Research combining evolution and developmental biology – ‘evo-devo’ – has become increasingly popular


Dolphins have almost entirely lost their rear limbs.


Ulises Sepúlveda Déniz/iStockphoto

Evolutionary perspectives can shed light on the millions of years of change that have led to the current forms of familiar animals, including humans.

Many amphibians, reptiles, birds and mammals are four-limbed ‘tetrapods’. (They generally have four legs, or two legs and two wings, or two legs and two arms, as in our case.) Because tetrapods evolved from a common ancestor, they all have the same basic bone structure in their limbs – the pentadactyl limb, which has five digits. Your hands and feet are good examples. Even horses, which now only have one toe, originally had five, and they still carry the genetic programme for making that many – it’s just not switched on in the developing embryo.

Whales and dolphins, by contrast, are mammals that have almost entirely lost their rear limbs. By looking at whale and dolphin fossil records to see how limbs have changed, and analysing the activity of genes involved in limb formation in those alive today, a US group has suggested that gradual loss of activity in a gene known as ‘Sonic hedgehog’ has led to a reduction in limb size, starting around 41 million years ago.


Further reading

About this resource

This resource was first published in ‘How We Look’ in June 2008 and reviewed and updated in November 2014.

Physiology, Ecology and environment, Genetics and genomics, History
How We Look
Education levels:
16–19, Continuing professional development