EVOLUTION
KEY IDEAS
1. A theory that explains how species have changed over time is Evolution
2. Natural selection – individuals that survive (favorable traits) can breed and pass on these traits
to offspring. Those w/ unfavorable traits die and are less likely to pass on traits
3. Those best adapted to environment will survive and pass on their traits (stronger, faster)
4. Overpopulation – producing more offspring than can possibly survive. Some die from lack of
food, predators, etc. (rabbits, bacteria, insects, fish)
5. Competition for resources happens between the same and other species. All organisms need
food, water and shelter but these are limited. Those best suited for environment will get the
resources and survive
6. Genetic variations cause differences among individuals of a species (longer legs, different
color). Traits that help an organism survive have adaptive value and generally get passed on
to the next generation
7. These good traits continue to pass on, outnumbering the old trait and eventually nearly all of
the population will have the trait
8. A changing environment is the driving force for evolution. Organisms adapt to new
environments to survive
9. Sources of variation in offspring are mutations (change in base sequence of DNA, most are
harmful) and genetic shuffling (crossing over in meiosis) giving large numbers of possible
combinations of chromosomes
10. Species are structurally different b/c of evolution, they are best suited to survive in their
environment (polar bear is white, survive in arctic, die in forest)
11. Vestigial structures (no longer used) give clues to an organisms past (leg bones in snakes, tail
bones in humans)
12. Behaviors effect evolution. Males battle to mate w/ females. Better traits get passed on to
offspring
13. Rate of evolution is effected by environment (stable = no evolution, changing = evolution), life
span (faster reproduction = more generations = faster evolution) and number of offspring (more
offspring = faster evolution)
14. Bacteria becoming resistant to an antibiotic. One bacteria is resistant (chance mutation), the
antibiotic kills off competition and bacteria quickly reproduces w/ less competition making larger
population of resistant bacteria
15. When an environment changes too quickly for an organism to adapt, extinction can occur
16. More variation w/in a species inc chances of survival if the environment changes