relationshiop between process of evolution and a mechanism

[rajvandam]

To start off with, just some basic terminology...

Evolution: changes occuring in populations of organisms over time

Populations: groups of organisms of the same species that live in a particular area... within these groups evolutionary changes are produced by various mechanisms of evolution

Mechanisms of evolution: things like natural selection and genetic drift are mechanisms of evolution.

Evolutionary changes are genetic, and environmental changes are not genetic.

Genetic variation: raw material of evolution... most natural populations have significant genetic varation.

The three mechanisms of evolution are:

1. gene flow
2. natural selecion
3. genetic drift

Gene flow: refers to changes that occur in the genetic composition of poplations as a consequence of migration of individuals among populations... for example, the population has all black hair, individuals with red hair move into the population, the genetic composition of the population has changed via gene flow

--> the absence of gene flow can cause evolution too, because if a large population gets separated into two populations and become isolated from each other, over time slowly both can evolve into separate species.

Natural Selection requires three things: 1. there must be variation in the population in some biological characteristic 2. different versions of the characteristic (eg long legs vs short legs) 3. the characteristic must be inherited by the offspring

changes in population are shown in new born offspring... individuals with characteristics that allow them to survive long enough to reproduce will have their characteristics represented in the next generation.

Biological factors of an organisms' environment includes: predators, diseases and competitors... physical factors of an organisms' environment includes: temperature, humidity and solar radiation. Any aspect of individual's environment can cause natural selection to happen.

Directional selection: Example... light fur coloured mice die more due to hawks eating them, so in the next generation dominant fur colour of mice shifts to dark

Evolutionary change that occurs in populations of organisms in response to natural selection is known as "adaptation", for example, long legs in antelopes are an adaptation for escaping predators.

Genetic Drift: is the third mechanism of evolution. It requires variation in a trait or characteristic within a population (like natural selection)... changes in genetic composition of populations occur from one generation to the next caused by random events... the genetic makeups are not favored or "selected"... example: wind pollination in a flower... a random factor (the wind), so not all members of population will reproduce in every generation.

Bottleneck/ founder effect: An example depicting this effect would be---> A current population represented by marbles has red, white and blue marbles... a natural disaster eliminates all of the red marbles and decreases the white marbles by a lot... when the new population grows back to the original size it was previously, it will mostly consist of blue marbles ---> and this is all due to pure randomness... the bottleneck effect has to do with natural disasters.

Man, oh man that was a lot of stuff... but evolution is a process with a lot of components to it, so I'm not really surprised... to summarize the relationship between the process of evolution and a mechanism:

evolution, populations, mechanisms of evolution (gene flow, natural selection, genetic drift), genetic variation...

the bottleneck/ founder effect.

[Darby]

This is just the simple beginner's version - don't imagine that the list of mechanisms is just 3 processes long...

[reetha25]

Biological (or organic) evolution is change in the properties of populations of organisms or groups of such populations, over the course of generations. The development, or ontogeny, of an individual organism is not considered evolution: individual organisms do not evolve. The changes in populations that are considered evolutionary are those that are ‘heritable' via the genetic material from one generation to the next. Biological evolution may be slight or substantial; it embraces everything from slight changes in the proportions of different forms of a gene within a population, such as the alleles that determine the different human blood types, to the alterations that led from the earliest organisms to dinosaurs, bees, snapdragons, and humans.
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reetha

http://www.biology-online.org