What is Evolution?
There are many misunderstandings about evolution. Let’s make sure we know what it is before covering some misunderstandings.
What is evolution? Wikipedia defines evolution as:
[The] change in the heritable characteristics of biological populations over successive generations.
What does this mean? What are heritable characteristics?
Heritable characteristics are the characteristics of an organism that are passed on from generation to generation by means of an organism’s genes.
When an organism receives its genes from its parents, it will not receive perfect copies of these genes. Its genes will be slightly different than the genes it inherits from its parents. It will have its own unique mutations.
There are many possible reasons why an organism’s genes may change. But, in any case, it is these gene mutations which lead to changes in heritable traits, which can spread through populations.
This is assuming that species reproduce sexually. Some species reproduce asexually and make copies of themselves. Here we are talking about sexual reproduction. But, evolution of asexual species also occurs by gene mutations.
When these changes in heritable characteristics spread throughout a population, then evolution has occurred. In other words, evolution is the widespread change in the characteristics of a population caused by genetic variations.
The key word here is population. Evolution is not about genetic changes in individuals. It refers to changes that are widespread among individuals in a population. And not simply changes experienced by an isolated individual.
What might an example of evolution be?
Take a population of finches. Suppose some of them undergo genetic changes. And these changes mean that those finches have beaks more suitable for eating the food available in its environment. They pass the genes for this better beak to their offspring.
Those offspring pass their genes to their own offspring. Eventually, the other finches in the population will have inherited genes for this better beak.
As we shall see in the second part of this series, we have seen such examples of evolution happen. Within very short periods of time!
These are beneficial changes. Which increase the chances of survival. These are the mutations which tend to be more likely to be passed on. Ones that increase the chances of surviving to breed. And are thus more likely to be passed on and to spread among populations.
But not all evolutionary changes are good. Some are neutral and have no real effect either way. They are passed on and spread through a population anyway.
Evolution is simply the accumulation of changes in heritable characteristics in a population. Nothing about that says that those changes must be beneficial to the species. Or that they cannot be harmful.
However, beneficial changes mean that the affected organisms are more likely to survive and pass down these genetic changes. Which means that beneficial changes are more likely to spread throughout the population.
Is evolution the same as speciation? No. Speciation is the process by which new species arise as a result of an accumulation of evolutionary changes.
Speciation occurs when a population has accumulated sufficient genetic changes that it can no longer breed with populations of its parent species.
At this point they have branched off into their own species and speciation has occurred. This typically happens as a result of populations becoming geographically isolated.
Evolution is the process by which speciation occurs. But it is not the same thing as speciation. Which is simply one result of the accumulation of evolutionary changes under certain conditions.
Natural selection is not the only known means by which evolution occurs. No. It was the mechanism Darwin proposed in the Origin of Species.
We now know that there are several other important mechanisms by which evolution occurs. Other methods include genetic drift, genetic hitchhiking and gene flow.
We are not here to discuss how evolution happens. That is a very complicated topic which could take up another article or several. Today we will simply provide evidence that evolution does happen.
Now that we have some idea of what evolution is and what it is not, is there any evidence for evolution?
Yes! There is an abundance of extremely compelling evidence for evolution. So much that it would be absurd to contend that it is not proven far beyond any reasonable doubt.
The evidence is so good that it would be absurd to contend that evolution did not happen. It would be about as absurd as if someone alleged that gravity does not exist!
The evidence is diverse. Many areas of biology have an amazing gluttony of evidence! Practically every major branch of biology contains lots of evidence for it!
We will look at evidence from a few sub-fields of biology and find some truly remarkable further evidence.
What are these fields? Here are some of them.