Convergent Evolution:
A Clear Explanation

Convergent evolution is a term used for the development of very similar systems or shapes in animals that have very different origins. This also applies to plants, but I'll just talk about animals in this page.

The easiest way to understand the term is to think of the first word which comes from converge, meaning to end up in the same spot. The function or forms of the two animals that have converged do not need to both be alive at the same time, though there are plenty of examples that are.

Convergent Evolution In Shapes

Ichthyosaurs, Dolphins and Sharks

Living in the open ocean as a fish eater requires a streamlined body and the ability to move very quickly when needed. These pressures caused first sharks, then ichthyosaurs and finally dolphins, to all adopt a very similar body shape and method of movement.

In all these animals the tail is the major motor, other flippers and fins are used merely for steering and the body has taken on a shape that has the least resistance to water.

Have a look at the three animals:

Thylacines and Dingoes

This is a favorite of most Australians. The Thylacine was a marsupial the same shape and size as the placental dingo. The Thylacine evolved in Australia from the same stock as quolls and native mice. It lived on the mainland as well as the island of Tasmania until the arrival of people. People brought with them dingoes, which are wild dogs.

The dingoes had the same lifestyle and diet as the Thylacines, but they had stronger jaws. Over a long time the dingoes out competed the Thylacines which wiped them out on the mainland.

Have a look at these two animals:

Convergent Evolution In Systems

The best two examples are ones we see every day and are already familiar with.

Warm Bloodedness

Being warm blooded allows animals to have a higher level of activity throughout the day and night, makes digestion far more efficient and generally speeds up all manner of chemical reactions.

Birds and mammals both share this feature. Birds have an average body temperature of 40 degrees Celsius (105 F) while mammals have a body temperature of about 37 degrees Celsius (98.6 F). Both these groups are generally far more active than the other land dwelling animal groups of reptiles and amphibians.

Flight

In vertebrates true powered flight has arisen three times from separate origins. First came the pterosaurs with their very fragile wing membranes. These membranes were from between the limb and the body, like the skin that gliding squirrels use.

Much later and from very distantly related creatures evolved the feathered dinosaurs that turned into birds. Their flight was made possible by modified scales that grew long and flat and overlapped each other.

Last on the scene were the mammalian bats. Again skin was used for the wing surface, but this time it was like the skin between your fingers. This is easiest to see between your thumb and your forefinger.

The Environment Causes Convergent Evolution

Selective pressures, combined with variation, force animals to adapt to their changing environments or perish. In all the cases given above, animals evolved in those directions as a response to their environment, one little step at a time.

They are still evolving and changing. As environmental conditions continue to change, animals will continue to adapt, and those that cannot adapt well enough will perish by being out competed by another species.

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