The changing of some organisms from one species into another through a long process of genetic mutation over a period of time- mostly very, very long time. These new species are generally able to survive better in the ecosystem they find themselves in.
The Theory of Evolution by Natural Selection is a scientific theory that runs along side atomic theory, electrical theory, cell theory, gravitational theory, etc. It is a theory but by no means a guess- as the word theory is used in society. Remember, a scientific theory can only rise to that designation by being tested and challanged as many times as possilbe and having the theory hold up to the prediction. Scientific theories have a great amount of evidence and tested datat to support them.
Evolution has just that evidence and data. So why are some groups raising up the call for the theory of evolution to be denounced? There are many reasons- none of which fall as scientific reasons. For many, they believe that evolution tries to explain where life and the universe come from- thereby rendering their god insignificant in the creation of the universe and life. They are misguided. The theory of evolution cannot explain where life came from- only the process by which we have the huge variety of life. Some believe that their religion is the "right" one and therefore all other religions or concepts that they view as going against their view are wrong. Such is their belief system. Some are simply reacting to the "scientific left" who view their belief systems to be garbage and the delusions of overactive imaginations; so they retaliate in kind.
As I have tried to explina in class: . . . .
Time, don't we all wish we had more of it? Well, if you consider the history and age of the earth you may find that sentiment to be even more depressing! For many, we think of the time we are aware of as all the time of the Earth we need to be concerned with- and in many respects that might be true. However, the Earth is 4.6 billion years old and THAT is a long time to wrap our heads around. Most people can conceptualize hundreds of years- especially if they are history buffs. However, after that it becomes "a long, long time ago". Forget about conceptualizing 100,000 years, 1 million years, or a billion years!
The concept of evolution depends on the Earth being very old. During Darwin's time that ability to test and/or prove the age of the Earth was very hard to do and many people tried; each time coming up with older and older ages. Darwin himself thought the Earth to be very old; after witnessing fossilized sea life on top of mountains where no sea life was found lower down. He thought a very long time had to have happened to form mountains and such.
Thanks to radiometric dating using radioactive isotopes and chemistry we are able to date the rocks and strata we live on. That number to date is 4.6 billion years old! So lets put 4.6 billion years onto something we can conceptualized- a football field. . . . .
Geology and Ecology and Fossils
The fossil record was one of the first factors that started Darwin thinking about how the organisms of today may have come from organisms past. While riding with the Gouchos of South America he came apon a number of Giant Sloth skeletons. The animals that would have left those skeletons were NOT alive at the time and this was puzzling as Darwin had been taught that all animals were put on the Earth for now and all time- but these animals weren't! In addition, he noticed that the skeleton of a Capybara- a giant rodent that WAS living at the time- closely resembled the skeleton of the Giant Sloth. Hmmmm.
Today we know that the living creatures of the past may have left behind an impression or even the fossilized remains of their bodies. We call those remains fossils and fossils are frequently found in sedimentary rock. Sedimentary rock is rock that was laid down by calm forces creating layers or strata of earth. Caught between and in those layers or strata are the fossils.
If the strata was laid down without disturbance then the timeline of the fossils is easy; older fossils are lower and younger fossils are higher in the strata. In fact, the most recent fossils will, generally, bear a strong resemblence to the living creatures found in that geographic region.
If, however, the strata has been disturbed through the movement of the earth- like faults, earthquakes, the formation of mountains, rivers, lakes, oceans, erosion, etc.- then the fossil record will be jumbled and in need of analysis. In MOST cases, the fossil record is jumbled and in need of analysis!
When certain fossils are found in abundance and "suddenly" disappear in later layers or strata, we call that extinction. Extinction is common in the fossil record and is due to the inability of organisms to be able to adapt to their ecosystem quickly enough- if at all. . . .
Evidence for Evolution
In order for the Theory of Evolution by Natural Selection to be considered a scientific theory it must have verifiable evidence. The evidence for the process of evolution focuses on the concept of common ancestors from which current organisms have evolved from. The following evidence is based on the inheritance of genetic information from one generation to the next. Just like in a family, genes will be passed on to the young who will exhibit both a similarity of form and DNA- which shows they are related. The evidence for evolution, in no particular order, is as follows:
1. DNA: Every living organism on the planet shares four nucleic acids (adnenine, thymine, guanine, cytosine) in common. . . .
Charles Darwin, as he worked on his theory of evolution, noted that there needed to be some pressure that would select which organisms survived and which did not- in a given environment. His great break through came as he observed "pigeon fanciers" who would select which pigeons to breed together in the hopes of getting baby birds with particular traits. He also observed that farmers would do exactly the same thing with their animals and crops- choosing those "parents" that might give the farmer a better product in the offspring. For example, breeding a cow that produced a lot of milk or a horse that was very strong while hoping for offspring with the same or better traits. Breeds of dogs, he noted, were nothing but people mating two dogs together in the hopes of a new and unique type of dog. Maybe a new breed.
Artificial Selection, as we call it today, has been going on since the dawn of farming . . .
While evolution may be defined as genetically based (mutations and genetic change), natural selection is focuses on how those genetically based phenotypes interact with the environment and the individuals of the community. Nature "selects" which organisms will be able to survice in a given environment. The organisms themselves are not able to "will" or initiate physically change to meet shifts in the ecosystem where they live and this may cause them to die off. They may, however, change their behavior which could lead to further survival! In any case, a species may go extinct if they cannot adapt to the changes in the environment brought about by "mother nature" or humans!
Natural selection comes about by the ability of organisms to address four main points:
1. Over production: The ability to produce more offspring than will survive. This over production also allows for a greater potential for genetic mutation and potential beneficial change in a species (ie. insects, bacteria, amphibians may evolve quicker than humans, elephants, maple trees, etc.). The more the DNA is manipulated to produce new cells such as sperm and egg, the great the possibility that mutations will occur and the great the possibility a species may change. Again, this change is random and may help or harm a species survival. Genearlly, however, beneficial changes tend to be passed down from parents to offspring as those are the organisms surviving to reproducive adulthood!
2. Variation: Physical and behaviorial differences within a population. This is the genetic mutations mentioned above and, again, if beneficial will be passed down from parent to offspring. . . .
Human beings enjoy a long line of fossil evidence dating back 100,000 years. Beyond that are the hominids from which we evolved dating back almost 5 million years! In early 2000s more bones were unearthed that pushed the date back to 7 million years but more work needs to be done to verify that date.
Beginning at our earliest ancestors . . . .
Australopithecus (2.75 to 4.5 million years ago)
Australopithecus is a different Genus than us but of the same family. Australopithecus remains have been found on the Eastern coast of Africa in a place called the Great Rift Vally- specifically Oldivai Gorge. Australopithecus shares modified features with other great apes like the sagittal crest on top of the head (much smaller), large canine teeth (much smaller), and a face that is more shovel like without a protruding nose and a large jaw.
What puts Australopithecus in the family Hominidae is that it walked upright! It was bipedal and had hips and feet that were made for walking. This standing upright may have allowed Australopithecus to scan the area of high grass for predators, find food, walk great distances, and freed up the hands for carrying things it might have needed. All of this would have given Australopithecus an advantage in living in Africa. In addition, Australopithecus had a larger brain than that of other great apes- not much but enough to be significant. . . .