Panthentic, I don't know if you're still going to be around or not, but I'll keep posting in the hope that maybe someone will learn something new.
Introduction to evolution:One thing I want to make clear from the get-go, evolution cannot and does not try to explain how life originated. In its simplest definition, evolution is genetic change over time. Natural selection, endosymbiotic events, gene acquisition, gene recombination, gene mutation, and pre-cellular events are all the proccesses of evolution which result in new species emerging over time. The theory of evolution has been revised countless times since Darwin as new evidence emerges. These revisions have made the theory more accurate in making predictions.
As the genes of a group change, they may split into different species, typically as a result of physical isolation. As their evolutionary paths grow more distant, they grow more and more different. This means that some species are more closely related genetically to some species than other species. This can be observed by coding the DNA for various species. This is why the evolutionary tree is like a branch rather than a ladder. Sub-species are constantly splitting off from the main species. There are no “higher” or “lower” organisms—only organisms that are better or not better at surviving a given condition.
Evidence of speciation (one group becoming a different species from the main group):Around 1500, mice were introduced to the island of Madeira. Six distinct populations of mice were found containing chromosomal differences that prevent breeding with one another.
In 1905, De Vries found a variant of Oenothera lamarckiana (evening primrose) that had a chromosome number of 2N = 28. This variety could not breed with the standard of 2N = 14. It became a new species.
Three species of wildflowers were introduced to the US from Europe around 1900. Within a few decades their populations grew and they began inhabiting the same areas, yet they did not produce fertile offspring (definition of a species).
There is a fruit fruit fly which is a parasite of the hawthorn tree. About 150 years ago, some of these flies began infesting apple trees. The flies breed on either apples or hawthorn apples, but not both. Each variety of fly can be forced to breed (sperm and egg can produce viable offspring) but they do not do so naturally in the wild. This is evidence of speciation in progress.
A naturally occurring speciation of a plant species was observed in Oregon. You can read it here: Gottlieb, L. D. 1973. Genetic differentiation, sympatric speciation, and the origin of a diploid species of Stephanomeria. American Journal of Botany 60(6):545-553
There are so many other examples (with sources from scientific journals) which can be found at
http://www.talkorigi...speciation.html. Unforunately I’m not a biologist and some of the explanations are difficult to understand.
Edited by outsidedream86, 22 July 2010 - 01:53 AM.
