Compound eyes of insects (left); mammalian eyes (right)

Convergent evolution

Evolution usually works by diversification, but sometimes a similar solution is reached by different routes

Oceans near the North and South Poles are a challenge for life. How do animals such as fish survive in temperatures around zero Celsius?

Key to survival are antifreeze proteins, which stop ice crystals forming and destroying cells. Antifreeze proteins have been seen in fish from both the Arctic and the Antarctic – but the proteins are completely different. (Read our Exploring antifreeze proteins article for more on this topic.)

Antifreeze proteins are an example of convergent evolution. An environmental challenge has been overcome in a similar way but independently in different species. Wings are another obvious example.

Building eyes

Many of the same genes are used to build eyes in both octopuses and humans.

Eyes are an interesting contrast. The compound eyes of insects and mammalian eyes are completely different, but the eyes of octopuses and mammals are startlingly similar – even though they evolved independently.

 It turns out that many of the same genes are used to build eyes in both octopuses and humans. Remarkably, many of these genes are also important in insect eye development – notably Pax-6, which seems to be a ‘master gene’ for building eyes.

This suggests that the common ancestor of all these organisms had a core set of genes involved in light detection. Over time, this core set has been added to and trimmed in the different lineages, as animals developed better ways of seeing their external world.

Lead image:

Example of an insect’s compound eye (left); mammalian eye (right).

Drosophila melanogaster adult eye: David Strutt/Wellcome Images; human eye: Kate Whiteley/Wellcome Images

References

About this resource

This resource was first published in ‘Evolution’ in January 2007 and reviewed and updated in November 2014.

Topics:
Genetics and genomics, Ecology and environment, Immunology, History, Health, infection and disease
Issue:
Evolution
Education levels:
16–19, Continuing professional development