Lamarck's hypothesis

Evolution is the process by which populations of organisms change through time, eventually forming new species. This idea was originally put forward by Jean Baptiste Pierre Antoine de Monet de Lamarck in the early nineteenth century, but theories surrounding the concept have changed significantly since Lamarck's time. Lamarck's hypotheses contained many pseudo-spiritual elements that meant the evolution would not be accepted until Charles Darwin published Origin Of Species in 1859(see below). These spiritual elements included the idea that organism blueprints had always effectively existed, waiting to be used and that organisms positively strove to evolve.

'Lamarckism' today is usually used to refer to another of Lamarck's hypotheses, that acquired characteristics can be passed on to offspring (eg- That if a giraffe stretches its neck to reach some leaves, its offspring will be born with a longer neck). This method of passing on characteristics has not been proven, and is thought to be false by almost all modern biologists.

Natural Selection

It wasn't until Charles Darwin's book Origin Of Species was published in 1859 that a mechanism for Evolution was introduced. This mechanism is Natural Selection, and was discovered separately by Charles Darwin and another biologist named Alfred Wallace, who was a contemporary of Darwin. The theory goes like this:

Organisms have many characteristics, some are useful to their survival and prospects of having children, some a hindrance. ¹ If these characteristics cause organisms to die before they have had offspring, these characteristics will no longer be found commonly. Those characteristics that are helpful will be found more commonly, as organisms with them will have more offspring. As this continues, the characteristics found in a population will change through time. If the population is split in two, say by a river suddenly forming halfway through its territory, two separate species may be formed, as different characteristics may be useful on one side to the other.

Gregor Mendel's genes

Gregor Mendel was an Abbot and gardener who started spotting in pattern in the way that characteristics were passed on from a plant to its offspring. He theorised that some characteristics were controlled by two 'genes', one of which would be passed on to offspring. The offspring would get another from its other parent. A good example of this (but not one that Mendel knew about) is human eye colour. Alleles (that is, different possibilities for the same gene) for eye colour include brown and blue. Someone with two brown alleles have brown eyes, someone with two blue alleles have blue eyes, but if they have one of each, they also have brown eyes. This is because brown is dominant over blue. This helps to explain why there are more brown eyed people than blue eyed.

At first, Darwinists rejected Mendel's gene hypothesis, claiming it contradicted Darwin's pet theory that the organism's recipe was found in the blood, and simply mixed and diluted. Eventually, however, it was realised that the gene theory did not contradict evolution, but was essential to it.

Crick and Watson

James Watson and Francis Crick were the scientists responsible for discovering the medium which held the genetic code, namely DNA or DeoxyriboNucleic Acid. Darwin had previously theorised that the genetic code might be stored in the bloodstream, but experiments with blood transplants proved otherwise.
Watson and Crick discovered that the DNA molecules were coiled into double helices

Richard Dawkins

It was Richard Dawkins that popularised the "gene's eye view" in The Selfish Gene, published in 1976. Using this way of looking at evolution, it is genes that are seen to be the reproducers rather than the organisms, the organism being something of a digression. Some have found this view to be depressing, one reader claimed not to have been able to sleep for some time after reading the book.

Punctuated Equilibrium

Formulated by Niles Eldredge and Stephen Jay Gould, this theory is contoversial to some. It states that most of the time, evolution in a state of 'stasis', that is, no changes are happening, but then evolution suddenly moves into a higher gear. The population will change massively in a short time, and a new species will form.

While technically evolution should only refer to biological evolution, it is occasionally used by other fields, to find out more click here.