webbed feet
© Fcb981 / CC BY-SA 3.0, Wikimedia Commons

Written by A-Z Animals Staff

Updated: May 27, 2024

Share on:


What Is Evolution?

As with all living organisms, animals change through the generations, changes which can be difficult to see immediately but can have an enormous impact on the appearance of an animal and the way in which an animal behaves. This process of evolution often results in changes to the animal, in accordance with their surroundings and changes in their survival strategies. This process occurs very slowly over thousands and millions of years. Theories of evolution explain how different animal species are related to one another, like apes and humans for example.

Animal Adaptation

Animals adapt through a series of small, random mutations and usually do so in order to compete more effectively for food, water and space. With such strong competition between species, the animals that have certain adaptations are more likely to be stronger and therefore produce more young. Those animals with useful and favourable characteristics quickly become spread around the world, but those animals with the least favourable features tend to be pushed out as they are weaker.

Species and Speciation

An animal species is a group of animals that is able to interbreed in the same area to produce fertile offspring, in order to keep the species going. Speciation is the dividing within an animal species, producing sub-species of animals within one group. Different sub-species of animals are usually separated by a natural barrier such as water or land, and can eventually adapt to their surroundings so effectively that they become too different from their original species that the two can no longer interbreed.


Despite the sad thoughts of losing animal species, species extinction is part of the natural course of evolution, as in order for one species to survive, another species must fail. It is thought that 99% of the Earth’s animal species have become extinct since the beginning of the Earth, and that the bulk of these have happened in the last 60 million years. Today, the extinction rate of animal species is rapidly increasing due to the impact made on animals and their habitats by humans.

Species Similarities

Despite being unrelated, animal species often develop similarities which can make too completely different species of animal look very similar. This is known as convergence and makes evolutionary tracing very difficult as it can throw scientists off course. For example, dolphins which are mammals and sharks which are fish, are very similar in appearance and the two can often be confused, but they are not closely related.

Animal Partnerships

Over the millions of years that animals have existed on earth, they have formed close partnerships between one another in order to help each other survive. Animal partnerships can be as small as tiny microscopic organisms cleaning the algae from the coral, or as large as zebra and wildebeest migrating together across Africa.

Natural Selection

Natural selection is believed to be one of the most influential factors in animal evolution. Natural selection is the process where likeable or successful traits in an animal are passed along to the young in order to give them a better chance of survival. Favourable traits passed down through natural selection can be anything from changes in appearance to changes in behaviour.

Artificial Selection

Natural selection can often be difficult to spot in animals in the wild, but artificial selection (where animals are kept in a controlled environment) can make subtle changes easier to spot. Over years, animal breeders concentrate on breeding animals with favourable features, and although interesting, this can cause other problems to the animals in question. For example, a bulldog has been bred over time, to have a flattened face by using parents that have flattened faces. Initially, there doesn’t seem to be a problem but the bulldogs face becomes flatter with each generation and many today have severe issues breathing through their noses.


The constant movement of continents and changes beneath the surface of the Earth, are constantly reshaping the planet and these changes often have a dramatic effect on animal life as they split animal groups up and create completely new habitats. Animals were originally split up with the dividing of continents and the isolation of islands such as Madagascar, New Zealand and Hawaii, and are brought back together again when the land collides or with the introduction of new species to new places by humans.


Charles Darwin was a naturalist in the last century who opened up the eyes of the world, to the startling variety of life that we are surrounded by. Darwin’s ideas of the evolutionary process and natural selection were dismissed when they were first proposed and it wasn’t until the middle of the twentieth century that Darwin’s theories were actually properly studied and thought about. Darwin is most famously known for the his book called ‘On the Origin of Species’, which he published in 1859 about his ideas on evolution that were backed up by his trip to the remote Galapagos Islands.

Share this post on:
About the Author

AZ Animals is a growing team of animals experts, researchers, farmers, conservationists, writers, editors, and -- of course -- pet owners who have come together to help you better understand the animal kingdom and how we interact.

Thank you for reading! Have some feedback for us? Contact the AZ Animals editorial team.