Wednesday, 16 November 2011

What can we learn from mutants?

Elephants with one tusk are common, but not mutants. Tarangire NP, Aug 2011
One of the joys of working in the bush is that there's always something new to see, and every now and again we come across something very, very odd. Some times we see the disfiguring effects of a disease or accident – one tusked elephants are particularly common. But occasionally we find evidence of a much more fundamental accident – a genetic mutation. One of the commonest is albanism, or partial albanism (more properly called leucisism – technically, you can't have a partial albino). True albinos are very rare in nature and occur when all the genes that control colour are, somehow, switched off (even those involved in eye-colour). I don't know if this baboon is a true albino, as I couldn't see the eyes, but I wouldn't be too surprised if he was. (I'll find out one day I'm sure – he lives in Arusha NP and I first saw him as a tiny baby over a year ago. One day he'll come close enough to see!) More often you'll see animals that lack colour in just some parts of their body, or sometimes lack all the pigments of one type – lacking melanin (which gives the black colours) is relatively common, and often results in sandy looking creatures, as the orange and yellow pigments are still present. Still rarer than colour mutations are the really strange mutants you sometimes see, like the buffalo below – something completely mad has happened here!
Albino Baboon, Arusha NP, Aug 2011

Entertaining as it is to see such strange creatures, I think there's quite a lot we can learn from these animals. Look, for example, at this buffalo, and compare it with the normal animal in the same herd – it's not doing very well! That's not surprising – with horns like that I find it very hard to believe it can graze properly – more likely ir can only nibble the tallest grass everyone else leaves, or is forced to browse, which can hardly be good for a buffalo. As for the baboon, well, he seems healthy enough – but I was still rather surprised to see him still going strong now aged one year – there are so many crowned eagles, leopards and martial eagles around Arusha National Park, and he sticks out from the crowd so much I expected him to be the first to go. He's been lucky so far... Which gives us our first lesson - most mutations are bad for the health, which explains why we don't see many more mutants when we're out and about.
Mutant buffalo (probably cow), Tarangire NP, Sep 2011

Much more normal buffalo, same herd!

So what about evolution, I hear you ask? Evolution is works because mutations are passed on from one generation to the next, yet lesson one is that mutations are bad for the health! What's going on there? Now, whilst that is definitely true for big and obvious mutations (in fact, most of the really big mutations that occur are probably automatically aborted - miscarried - in the womb before birth), it doesn't mean there aren't lots of mutations happening that we don't obviously see. In fact, for every human it's estimated that there are NNN unique mutations we have that have occurred in the genes we inherited for our parents: we don't have perfect copies of our parents DNA at all. Happily, most of the mutations have no or very little impact – which is why we don't see them – but the good news is that a few might have small benefits. And so this is lesson two, that evolution normally happens in very, very small stages – the accumulation of lots of tiny little beneficial mutations that we generally never see. That's not to say that we can't see evolution in action with the mutations we do see – in fact, the elimination of 'bad' mutations from the population is just as much a part of the evolutionary process as the incremental development of new changes. So simply by looking at this skinny buffalo, we see natural selection working – whilst the animal might still be alive (and obviously has survived a number of years), I don't think it's in any condition to pass its genes on to the next generation. So that could be my third and final lesson that we can learn from these mutant animals – that natural selection results not only in the accumulation of beneficial traits, but also in the elimination of sub-optimal genes too. That might not sound so important right away, but maybe in time we'll look at why it does matter, particularly when animal populations are reduced and individuals start to breed with their own relatives.

And finally, let's just remember that accidents – like the one-tusked elephant – are completely different from mutations. The effect of an accident will never be passed on to future generations because it's got nothing to do with genes (though the propensity to have accidents, of course, might do!). Only mutations in the DNA will be passed on to future generations, if the animal concerned survives to breed.

No comments:

Post a Comment