Psy155 Lecture #2 Notes: How Natural Selection Works

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PSY 155
Leda Cosmides

Reminders... • Genotype (the genes) vs. phenotype (what the genes code for) • 23 pairs of chromosomes (46 total) • 1/2 from mother, 1/2 from father • Genes = factories that build and regulator organisms • You can’t divide phenotype into parts coded for by genes versus parts coded for by environment • All aspects at all levels of an organism are joint product of genes and environment Who Are We? • Kingdom: Animalia • Phylum: Chordata • Subphylum: Vertebrata • Class: Mammalia • Order: Primate • Family: Hominidae • Genus: Homo • Species: Sapiens • Subspecies: Sapiens What Is Life? • How did organisms come to be the way they are? ◦ Design features (adaptations) ▪ Certain parts are there because they solve a problem ▪ Design features are adaptations ◦ There are also simply by-products (side effects of an adaptation) Phylogenetic versus Adaptationist Approaches • Phylogenetic perspective: all organisms and species are all related to one another, and to all other species, by common descent. ◦ This approach leads us to ask… ▪ How are we similar to our closest relatives? (ex: chimpanzees) • Adaptationist perspective: this is the most useful approach for psychologists because it emphasizes natural selection as the process that designs organisms. ◦ This emphasizes that natural selection can make species similar to one another OR different from one another ▪ Convergent evolution (ex: dogs and wolves are convergent in the sense that they both evolved to bark to protect their own territory) ▪ Divergent evolution Darwinism explains phenotypes • He wanted to know why we have the design features that we do • We have complex functional designs (ex: the design of the eye). How do these complex design functions simply come about? • Paley had an argument for God. He said: ◦ If you came across a watch on the beach and saw the complex design, you wouldn’t think it was made by the beach, you would think that someone made it due to the complexity (it must have been designed to fix something or serve some purpose). ◦ When you look at organisms, they show the same complex functional design or even more complex, and he said that just like the watch, someone must have made them (aka God) • Darwin asked: in the absence of a creator, how could complex functional design arise in the world? ◦ This is where he said that evolution was caused by natural selection, which created a causal account of the relationship between adaptive problems and the design features of organisms What Is Life? • Organism: self-reproducing machine (designed to reproduce itself) • Reproduction is the defining property of life • Any system capable of reproducing itself that is designed to do so = Living system ◦ Ex: Mr. Data from Star Trek ▪ He cannot reproduce so he isn’t alive from a Darwinian point of view •
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