals
   - correlation between clique size and cortex size relative to overall brain size (primates)
2. skill development + innovation:
   - large brain has adaptive advantages:
   + increased survival + ability for group interaction (humans)
   + innovative behavior, use of tools, and social learning (all primates)
   + adaptive to diverse changes of envi
3. sexual selection:
   - intersexual: members of one biological sex choose mates of the other sex to mate with (e.g. female birds choose males)
   - intrasexual: members of same sex compete for access to mates
   + e.g. elephant seal: males fight to have dominance of all females -> evolve bigger brain and body to fight rivals
   + Bower’s birds: build bowers/display arenas -> prettier, more favorable to females -> develop bigger, more mature brain
   + songbirds: larger song repertoire -> bigger cortex -> more females

Question 12

evolutionary adaptation of mate choice in humans

Answer 12

• females:
  + usually choose males based on intellect (e.g. sign = humor)
  + BUT during fertile period: more likely to choose someone with bigger muscles (healthy)
• males:
  + universally choose females with good waist:hip ratio
  + small waist = less fat = healthier, in peak of reproduction
  + large hips = better for childbirth

Question 13

evolution of human cortex vs. genes

Answer 13

• humans have more developed and complex cortex + intelligence NOT because we have more or different genes but because of gene expression level
• DNA:
  + coding region: transpire genes to RNA -> protein -> cell behavior (e.g. enzyme production)
  + non-coding region: DIFFERENT for individuals and species; regulate genetic expression (e.g. turn on, shut off, etc.) -> different personalities and individual attributes
• human brain = more convoluted comparing to mouse brain
  + increase in expression of the gene beta-catenin -> cortex development (bigger, more convoluted, better at problem-solving) – transgenic mice (with human gene inserted during embryonic state)
• differences in human skin color, facial features, stature, culture, etc. are due to environmental and ecological habitat differences
  + we continue to change envi (e.g. develop cities, global warming) -> brain tries to adapt