The concept of evolution is rather controversial in certain circles, and I am not here to argue over what it means to be a “theory” or any of the other random pieces of that controversy. Instead, I intend to introduce a few core biological concepts which people associate with evolution, but which are less controversial on their own. We’ll work our way to the truth.
First concept: living beings have genes. Genes are not some magical thing; a gene is just a particular sequence of chemicals with certain characteristics. If you’ve read the blog this far you understand my position on empiricism and the scientific method. Suffice to say that the existence of genes is pretty solid given those foundations; there is trivial, indisputable evidence that these chemical chains exist in all living things.
Second concept: genes get passed on to our offspring. The mechanics of this are neat but not really interesting. In humans, each parent gives their child a copy of half their genes, so the child ends up with a full set. As with the existence of genes themselves, this isn’t really controversial; plenty of reproducible studies have demonstrated this fact.
Third concept: certain genes are correlated with certain properties in living things. For example, we have identified the particular gene that is common to most people with blue eyes (this one). The statistical evidence here is, again, overwhelming.
These three ideas together express what is typically called Mendelian Inheritance, after its discoverer Gregor Mendel. This simply states that, if your parents both have blue eyes, then there’s a pretty good chance (though not a guarantee) that you’ll end up with blue eyes yourself, since they give their genes to you. This isn’t controversial at all: red hair, blue eyes, and other similar characteristics all obviously run in families. This is why.