Lethal Genes and Time Bombs

Now for a few additional definitions on top of the previous concepts.

A lethal gene is a gene that results in the death of its carrier. Genes do exist which cause diseases (such as Huntington’s disease, for example) instead of harmless changes such as blue eyes. Typically these genes kill their “host” before that host can have children, and so the gene dies with them.

Genes which kill their host but only later in life (again, Huntington’s is a good example) are called “time bomb” genes, because they wait a substantial amount of time before causing problems.

Random Variation and Natural Selection

Here we continue from the previous post introducing some useful biological concepts. As with before, these are empirically sound and don’t conflict with being anti-evolution that I can see.

Next idea: the process of copying genes (which happens when parents give a copy of their genes to their children) isn’t perfect. It’s pretty darn good, all things considered, but occasionally the chemical that comes out isn’t identical to the one that goes in.

And finally, natural selection, also known as “survival of the fittest”. This one really just makes intuitive sense; if two animals are competing for the same resource (eg food), then the one that is faster/stronger or in some other way more capable is going to get the resource. The other animal is going to go hungry, and is more likely to die.

Genes, Reproduction, and Mendelian Inheritance

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.