Slide 1:Thinking about the Biology of Behavior Chapter 2 Evolution, Genetics, and Experience


Human Evolution :While Darwin was not the first to propose that species evolve, he was the first to compile supporting evidence (and to suggest how evolution works) Darwin presented 3 kinds of evidence Darwin argued that evolution occurs through natural selection Human Evolution


Human Evolution: Evidence for Evolution :Darwin’s evidence Fossil evidence of evolution Structural similarities among living species suggesting common ancestors Impact of selective breeding Direct observation of evolution in progress: Grant (1991) finches of the Galapagos islands changed dramatically after a single season of drought Human Evolution: Evidence for Evolution


Human Evolution: Evidence for Evolution :gdf Human Evolution: Evidence for Evolution What about behaviors?


HumanEvolution: :HumanEvolution: Evidence for Evolution (continued) Four kinds of evidence that species evolve


Evolution and Behavior :Evolution and Behavior Just as physical features can contribute to “fitness,” so do behaviors Some are obvious—the ability to find food, avoid predation, etc. Some are less obvious—social dominance and courtship displays


Course of Human Evolution :Course of Human Evolution Evolution of vertebrates Chordates have dorsal nerve cords Vertebrates are chordates with spinal bones Evolution of amphibians Bony fishes leave the water briefly Advantages include fresh water and new food sources


Slide 8:Course of Human Evolution (continued): Amphibians Recently discovered fossil of missing link between fish and land animals


Course of Human Evolution (continued) :Course of Human Evolution (continued) Evolution of reptiles Lay shell-covered eggs; covered by dry scales Can live far from water Evolution of mammals Develop mammary glands to nurture young Eventually no longer lay eggs: raise young in mother’s body Humans emerge from the order primates


Course of Human Evolution (continued) :Emergence of humankind Humans belong to family hominids, genus Homo First homo species emerged from Australopethicus 2 million years ago Homo sapiens emerged 200,000 years ago Course of Human Evolution (continued)


Slide 11:Course of Human Evolution(continued) The remarkably complete skull of 3-year-old Australopithecus girl. The fossil is 3 million years old.


Slide 12:Vertebrate evolution Thinking about Human Evolution


Thinking about Human Evolution (continued) :Thinking about Human Evolution (continued) Evolution does not proceed in a single line Humans have only been around for a brief period of time Rapid evolutionary changes do occur Fewer than 1% of all known species are still in existence


Thinking about Human Evolution (continued) :Thinking about Human Evolution (continued) Evolution is a tinkerer, not an architect— results are not perfect Not all existing behaviors or structures are adaptive Spandrels—incidental nonadaptive by-products (such as the human belly button)


Thinking about Human Evolution (continued) :Thinking about Human Evolution (continued) Not all existing adaptive characteristics evolved to perform their current function Exaptations – evolved to do one thing, but now do something else (such as bird wings) Similarities among species do not necessarily mean that the species have common origins


Thinking about Human Evolution (continued) :Thinking about Human Evolution (continued) Homologous structures – similar structures due to a common evolutionary origin Analogous structures – similar structures without a common origin Convergent evolution – the evolution of similar solutions to the same environmental demands by unrelated species


Evolution of the Human Brain :Evolution of the Human Brain There is no relationship between brain size and intelligence Brain size is generally correlated with body size More informative to look at relative size of different brain regions


Evolution of theHuman Brain(continued) :Evolution of theHuman Brain(continued) The brains of animals of different evolutionary age. The cerebrums are shown in yellow; the brainstems are shown in purple.


Evolution of the Human Brain (continued) :Evolution of the Human Brain (continued) The human brain has increased in size during evolution Most of the increase in size has occurred in the cerebrum Increased convolutions in the cerebrum have served to increase the volume of the cerebral cortex


Slide 20:Evolutionary Psychology: Mate Bonding Most species mate promiscuously Most mammals form polygynous mating bonds Humans form monogamous bonds Men value youth and attractiveness in mates Women value power and earning capacity