Science, Just Science

What Is Evolution?

What Is Evolution?

It seems a strange question to ask. But evolution is often misunderstood, even in the scientific community. It is this very lack of understanding that the ID movement uses – the ID tactic is to redefine parts of evolution in a different way, and then set about attacking these redefined bits. But is what they are attacking actually evolution, or not?

Definition Of Evolution

So, this post will define what evolution is. It will also list quite a few things that evolution is not – just for the benefit of the ID proponents. The introduction to evolutionary biology at talkorigins is a very good primer for evolution.

Quote from talkorigins:
“Evolution is a change in the gene pool of a population over time. A gene is a hereditary unit that can be passed on unaltered for many generations. The gene pool is the set of all genes in a species or population.”

And that, ladies and gentlemen, is it. That is the definition of evolution.

Where the misunderstanding starts is when people start confusing (among other things) some of the mechanisms behind evolution with evolution itself.

Natural selection is not evolution

Natural selection is one of the mechanisms suggested by Darwin. Is natural selection the same as evolution? No it is not. Natural selection is defined as the “differential reproductive success of pre-existing classes of genetic variants in the gene pool”. Sounds a bit of a mouthful, but in fact it’s fairly simple. Genes do change, by a number of different mechansims (see later). Usually, a change in a gene will be bad – it will often cause an early death for the organism, or make it less likely to reproduce. Very, very occasionally, a change in a gene will be good – i.e. the change will give the organism a better chance of reproducing in the current environment that other organisms in the same species.

This difference in ‘reproductive success’ is called natural selection. Natural selection works alongside chance and the size of the population as well – even beneficial changes can fail to be spread by chance (early death through predation for example), and also beneficial changes may take a long time to spread through a large population (many generations).

So while natural selection is part of evolution – it’s one of the mechanisms behind evolution – it is only a part. It’s not the same thing as evolution, and there are other mechansims, including other forms of selection, that are also a part of evolution.

Common descent is not evolution

Is Darwin’s theory of common descent the same as evolution? Common descent is the scientific theory (one very well supported by the evidence) that all organisms are linked via descent to a common ancestor. So evolution can be said to be the enabling force behind common descent – we all started from one place, and got where we are today via evolution.

Does evolution represent progress? Do we automatically evolve from ‘lower’ life forms to ‘higher’ life forms? No. Populations simply adapt to their current surroundings. They do not necessarily become better in any absolute sense over time. A trait or strategy that is successful at one time may be unsuccessful at another. Much as members of the species homo sapiens would like to believe that they are the ‘pinnacle’ of evolution on this planet, they are not. There is no such thing.

So – why has more complex life evolved? Because it gives good reproductive success. Simple as that. It may not even be as good as the reproductive success of very simple life forms such as bacteria, but it’s good enough to have been maintained.

So is common descent the same thing as evolution? No. It’s one of the predicted and observed effects of evolution.

Abiogenesis is not evolution

Pretty much ever since the discovery of the structure of DNA, scientists have been wondering how it could have formed in the first place – in other words how life on earth began. There are a number of different hypotheses about where DNA could have come from and how it could have formed. As these hypotheses are not backed up by any evidence at the moment, and have not been recreated in the lab, they have to remain as speculation.

The investigation into the origins of life and DNA are called abiogenesis. Is abiogenesis the same thing as evolution? No. It’s related to evolution in that concerns DNA, which is what genes are made of. Note that evolution doesn’t require to know where DNA came from – remember that evolution is simply the change in the gene pool of a population over time. ID proponents will often say ‘evolution can’t show where DNA comes from’. Well evolution doesn’t say anything about that. Abiogenesis does.

Finally…

I hope this little essay helps to clear up some of the common confusions about evolution. It’s very important when discussing evolution that the correct terms are used in the correct context, and it’s a common tactic of evolution ‘opponents’ to deliberately confuse the context.

A lovely analogy I came across – I can’t remember where this is from sorry – but it goes like this: “An opponent of evolution saying to a biological scientist that he doesn’t believe in it – is like somebody sitting in an airport surrounded by both flying and parked aircraft saying to some aerodynamic engineers ‘I don’t believe anything heavier than air can fly’. Evolution is all around us – those that work with it see it every single day.” So true…

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