The modern science of biochemistry gives creationists another route to attack evolution.
It is extremely difficult for scientists to propose in detail how the structural or biochemical systems of life could change from a more simple form that was functional.
I wouldn’t say it is extremely difficult. I would say that it’s impossible. We can look at two molecules in two closely related species and see what changed, but we can never know what change occurred when.
In other words, we will never have a step-by-step path for the construction of any function. This is said with the caveat that for those structures that have appeared in the lab and that all the intermediate samples have been taken, we could reconstruct a sequence of events. But then, even Lenski’s work only takes a sample every 500 generations.
To show why this is an unreasonable expectation, I’d like any creationist to state their entire lineage from Adam and Eve (or even Noah) to present. If you cannot do this, then obviously, human reproduction is not capable of producing new humans.
Obviously that’s silly, but that is exactly what is being required by the creationists in this claim. Again, we see that creationists have built a strawman of what is required by evolution, then blasted it for not achieving that level of detail.
On the other hand, there are numerous processes which can result in an increase in complexity.
Gene duplication is a very useful (and sometimes dangerous) process. A gene duplication can occur in a variety of ways, from unequal crossing-over to genetic systems within the genome. A gene, a portion of a gene, or a group of genes is copied. For whatever reason, a daughter cell (including gametes) may contain additional copies of a gene.
As previously mention, when there are multiple copies of a gene, the one can be mutated, even severely, without affecting the production of the protein in the organism. Another, very interesting, thing that can happen is that both genes may be mutated slightly and then both are required to perform the function where only one was required before. This is a simple explanation of how evolution can create things that are ‘irreducibly complex’.
Irreducible complexity is an Intelligent Design buzz phrase. Basically the claim is that there are some things in biochemistry that are so complex that no intermediate steps would be functional. Because of that, they could not have evolved naturally and therefore must be designed.
A very simple analogy will serve to show how this is flawed. Having recently spent a lot of time watching my new home being built, I observed an example of irreducible complexity being formed. Obviously, a single wall will not stand up by itself. At least one other wall is required to support it and act as a brace against falling motion. Obviously, the roof cannot be built without all four walls in place.
By this logic, no roof can ever be built because the roof can’t be built until all four walls are built and no wall can be built until at least one other wall is present to support it. Obviously, no houses or buildings actually exist.
Instead, the framers (yes, they are intelligent, work with me here) construct temporary support braces. One set of braces hold up each wall, even when the other walls are built too. These temporary braces remain in place until the four walls are complete, the roof is complete, and the entire house is made structurally sound by exterior cladding. Once all this work is complete, then the braces can be removed and everyone is confident that the house will not fall down.
When you look at a custom built house, no one ever sees those support braces. Indeed, they disappear long before the house is finished. A careful study of the house structure may reveal indications that they existed (especially before the drywall goes up). In my house, I can show you cutouts where the braces were passing through several framed out walls. I can show you the nails that held the braces in place. But the braces themselves are long gone.
In the same way, biological systems can evolve with ‘temporary braces’ that fulfill some functions. But when other systems take over those functions, the braces are redundant and mutations that affect them are no longer dangerous to the organism. We might be looking at these temporary braces in our genome every day and not realizing that this bit of the genetic code used to be a brace that propped up our immune system until other parts started doing a better job.