Natural Selection Lab 14

Evolution - Defined Evolution – a change in the genetic composition of a population over time. A change in the frequency of certain alleles. On a larger scale, evolution can be used to refer to the gradual appearance of all biological diversity.

A Mechanism for Evolution Darwin presented a mechanism for evolution – natural selection. Organisms that are in some way more successful at reproduction will pass on more of their genes. Over time the traits responsible for that success will become widespread in the population. This theory holds up very well!!

Natural Selection Natural selection occurs when organisms with particular heritable traits have more offspring that survive & reproduce.

Natural Selection Natural selection can increase the adaptation of an organism to its environment.

Natural Selection When an environment changes, or when individuals move to a new environment, natural selection may result in adaptation to the new conditions. Sometimes this results in a new species.

Natural Selection Individuals do not evolve; populations evolve. Evolution is measured as changes in relative proportions of heritable variations in a population over several generations.

Natural Selection Natural selection can only work on heritable traits. Acquired traits are not heritable and are not subject to natural selection.

Natural Selection Environmental factors are variable. A trait that is beneficial in one place or time may be detrimental in another place or time.

Natural Selection When natural selection is occurring, some individuals are having better reproductive success than others. Alleles are being passed to the next generation in frequencies that are different from the current generation.

Genetic Drift The smaller the sample, the greater the chance of deviation from expected results. These random deviations from expected frequencies are called genetic drift. Allele frequencies are more likely to deviate from the expected in small populations.

Genetic Drift Which allele was lost is due to random chance. Over time, drift tends to reduce genetic variation through random loss of alleles.

Natural Selection & Adaptation Natural selection is a way of altering the gene pool that results in adaptation. Genetic drift alters the gene pool but does not result in adaptation. Selection depends on variation.