Natural and Artificial Selections

Artificial selection

humans select for desirable traits in agricultural products or animals, rather than leaving the species to evolve and change gradually without human interference

Consequences of artificial selection

reduces genetic diversity: gene pools of certain species

monoculture and its downsides

• planting of same species over large areas

• one pest or disease can wipe out all the crop

• no variations leaves crop susceptible to attack

Natural Selection

• also known as differential reproduction

• individuals with favourable traits are more likely to leave more offspring better suited for their environment

natural selection depends on 4 phenomena:

• variation

• competition

• survival of the fittest

• gradual change

variation

• characteristic of natural selection

• members of a population have slight differences among them

• much of variation is heritable

• variations MUST exist for advantages to occur

• variations affect survival and reproduction

• differences in height, eyesight, beak shape, egg production rate, etc

competition

• characteristic of natural selection

• populations tend to create more progeny than can survive

• progeny must compete for essential resources such as food, nesting sites, mates, etc.

survival of the fittest

• natural selection characteristic

• better adapted individuals are more likely to survive and reproduce

gradual change

• natural selection characteristic

• advantageous traits become mire common over a long period of time

fitness

• the contribution an individual makes to the gene pool of the next generation

• high fitness: individual produces lots of viable offspring

• low fitness: individual produces few or no offspring

need and wants in evolution

there are no needs and wants in evolution, you either have a variation or die

peppered moth natural selection

the dark form can camouflage on dark backgrounds

antibiotic resistance bacteria natural selection

when bacteria is exposed to antibiotics, only the resistant bacteria survive and produce more resistance bacteria

selective advatange vs. selective pressue

Selective pressure occurs when environmental conditions select for certain characteristics of individuals and select against other characteristics. A selective advantage is a characteristic that improves an organism’s chances of survival, usually in a changing environment