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Know It All: Life -- Little changes, big results

Published in Geare magazine, Issue #49, 2008

The people of the world may be divided into those who believe in evolution, and those who believe in some other explanation for the diversity of life. The people of the world may also be divided into those who think they understand Darwinian evolution and those who don't. Those who think they understand Darwinian evolution may be further divided into those who are right, and those who are wrong.

My guess is that those who are wrong is a larger group than those who are right. Especially amongst those who don't believe in evolution.

So how does evolution work?

You need just three things for evolution: replication, inheritance and variation.

Replication? Well, of course. If living creatures -- including plant life -- didn't reproduce then, in due course, there would be no creatures. But the kiddies need to be quite close copies of the parent -- or some kind of average of the parents in the case of sexually reproducing species. Otherwise, what's useful may not be preserved.

And there has to be variation. Consider, if Fred and Brian were identical in every respect, then they would presumably do just as well as each other in survival and reproduction, barring only differences in luck. Luck can't be inherited, so it can't lead to greater 'fitness'.

Once you have all three of these elements in place, and the organisms so endowed live in a world of restricted resources, then Darwinian evolution isn't merely enabled; it becomes inevitable.

Darwinian evolution -- better expressed as the theory of natural selection -- says that with variation between members of the same species, some individuals will be better than others at the all-important tasks of staying alive and producing offspring. Over time, the particular traits that aided these vital tasks are will come to be more common, simply because more kiddies are born from parents with those traits.

So what might those traits be? That depends entirely upon the environment. Because various traits are neither good nor bad when considered in isolation.

This is an important point. Natural selection is not making us, nor any other living creature, 'better'. It is not leading us towards some ultimate pinnacle of perfection. Because there is no such thing.

It is not leading us anywhere, because it has no goal. It has no intention. It is merely a mechanism, an algorithm if you like. And a very simple one at that. Take three ingredients -- reproduction, inheritance and variation -- run them through an environmental filter. Iterate over a few hundred thousand generations and you have ... well, what is it that you do have?

In the case of most mammals, you have an eye because it turns out that being able to detect and identify things at a distance is a pretty powerful survival and reproductive trait. In most cases.

But not in all cases. The ancestors of the marsupial moles of Western Australia had eyes, but the current ones don't. We know that their ancestors had eyes because the species now alive have eye lenses under the skin near where eyes would normally be.

You see, most traits come at a cost. If nothing else, the building of an eye consumes resources that could be put to better use elsewhere -- if an eye isn't of much use to you. In the case of the marsupial mole, the eye was probably worse than of no use: a positive impediment to a creature that spends just about all its time burrowing underground.

Likewise, if all carnivorous animals were banished from Africa overnight, we could expect to see the running speed of grazing animals gradually diminish over time. Natural selection would no longer 'favour' running speed for these creatures so they would develop in other directions, the better to make more and more baby grazing animals, losing speed in the process.

This would take many generations, but it would be inevitable -- until some other animal took up the carnivorous lifestyle and gave the grazers an incentive to run again.

How can we know this for sure? Maybe the lost eyes of the marsupial moles was a fluke. Maybe.

And maybe the lost eyes of the Golden Moles of southern Africa were also a fluke. These moles were for a long time believed to be closely related to Australia's marsupial moles, being of similar size, shape and lifestyle. They even share the same leather patch on the nose, which resists the wear and tear of their constant underground journey.

But these moles are not at all closely related to Australia's. The Golden moles are placental, not marsupial. They have no pouches (backwards facing in the case of marsupial moles, for obvious reasons). Their young are born much more highly developed.

Marsupial and placental mammals split from each other roughly 140 million years ago. There is no way that the two species can be closely related. Instead, doing similar things, natural selection has resulted in both species independently losing their eyes.

It is pleasing, sometimes, to think of human intelligence as the pinnacle of evolution. But it might be more useful to think of it as equivalent to the trait of a certain species of wasp, which injects into its insect victims paralysing agent, and then its larvae. The wasp's kids make themselves at home, nourishing themselves on the still-living flesh of their host.

Evolution favours what it takes to survive and reproduce. It doesn't even consider the ethics of the outcome.

© 2002-2009, Stephen Dawson