Darwinism and Natural Selection (Notes Starting on Packet Page 19)

Theories of Evolution Evolution is change in the heritable traits of populations over successive generations. Biological evolution is descent with modification. Microevolution = changes in gene frequency in a population from one generation to the next Macroevolution = the descent of different species from a common ancestor over many generations

What is a Species? A group of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups. Each species evolves independently A group that is reproductively isolated is unable to breed successfully outside the group.

What is a population? All the organisms of the same species, which live in a particular geographical area, and have the capability of successfully interbreeding.

Jean-Baptiste Lamarck French scientist (1744-1829) 1809 published one of the first hypotheses on evolution

Lamarck proposed that organisms could alter structures by use or disuse (Acquired Traits) This would then be passed on to offspring Ex. Fiddler crabs increased the size of their claw with constant use Proved incorrect

Lamark’s Giraffe

Charles Darwin English naturalist (1809-1882) 1831-1836 was on a five year journey on the HMS Beagle Collected and observed organisms for many years Made his most famous observations on the Galapagos Islands

Charles Darwin Conclusions were published in 1859 in On the Origin of Species by Natural Selection Concluded that variations were the result of reproduction Variations that were an advantage would be passed on

Darwin’s Theory of Natural Selection Mechanism for change in which organisms survive, reproduce, and pass their variations on to the next generation Also known as “Survival of the Fittest”

Darwin’s Theory of Natural Selection Organisms without the variations are less likely to survive Adaptation - any inherited trait that helps an organism survive in its environment Fitness- the ability of an organism to survive and reproduce in its environment.

Decent with modification Each generation of sexually reproducing animals mixes the genes of its parents, creating variation in the descendants' genes and physical forms. It's one of several genetic processes that modify populations of organisms over time. 

Natural Selection Darwin's explanation for how species changed over time.

Darwin’s 5 Points Variations exist within a population. Some variations are favorable. More offspring are produced than can survive. (Struggle for survival) Organisms with favorable traits (variations) are more likely to survive and reproduce. Over time, a population will change to have more of these favorable traits.

Word Sort (Bottom of page 20) Use the following words to fill in the blanks. You will only use each word once. Nature Long Predators approaching Perish Longer Reproduce Variation Longer Genes Fittest Longer Shorter Longer Environment Leaves in trees

Types of Selection (to be used with homework on page 23) Directional selection: a mode of natural selection in which a single phenotype is favored, causing the allele frequency to continuously shift in one direction Disruptive selection: (or diversifying selection) a mode of natural selection in which extreme values for a trait are favored over intermediate values Stabilizing selection: a type of natural selection in which genetic diversity decreases as the population stabilizes on a particular trait value