Formation of Species 16.3 pp. 309-312 Populations evolve, individuals do not evolve. Speciation = formation of new species of organisms by evolving from an ancestor Morphological Concept: Morphology = internal & external structure and appearance • Morph = change the look • Plus: Convenient, works with extinct species • Minus: Easy to make mistakes Formation of Species 16.3 pp. 309-312 Not this case: Biological Species concept = individuals of a population can successfully interbreed and cannot interbreed with other populations • Offspring are fertile • Plus: testable for living species; improved by DNA analysis • Minus: can’t apply to nonliving organisms Formation of Species 16.3 pp. 309-312 Isolation = populations are separated which may lead to speciation Ways to separate: Geographic isolation = different places Temporal isolation = different times Reproductive isolation = don’t mate Formation of Species 16.3 pp. 309-312 2 categories of Reproductive Isolation: 1. Prezygotic = before fertilization (before a zygote) – Different behavior – Different times (temporal) – Different habitats (geographic) 2. Postzygotic = after fertilization (after a zygote) – Mutation – Infertility of offspring Formation of Species 16.3 pp. 309-312 Rates of Speciation = how fast does a new species evolve • Rough average is 1 every million years but this can vary greatly • Depends on selection pressures in the environment Formation of Species 16.3 pp. 309-312 Rates of Speciation 1. Gradualism = slowly over time (~ million years) – Mutation – Isolation 2. Punctuated Equilibrium = periods of sudden evolution caused by extreme selection pressures, followed by periods of no evolution (~ thousands of years)