Selective breeding & direct observation experimental evolution; rapid evolution in nature

1. marine copepod species • invaded freshwater 60 yrs ago • marine populations can’t • tolerate freshwater • invaders had to evolve • tolerance to freshwater Selective breeding & direct observation experimental evolution; rapid evolution in nature we’ve also seen rapid evolution of antibiotic resistance, pesticide resistance Teosinte

2. Fossil record – including transitional forms Archaeopteryx

3. Charles Darwin ends the debate Upon returning home, Darwin began to work through his notebooks from the voyage and began to consider how species could change. Influenced by reading: Charles Lyell - geologist; emphasized uniformity through time: slow gradual change leading to large accumulated change Adam Smith - economist; thought competition could regulate society Thomas Malthus - economist; potential for human population growth; observation of overproduction of offspring by plants and animals

4. Charles Darwin ends the debate • Darwin formulates natural selection as the mechanism of evolution • more offspring are produced than the environment can sustain (Malthus) • individuals vary (direct observation, other naturalists) • individuals compete for limited resources (Smith)* • individuals with favorable variations survive • variations can be inherited** • differences in survival could lead to subtle changes in traits which, if accumulated over long periods of time (Lyell), could to lead to new species * We now know that competition isn’t the only source of natural selection. ** In Darwin’s day, nobody understood inheritance because Mendel’s work wasn’t discovered until 1900.

5. Charles Darwin ends the debate… but not without being prodded by some scientific competition Meanwhile, Alfred Russel Wallace… - had been on collecting trips to the Amazon and Malaysia - had read Malthus - independently came up with the concept of natural selection in 1858 - promptly sent a letter explaining his ideas to Darwin (who still hadn’t gone public with his theory) Darwin’s friends brokered a compromise… - the ideas of Wallace and Darwin were presented together in 1858, - in 1859 Darwin published a “short” version of the book he was working on: On the Origin of Species by Means of Natural Selection

6. Darwin’s Four Postulates • Individuals within species vary. • Some of these variations are heritable. • More offspring are produced than can survive. • Survival and reproduction are nonrandom. • The individuals that survive & reproduce the most are those • with variations that best suit their environment. This process, natural selection on individuals, results in changes in the proportion of the population with certain variations.

7. Some definitions fitness – organism’s ability to survive and reproduce in its environment adaptation – trait that increases fitness and has evolved by natural selection adapt, adaptation – process of evolving traits, through natural selection, that increase fitness adaptive – describes a trait that increases fitness exaptation (preadaptation) – trait that increases fitness through a particular function, but has not evolved for that function; an existing trait that is used for a new function constraint – factor that slows or prevents evolution of an optimal trait