In order for a species to survive it must have variety within it's genotype to cope with an ever changing environment. If an organism can not adapt to these changing environments it will eventually become extinct.
If we are lucky enough to recognize a species is near extinction it can be put on an endangered species status. The Manatee and Karner blue butterfly are examples of such organisms.
The Father of Evolution is Charles Darwin. He worked on the HMS Beagle as the ship's Botanist in the 1830's and collected many species of plants and animals. Over a 50 year period of analyzing these specimens he postulated the theory of natural selection.
There were others of importance such as Lamarck who is unfortunately only remembered for his incorrect theory of inheriting acquired traits and not for all the great work that he did.
Evolution on a large scale is called macroevolution.
Example: All the mammals in Australia (monotremes and marsupials)
Evolution on a small scale from generation to generation within a species is call microevolution.
Example: Adaptive radiation of Darwin's Finches on the Galapagos Islands and Industrial melanism of the English moth.
The proof of evolution is the fossil record. Generally with the oldest and simplest fossils found on the bottom of undisturbed sedimentary rock strata. By examining these specimens we can see a gradual change in species over a long period of time. This is called gradualism.
Sometimes species will remain the same for a long period of time and then change very quickly. This is usually the result of some catastrophic disaster like an earthquake or volcano. This type of evolution is called punctuated equilibrium. The actual process in the evolution of a species probably envolves both.
This is a fancy way of stating that how we develop as an embryo reflects the organisms from which we may have evolved. Ex. Humans have gills and a tail early in our embryonic development.
These structures have a common origin but have evolved specific functions for their specific organism.
Example: The flipper of a whale and the wing of a bat. Insects are arthropods and birds are vertebrates.
The wing of a bird and the wing of a butterfly are examples of analogous structures. Similar functions but NOT structurally related.
Evolution toward each other would be convergent and evolution away from each other is divergent evolution
The most widely accepted theory of the origin of life is the Heterotrophic Hypothesis. It tries to depict what the Earth was like billions of years ago. A "soup" with NO free oxygen. Briefly it states that the first organisms to evolve were anerobic heterotrophs. This was followed by the autotrophs that released oxygen into the air as a waste product of photosynthesis. Finally the last to evolve were the aerobic heterotrophs. They were able to utilize the free oxygen made available by the autotrophs. Thus the last to evolve were aerobic heterotrophs like us.
New discoveries are always being unearthed...The Sauropod was discovered in the summer of 1999 in Oklahoma. It was 30 times larger than the giraffe.
The current belief is that between 8 and 14 million years ago the common ancestor to the ape and human evolved. Mitochondrial DNA has proven that this occurred in Africa. These early "Humans" are called HOMINIDS. The Australopithecus were one the earliest hominids to be bipedal. (Walk on 2 feet) Again the fossil record is proof of human evolution. The recent discovery of 6 million year old Australopithicus in Africa is the oldest to date. One of the most important advancements was the increase in the size of the human brain. Although this is not the only factor in our advancement as a species it was crucial. Brain size is not alone the most important factor. If this were the only factor the blue whale would be the most advanced technological species on Earth. It has been proven that Neanderthal and Cro Magnon both had similar sized brains. Yet Cro Maganon is considered more advanced or modern due to it's much more sophisticated use of tools.(technology)
The oldest form of Homo sapien was found to be about 100,000 years old. It was also found in Africa.
New discoveries may alter our current perception of how all species evolved. A scientist can never be satisfied unless they have absolute proof beyond any doubt or exception. Scientists can not assume anything.