Evidence for Biological Evolution

Evolution results from 4 factors:

Potential for a species to increase in number

Heritable genetic variation Due to mutations and sexual reproduction

Competition for limited resourcesReproduction of organisms better able to

survive in the environment

Inherited variation & Artificial selection Individuals of each species vary. Darwin argued that variation was important. In artificial selection, humans select from the

naturally occurring genetic variations in a species.

Example: Dogs: all descended from wolves Selective breeding

for color, hair, size, behavior

Interbreeding reduces genetic variation

Artificial SelectionWheat, corn, for

resistance to rust,fungi, etc. USDA spends $ to breed

new resistant varieties.Unintentional artificial selection

Antibiotic resistance in bacteriaPenicillin, Streptomycin, Tetracycline, etc.“Multidrug resistant” tuberculosis

Pesticide resistance in insect pestsDDT, Chlordane, etc.

Remember… Adaptation = any inherited characteristic

that increases an organism’s chance of survival Anatomical, physiological, behavioral Successful adaptations enable organisms to

become better suited to their environment. Fitness = the ability of an individual to

survive and reproduce in its specific environment. Result of adaptation.

Survival of the fittest = individuals with adaptations that make them better suited to their environment survive and reproduce.

Natural Selection Natural selection = the

traits being selected, and increasing over time, contribute to an organism’s fitness in its environment.

Results in changes in the inherited characteristics of a population, which increase a species’ fitness in its environment.

Evolution by Natural Selection

Darwin proposed that a type of artificial selection occurred in nature.

Members of each species compete regularly to obtain food, living space, and other resources. Selection removes (some) individuals with

unfavorable traits. Selection preserves (some) individuals with

favorable traits. The struggle for existence was central to

Darwin’s theory of evolution.

Common Ancestry Homologous “same” structures, different

fucntions Comparing the anatomy of fossils and living

organisms

All tetrapods have similar limb bones

Common Ancestry examples: All primates have 5 fingers Apes and humans lack a tail

Common Ancestry Embryological evidence suggests common

ancestry Homologous structures develop different functions

Common Ancestry

The early embryonic stages of a (a) lemur, (b) pig, and (c) human show strikingly similar anatomical features.

Common Ancestry: Fossil Record

The only record that species changed over time

Darwin’s Concept: Natural Selection Genetic variation exists within a population due

to mutations and sexual recombination Competition for resources yields the survival of

the fittest for a certain environmental condition Adaptations are changes in genetic traits over

time Natural selection favors traits (variations) that

make an organism more fit for its environment, leading to adaptations in a population over many generations.

Darwin’s Finches Galapagos Islands: 14 species of finches with one common ancestor Variety of beak

adaptations due to isolation of populations on different islands

Ongoing competition for resources