An Introduction to Evolution

August 13, 2008.

Evolution is not an observation nor is it any set of observations. Evolution is an explanation for a set of observations but is not those observations.

The basics of evolution:

All you need for evolution is inheritance, variation, and selection.

The variations, and their effects, can be very small. Repeat the cycle thousands of times, and the results can be dramatic.

The principles of evolution:

At its most general level, the theory of evolution states that the appearance of design and the formation of complex structures with an apparent purpose (where almost any change would make the structure fail to work) can arise without any intentional effort.

The formation occurs through a series of gradual steps. Evolution could not explain, for example, the sudden appearance of fully-formed wings on a child.

Evolution works as follows:

1.)There must be some mechanism for random changes. (For living things, this is mutation.)

2.)The things evolving must be able to reproduce by producing nearly-perfect copies of themselves.

3.)The random changes must be capable of being passed on to copies.

4.)The random changes must affect the ability of the things evolving to successfully reproduce.

And what evolution says will happen if you have these 4 things is that over time, those random changes that increase the ability to reproduce will predominate over those that don't. That is, the things evolving will, over time, become better and better at reproducing.

They will eventually appear to have been designed to successfully reproduce as they will be adapted to do so in whatever environment they evolve in.

Note that evolution does not say that those livings things that can best reproduce in fact reproduce the most. That's a tautology. It says that you preferentially carry those genes that improved the ability of your ancestors to reproduce over those that did not. And that over time random mutations that improve reproductive success will gain prevalence.

Note that in this general sense, computer simulations trivially prove that the theory of evolution is correct. However, this doesn't prove that it would happen in any case where you had just these 4 things. (And, clearly, you wouldn't. For example, if you had these 4 things, but you also had a planet where all living things were killed off every 50 years, you wouldn't evolve very much at all.) And, of course, that alone doesn't prove that the theory of evolution explains, for example, human intelligence.

Random topics.

How does evolution explain there being 2 genders?

Sexual reproduction evolved long before it had the kinds of survival value it has in primates. For example, in some primates (such as humans), sexual reproduction bonds men to women, helping to form stable relationships that protect children until they are developed enough to survive. That has obvious survival value.

The main benefit of sexual reproduction, that explains its widespread adoption by the majority of non-microscopic organisms, is the pairing of chromosomes. By inheriting chromosomes in pairs, crossover can generate new genetic combinations much more rapidly (and with less probability of producing fatal results) than mutations can.

Sexual reproduction also allows individuals with defective genes to have healthy offspring. For example, suppose I have a defective gene that is 100% fatal. With asexual reproduction, all my children would die. With sexual reproduction, half of them will live, and that half will not have the fatal gene.

Another benefit of sexual reproduction is faster selection. With sexual reproduction, good genes can become more prominent due to sexual selection. Women choose taller, healthier men, and men choose healthier women. This allows "good genes" to become more dominant in the population faster than their direct effect on survival could cause alone.

So sexual reproduction allows evolution to work faster. The rate of evolution is controlled by the rate of mutation. But faster mutations would mean more fatal mutations. So that's not a good way to speed evolution up.

But speeding up the rate at which beneficial mutations become prevalent, you don't have more fatal mutations. And you then have more opportunities to get that next benificial mutation. (Only individuals whose parents carry a gene have a chance to evolve a beneficial mutation of it.)

So it allows species to survive with a higher rate of mutation without the high number of fatalities that would otherwise cost. And it allows the same rate of mutation to create beneficial changes faster.

However, it also has a cost. Since the men can't have children, the number of child bearers is halved. As a result, some species (for example, dandelions) have ditched it where their particular circumstances made the cost outweigh the benefits.

Mutation.

Mutations do not cause evolution. They're simply one of the mechanisms by which DNA can change. You are absolutely right the vast majority of mutations have no effect whatsoever and the vast majority of mutations that have an effect have a negative effect.

However, there will still be the occasional beneficial mutation. And when that happens, natural selection will tend to favor that mutation. That is 1 component, though certainly not the only 1, of evolution.

It is possible to create computer simulations in which natural selection and random mutation alone produce creatures with progressively improved fitness. This exact technique was used to develope some of the 1st voice recognition software.