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Mechanisms

 

There are three primary sources of genetic variation, which we will learn more about:

  1. Mutations are changes in the DNA. A single mutation can have a large effect, but in many cases, evolutionary change is based on the accumulation of many mutations.

  2. Gene flow is any movement of genes from one population to another and is an important source of genetic variation.

  3. Sex can introduce new gene combinations into a population. This genetic shuffling is another important source of genetic variation.

 

Sexual selection acts on an organism's ability to successfully reproduce  with a mate.

 

Artificial selection is a process in which humans consciously select for or against particular features in organisms. 

An adaptation is a feature that is common in a population because it provides some improved function.  Adaptations can take many forms; they can be behaviors, or proteins, etc.

Coevolution is used to describe cases where two (or more) species reciprocally affect each other's evolution. This tends to happen when species interact closely with one another in a predator/prey relationship, mutualistic relationship, or competitive relationship. 

 

 

Patterns

 

Two characters are analogous if the two lineages evolved them independently.

A homologous structure is one that is inherited from a common ancestor.

 

 

Speciation

 

A species is often defined as a group of individuals that actually or have the potential to interbreed in nature. A species is the biggest gene pool possible under natural conditions. Speciation is a lineage-splitting event that produces two or more separate species. 

 

Causes of speciation include geographic isolation and reduction of gene flow. 

 

Reproductive Isolation

Offspring inviability or sterility

Lack of “fit” between sexual organs

The evolution of different mating location, mating time, or mating rituals

 

Cospeciation: If the association between two species is very close, they may speciate in parallel.

 

 

Microevolution

 

Evolution on a small scale — within a single population. Population is a group of organisms that interbreed with each other, meaning they all share a gene pool. Evolution is sometimes defined as a change in gene frequency within a population.

Mechanisms of microevolution include mutation, migration (or gene flow), genetic drift, and natural selection.

 

 

Macroevolution 

 

Evolution on a grand scale. It’s not quite easy to see macroevolutionary history, because there are no first-hand accounts that you can read to get the information. Instead, scientists examine and analyze evidence such as geology, fossils, and living organisms to figure out trends and transformations such as the origin of mammals and the radiation of flowering plants. 

 

Once scientists figure out what evolutionary events took place, they try to figure out how they happened. Evolutionary mechanisms such as mutation, migration, genetic drift, and natural selection explain many of life’s wonders and are also the reason many of these huge evolutionary changes took place. 

 

Patterns in macroevolution are basically "what happened when." All of the changes, diversifications, and extinctions that happened and are still happening in life are the patterns of macroevolution.

 

  1. Stasis: Lineages in life that don't change much for a long time.

  2. Character change: Lineages can change quickly or slowly. Character change can happen in a single direction, such as evolving additional segments, or it can reverse itself by gaining and then losing segments. Changes can occur within a single lineage or across several lineages.

  3. Lineage-splitting (or speciation)

  4. Extinction

 

 

Source

http://evolution.berkeley.edu/evolibrary/article/evo_01

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