Lamarck was the first biologist to propose a mechanism for evolution. He proposed that organisms acquired features as they needed them. A giraffe would require a long neck because it strove to eat leaves high up in the trees, and birds that did not like swimming, but collected food in shallow water, would develop long legs and become waders. Lamarck, at times, ascribed the process of evolution to some inner mystical property of life.

Darwin, on the other hand, proposed the mechanism of natural selection as an evolutionary mechanism more acceptable to biologists. He defined the principle as follows: 

As many more individuals of each species are born than can possibly survive, and as, consequently, there is a frequently recurring struggle for existence, it follows that any being, if it vary, however slightly, in any manner profitable to itself under the complex and sometimes varying conditions of life, will have a better chance of surviving and thus be naturally selected. From the strong principle of inheritance, any selected variety will tend to propagate its new and modified form.ⁱ

This theory provided a mechanism for change over time, but it was not until the science of genetics had developed and the concept of mutations was understood that the concept could be developed into its present-day form, in which mutations provide the material for variation and variation becomes the substance upon which natural selection could feed.

The basic difference between Lamarckism and Darwinism is that Lamarck proposed that adaptations were acquired because organisms needed them, whereas Darwinism states that the adaptations developed by chance through mutations and selection takes place by natural selection. In a sense, natural selection becomes the driving force for change.

The basic Darwinistic view of origin by natural selection is upheld by most biologists today. They might vary on the mechanism of change, but the basic principles of Darwinism are deeply entrenched in current scientific thinking.

Science today leaves little room for a literal interpretation of the Genesis account, or the short chronology associated with it. At best, scientists might ascribe to some form of theistic evolution where God is seen as the originator of life and the mechanisms of evolution as the "creator" of the varied life forms in existence today. This theory proposes that God used evolution to create people and all the other living organisms on Earth. A basic problem with this theory, however, is that the Bible declares that death is a consequence of sin, whereas natural selection sees death as an underlying principle for change. In essence, the two worldviews of origin by evolution or special Creation seem mutually exclusive. 

In light of these differences, it is evident that it would take quite a degree of distortion to reconcile the two concepts. Indeed, the modern concept of scientific creationism is largely frowned upon, and even ridiculed, by the scientific community. Nevertheless, some new evidence strongly supports at least some of the arguments put forward by propagators of the Creation model, and there have been some major modifications in the thinking of even the uniformitarians. Even many geologists have come full circle in the past few years, accepting the possibility that some of the catastrophic events in our geological past may have had more than local significance.

Since scientist Luis W. Alvarez proposed in 1980 that an asteroid had collided with the earth and caused widespread destruction and extinction of species, there has been a greater acceptance of catastrophism as a causative agent in the shaping of geological features. Although the concept of a worldwide flood on the scale described in Genesis is still taboo, post-catastrophic floods are being regarded more and more as shapers of geological features that were previously considered to have developed as a consequence of uniformitarian principles over thousands or millions of years. One example of such a change of position is the story of the Columbia River Dry Falls which are now considered to have been shaped by catastrophic floods at the end of the last ice age.

Read about the age of the Earth.