What Was Important About Darwin's Discovery?
Darwin provided overwhelming evidence for natural selection in his famous book, The Origin of Species. After many years of sailing around the world as a passenger on the ship, The Beagle, Darwin had collected numerous specimens of sea and island life and had made many observations of plants and animals in their natural environment.
He documented the relationships between the environment and the structures and functions of plants and animals that gave them the ability to survive and thrive in such environments. The careful observations he made on plants and animals caused him to realize that each species had its own "niche" in the environment. "Niche" is a combination of the role, function, and place of an organism in the environment. Darwin's train of thought went like this:
Thus, the niche exerts a selection pressure. Only individuals that have genes that make them fit and adapted to the niche can survive. If only a few members of a species are adapted, the species may not survive.
But the effect of natural selection is anything but random. If the selection forces of niches dictate what it takes to survive in the niche, that is hardly random. Not all possibilities are equally likely. The chance for any organism to fill a niche is not 50:50.
Even if genetic mutation is purely random (which is probably not the case), natural selection is not random.
If several species can survive in the same niche, then competition among species becomes a factor. One or more species may be forced out of the niche by individuals who are more fit for that environment. None of this is random.
Why Scientists Think Natural Selection is So Important
For scientists, natural selection is a unifying principle that is consistent with all biological knowledge.
Natural selection is the only possible mechanism, based on observable evidence, that can explain how the environment can determine which species can survive and which cannot. Life is precious and fragile. Adapt or die. Anything that we humans do to the environment can change natural selection forces and thus create the risk of driving species into extinction. As we have seen with dinosaurs, for example, changing the environment may open previously occupied niches that can be occupied by new species that have the genes that can make them fit for that environment.