Adaptation

Adaptation is an externally or internally developed characteristic that helps the individual organisms to survive and reproduce. It is essential to natural selection and evolution because it one of the ways organisms respond to a changing environment. A well-known example of adaptation involves the development of resistance to certain antibiotics by a strain of bacteria.

For adaptation to occur, the genetic code must be malleable - that is, the DNA gets changed, for better or for worse, by mutation: processes including horizontal gene transfer, copying errors and translocation.

Failures
Adaptation is not always successful. Often times, the environment changes too rapidly to allow for adaptation. For example, if the population of a predator within an ecosystem increases, its prey may be wiped out before it can adapt. One well-known example was the dodo, which, if it could have adapted to protect itself from bullets and bayonets, might not be extinct.

The platypus, a creature whose very existence disproves the creation of god, is an example of failed adaptation. Its adaptation was so incredibly screwed up, that it has been uniquely classified by science as a "semi-aquatic mammal endemic", which in simpler terms means that it's a fish beaver duck.