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Jimmy on the Evolution Megalab

Updated Tuesday, 24th February 2009

How can a common snail, found in parks and gardens everywhere, show evolution in progress - and help track climate change? Jimmy Doherty explains.

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There is growing evidence of climate change all around us: milder winters, spring flowers blooming earlier and extreme weather events that seem to be becoming more common. Will animals and plants evolve to cope with this changing world?

As part of the celebrations to mark Charles Darwin’s 200th birthday this year, we’re going to do a huge evolutionary experiment called the Evolution Megalab to find out. Join in and you could see evolution at work in your own back garden or in the local park.

If you visit, you can find out all about the Evolution Megalab. This is an audio guide to help you along.

OK, so evolution is a very slow process. Life on Earth started about three-and-a-half billion years ago! It's the tiny changes accumulating over a long, long time that got us here. And you can see some of those tiny steps by helping out with the Evolution Megalab. We’re going to hunt for the banded snail.

Its very common and you can find it anywhere in Britain that snails are generally found. What’s special about the banded snail is that it comes in assorted colours. Their shells are various shades from yellow through pink to brown. They can have one band round the middle like a karate black belt, five bands like a teeshirt or even no band at all.

These differences between individual banded snails are inherited, so its like banded snails are crawling around wearing teeshirts that tell us what’s in their genes.

All this talk of teeshirts and genes may make it sound like banded snails are dressed-to-kill, but the truth is they are dressed not to be killed. Banded snails are a favourite food of the song thrush and their various shell colours and patterns are camouflage.

But, why do different snails have different camouflage? We think the answer is the same reason the army has different colours for its battledress in different countries. The colour of the background is different in different places.

Experiments done by scientists over the years have shown that birds hunt by sight, not by smell as mammals do. In grass, thrushes find it harder to spot snails that have bands and yellow shells, so natural selection favours snails with genes for these characteristics. In woods and under hedges, the background is darker and yellow shells and striped shells are more conspicuous. Here, predation by birds favours darker, pink or brown colours and unbanded shells.

So that’s the first thing you can do. Go out and hunt banded snails in different places and tell us what you have found. Visit for details and a link to the Evolution Megalab where you can share your observations with us.

Thrushes aren’t as common in England as once they were, so we especially want your help to find out whether the link between shell colour, banding patterns and type of habitat that scientists have found in the past is still there. Its possible that the snails have evolved in response to a change in the numbers of thrushes that feed on them.

If you live in Scotland, or anywhere else where thrushes are still plentiful, we can use your observations as a control, like a benchmark, for any evolution that might have happened in England. So, we want your observations too! But there is another reason why everyone’s observations are important as well. It’s to do with climate.

Where does climate come in to all this? Well, it turns out that climate also influences shell colour and banding patterns. Snails are ‘cold-blooded’ little creatures that depend upon warmth from their environment to get them up to a temperature where they are able to do what a snail's gotta do: eat plants and make more snails.

Of course its colder in the north of Britain than in the south, so this means that snails in the north have less time during the year (and during the day) when they are warm enough to be active. This is where evolution kicks in.

Banded snails with darker shells and more bands (which are dark) warm up more quickly than lighter coloured and unbanded snails, so the former have a particular advantage over the latter in a cold climate. Sure enough, studies of the banded snail have found that darker and more heaviliy banded snails are more common the further north you go in Britain.

But, our climate has warmed up in the decades since some of these studies were done. In fact, it’s on average about half a degree warmer now than it was 50 years ago in Britain.

This may not sound like a big change, but it has added weeks to the period of the year when plants can grow and snails can be active. Has this change in climate shifted the frequency of banded snails with darker shells? We don’t know, but you can help us find out!Visit now and join in with the Evolution Megalab!

Take it further

Find out more, get involved, and share your results at the Evolution Megalab.

  • Editor's note: In this piece, Jimmy mentions was, until 2011, the website for programmes co-produced by the BBC and The Open University. All its content, and its spirit, can now be found here on OpenLearn.




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