Theory of Natural Selection:. Darwin’s explanation for HOW evolution works. VOYAGE OF THE HMS BEAGLE : 1831 - 1836. Overpopulation (overproduction)- animals produce more offspring than survive. Variation - animals of the same species are different Change in environment-
Darwin’s explanation for HOW evolution works.
Variation- animals of the same species are different
Change in environment-
a) Biological - food, predators, shelter, etc.
b) Physical…water, oxygen, temp, etc.
4. Struggle for existence- competition for water, food, & shelter
5. Survival of the fittest- the best adapted & strongest tend to survive longer & produce more offspring
6. Inheritance- favored/best fit/selected variations (characteristics) are passed on to offspring.
7. New species arise- “selected” individuals grow in number and become a new species that cannot reproduce with original species7 Steps to Natural Selection
Darwin’s Observation: 13 or so species of finches on different Galapagos islands; these finches resembled the South American (mainland) finches more than say finches in Asia….
Human hand, cat limb, whale flipper, bat wing - they all have the same basic bone structure and design; So they have ALL evolved from a common ancestor with a similar ‘limb design’.
B) HOMOLOGIES –
C) Vestigial organs, structures that are not used, but which had important functions in ancestors - still retained in descendents, so evolution/change has occurred.
Some Alleged Vestigial Organs in Man
Coccyx (tail bone)
Nictitating membrane of eye
Nipples on males
Nodes on ears "Darwin's points"
Ear muscles for wiggling
Artificial Selection: The selective breeding of domesticated plants and animals to encourage the occurrence of desirable traits.
Mutations: Changes that occur in the hereditary material
Mutant: The new form that survives a mutation and passes this trait on to offspring
Adaptation: A favorable variation within a species that may help an organism survive