CHAPTER 16 NOTES
Return to England (1836-1859):
· Studied all of the data that he collected and realized the animals found on the Galapagos Islands were found no where else in the world.
· He realized that species from the South American mainland gradually became modified over time.
· Wrote the essay On the Origin of Species (1859) which proposed the mechanism for evolution he called Natural Selection.
· Prompted to publish when another scientist, Alfred Russel Wallace, mailed him a manuscript proposing the same theory.
Darwin discovered that variations in organisms were VERY important.
· Darwin realized that members of each species vary from one another in important ways.
· Observing breeders, Darwin noted that they would use genetic variation to improve crops or livestock. Darwin called this artificial selection.
· Artificial selection: nature provided the variation and humans selected those variations that they found useful.
· Darwin next compared artificial selection to what happens in nature. From this comparison, he developed his theory of natural selection.
5 major points to natural selection:
1. Genetic variations exist in populations.
· Some variations are more favorable than others.
· These variations are inherited.
2. Organisms produce more offspring than can survive.
· Those that do not survive, do not reproduce.
3. Overproduction of offspring forces competition for resources.
· Darwin called this the struggle for existence.
· Not all offspring can possibly survive.
4. Individuals with favorable variations have more “fitness” and are more likely to survive and pass those variations on to their offspring.
· Darwin called this survival of the fittest.
· Fitness is the ability of an individual to survive and reproduce.
· Organisms with low fitness do not survive and therefore, do not reproduce.
· Populations gradually change or evolve toward the favorable variations over time.
5. Species alive today are descended with modification from ancestral species that lived in the distant past.
· Darwin called this descent with modification.
· Common descent means that all living things belong to a single “tree of life”.
Adaptations: any inherited trait that increases the chances of survival and reproduction of an organism.
· Adaptations increase an organism’s “fitness”.
Examples: Mimicry- one species mimics the appearance of another.
The viceroy (a non-toxic butterfly) mimics the coloring of the supposedly toxic Monarch butterfly.
The bubblebee moth (harmless) mimics the bubblebee.
Bubblebee Moth Bubblebee
Camouflage- species blend in with surroundings.
Leopard Ground Squirrel