What happens if an animal is not well adapted

Again and again we are told how perfectly animals are adapted to their environment. It is, however, seldom true. It appeared perfectly well adapted to its environment. Until the grey squirrel arrived, that is, and proved itself rather better adapted to broadleaf forests thanks, in part, to its ability to digest acorns.

Botched jobs are common, in fact. As this example shows, evolution is far more likely to reshape existing structures than to throw up novel ones. The lobed fins of early fish have turned into structures as diverse as wings, fins, hoofs and hands. We have five fingers because our amphibian ancestors had five digits, not because five is necessarily the optimal number of fingers for the human hand. Many fossils of different kinds of horses have been discovered, and paleontologists think that the earliest ancestor of the modern horse lived in North America more than 50 million years ago.

This animal was a small padded-foot forest animal about the size of a dog. If you saw one next to a modern horse, you might not even think the two were related! As time passed, the climate of North America became drier, and the vast forests started to shrink. Grasses were evolving, and the amount grassland was increasing.

Horses adapted to fill this new grassland niche. They grew taller, and their legs and feet became better adapted to sprinting in the open grasslands. Their eyes also adapted to be further back on their heads to help them to see more of the area around them. Each of these adaptations helped the evolving grassland horses to avoid predators. Their teeth also changed to be better adapted to grinding tough grassland vegetation.

Have you ever wondered what purpose the "dew" claw on the inside of a dog's paw serves? And why do men have nipples? Evolution is all about creatures gradually adapting to their environment, right? For instance, some non-adaptive, or even detrimental, gene variants may be on the same DNA strand as a beneficial variant.

By hitching a ride on the same DNA strand as the useful variant, a non-adaptive gene can quickly spread throughout a population. Some of these mutations will be harmful, and will probably be eliminated by natural selection. Learn More Life's Grand Design.

Evolution does not stop once a species becomes a species. Every population of living organisms is undergoing some sort of evolution, though the degree and speed of the process varies greatly from one group to another. Populations that experience a major change in environmental conditions, whether that change comes in the form of a new predator or a new island to disperse to, evolve much more quickly than do populations in a more stable set of conditions. This is because evolution is driven by natural selection, and because when the environment changes, selective pressures change, favoring one portion of the population more heavily than it was favored before the change.

Evolution is always happening, though often at rates far too slow to be observed in a matter of days, weeks, or even years. The effects of evolution can be felt in almost every aspect of our daily lives, though, from medical and agricultural dilemmas to the process of choosing a good mate.

In medicine, there's the question of how long the antibiotics we take now will remain effective, given the relatively fast rate at which bacteria can evolve resistance to drugs.