What is Evolution?
There are many misunderstandings about evolution. Let’s make sure we know what it is.
descent with modification from preexisting species : cumulative inherited change in a population of organisms through time leading to the appearance of new forms : the process by which new species or populations of living things develop from preexisting forms through successive generations
Evolution is a change in heritable characteristics which leads to new species of organisms arising out of the populations of other organisms.
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 from the genes it inherits from its parents. It will have its 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.
The keyword 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.
Some apes developed characteristics that made them increasingly more human and then their descendants developed more traits that made them more human.
Over time, some apes developed shorter arms. This turned out to be an advantage, so their descendants tended to have shorter arms. Until all the apes descended from those apes had shorter arms.
At some point, their descendants started developing larger brains. This was an advantage and over time all their descendants had larger brains.
And then they started developing mouths and skulls more adapted to being able to talk. This was an advantage and over time, all their descendants had most of these features and their mouths and skulls were more suitable for talking.
And so on. Over time their descendants developed more and more features of humans and started to look and act more and more like humans. Then, eventually, the descendants of those monkeys had every feature of a human and must therefore be classified as humans.
That is what evolution is. Changes in heritable characteristics that accumulate over time. Until you have a population of descendant organisms that are a different species. That is, they are unable to breed with the original species. They have accumulated a bunch of changes in features that justify classifying them as a subgroup of the parent group.
Evolution is groups of beings accumulating enough changes to be classified under sub-categories of the original group. Members of one group accumulate changes in features, until they are sufficiently distinct from the parent group to be classified as something that their ancestors were not.
This is how dinosaurs gave rise to birds. Some dinosaurs developed features that qualify them as birds. The newer dinosaurs are birds because they met the criteria for classifying as birds, but their ancestors do not possess all the features required to be classified as a bird.
It is the same with humans from the other mammals. Humans are mammals and at some point, our ancestors were mammals but did not qualify as humans as they did not have all the features required to be classified as human.
But over time our ancestors took on more and more of those features until they met every classifying feature of a human. And then humans existed.
Again, this what evolution is. Organisms belonging to one group of organisms change features until they qualify as members of a subgroup of organisms that their ancestors did not belong to.
What is an example of evolution we can see in our lifetime? Here is one.
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.
These changes may accumulate so that eventually the offspring of these finches are sufficiently distinct from their ancestors as to qualify as members of a different species.
This has been observed to happen in a few decades! On multiple occasions.
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!
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.