5.1 Evidence for evolution Cheat Sheet by Arsh.b

Evolution is a change in the heritable charac­ter­istics of a species over time. As heritable charac­ter­istics are encoded for by genes, and may be transf­erred between genera­tions as alleles, biological evolution is a change in the allele frequency in a popula­tion's gene pool over successive genera­tions.

Selective breeding is a form of artificial selection, whereby man intervenes in the breeding of a species to produce desired traits in the offspring. It provides evidence for evolution as targeted breeds can show signif­icant variation over a (relat­ively) short period of time.

Selective breeding of domest­icated animals has also resulted in the generation of diverse breeds of offspring. Examples include dogs, horses and cows.

Within a population of any given species, there will be genetic variation that is typically continuous and follows a normal distri­bution curve. This is because the rate of change is gradual and cumula­tive.

The degree of divergence between two species will depend on the time since the isolation has occurred. Popula­tions the separated recently will have less variation than those who separated for a longer period of time.

The degree of divergence between reprod­uct­ively isolated population will gradually increase the longer they are separated. As the genetic divergence between these species increases, their genetic compat­ibility decreases, eventually resulting in them being unable to interb­reed.

A fossil is the preserved remains or traces of any organism from the remote past. The fossil record is the totality of all fossils, both discovered and undisc­overed.

The fossil record is incomplete due to the specific set of circum­stances required for an organism to be preserved, as well as the fact that only the hard parts of organisms are preserved. Transi­tional fossils demons­trate the interm­ediary forms that occurred over the evolut­ionary pathway taken by a single genus.

Compar­ative anatomy of groups of organisms may show certain structural features that are similar, implying common ancestry. Anatomical features that are similar in basic structure despite being used in different ways are called homologous struct­ures. Homologous structures show adaptive radiation, as several species diversify to utilise a specific unoccupied niche.

A classical example of homologous structures is the pentad­actyl limb in a variety of different animals. Mammals, birds, amphibians and reptiles all share a similar arrang­ement of bones in their appendages based on a five-digit limb

In an unpolluted enviro­nment, the trees are covered by a pale-c­oloured lichen, which provides camouflage for the lighter moths.

The frequency of the two different forms of peppered moth is dependant on the enviro­nment and evolves as conditions change.
- Before the industrial revolu­tion, the enviro­nment was largely unpolluted and the lighter moth had a survival advantage
- Following the industrial revolu­tion, the enviro­nment became heavily polluted, conferring a survival advantage to the darker moth
- Recent enviro­nmental policies in Europe are reducing pollution levels, altering the frequency of the two popula­tions once again.