Genomic Information

Creationists like to claim that "information cannot increase in the genome".

The first thing to point out is that biologists rarely talk about "information" with reference to genomes. Instead, they talk about the changes to the genome, and particularly about mutations. These are classed as

1) Neutral mutations. These are changes that have no effect on the reproductive prospects of their carriers. They are the most common type of mutation, and they can build up in populations.

2) Deleterious mutations. These are the next most common type of mutation. As the name suggests, they tend to be deleted from a species' genome. This is because they have a detrimental effect on reproductive prospects, usually preventing development in the first place.

3) Advantageous mutations. The creationist equivalent is the (supposedly impossible) increase in information. Biologists class any mutation that increases the prospect of reproduction relative to the rest of the population as an advantageous mutation. Although being the rarest type of mutation, by definition, they will tend to increase in frequency in a population generation upon generation.

An important point is that these classes of mutation are with respect to the current environment. If the environment changes, a mutation can change from one class of mutation to another. The terms are meaningless without reference to the environment. Those neutral mutations that keep building up in a population can suddenly become either deleterious or advantageous.

But why is "information cannot increase" nonsense? A simple abstract thought experiment will make it clear. Let's have two variations of a section of DNA - say, GATTACA and GATTACT.

Unless they carry the same amount of "information", in a given environment, one should carry more than the other.

Let's say that GATTACA carries more than GATTACT. The latter is a mutation of the former.

Now let's have a back-mutation, turning GATTACT back into GATTACA.

This is an increase in "information"!

Now let us consider a change to the environment. Because of it, GATTACT is suddenly more advantageous than GATTACA. Which one carries more "information" now? The change has come about without either variant changing!

This is why talk of "information" in a genome is so problematic. It cannot be quantified, and taking the environment into account greatly complicates any attempt to do so. It cannot be said to increase or decrease.