On Facebook recently, my brother asked why, if “macroevolution” is real, there aren’t more variety “in between” the species that exist today. I thought the answer to that question might be worth posting here.
The context of the question, was as comments to a tweet in which I thanked Richard Dawkins, citing his The Selfish Gene and The Ancestors Tales as having been instrumental in my scientific re-education, coming from a creationist homeschooler’s background (which my brother shares).
Among other things, all those in-between species did exist, and we’ve found scads and scads and scads of their fossiles. Most didn’t survive to today (except as fossils), because they were far less fit to compete with both descendents and cousins who were much better suited to their respective environments than today. Evolutionary jumps tend to happen when something in the environment or situation changes in a way that effects survival rates. This tends to provide strong death rates in the members that are poorly suited to deal with the change, providing a huge opportunity for members who are even just slightly better-suited to reproduce exponentially. Every small variation that is introduced that provides any sort of benefit in the new environment, reproduces quickly, because of its usefulness.
But the biggest evidence is in our genes. Every important variation introduced in a species, is genetically present in that species’ ancestors, written much the same way as in the original (minor variations obviously happen, but they bear the clear vesitages of the original genetic code). Sometimes, these features disappear, eradicated to make way for other more important features; but when these features actually disappear, and don’t transform into other ones, the genetic code for the abandoned feature still exists in the descendants’ DNA – either no longer activated to produce proteins, or subdued through variation or other genes, so that the effects they produce are just “quirks”, not particularly useful nor harmful. There are plenty of cases where retro-viruses (viruses which operate by implanting themselves in a cell’s DNA strands) were absorbed into reproductive cells, and deactivated. Those viruses are then passed on to that organism’s descendents (all in the same relative location), which adds very concrete proof that a set of species (often very diverse species) share an ancestor. Human beings, ourselves, carry such viruses as obtained from ancestors we share with chimps and other apes. It’s “garbage” DNA code, that’s inactive and has no effect, and corresponds to a known retro-virus that still exists in the wild. If it were activated, its effect would be the death of the host.
Another thing that tells us of our common heritage with the chimp, aside from the fact that 98% of our DNA is identical to that of a chimp, is that the reason we have one fewer chromosomes than chimp DNA, is that two of the chromosomes present in the chimp, are fused to form one chromosome in us. All the same basic code structure is there, but the “chromosome separation marker” got glitched into uselessness, resulting in just a single chromosome where two existed previously.
Random variation tends to be detremental far more often than progressive (usually just resulting in spontaneous abortion, or else a single organism, or a short-lived family, that doesn’t survive or reproduce well in comparison with its cousins), and even the ones that are progressive, are usually tempered with severe drawbacks that undermine survival only _slightly_ less than they improve it. This leads to a pretty volatile state, where every tiny variation that helps improve that instability even a little bit, tends to spread very quickly due to the significant improvement in survival. This tends to lead to what’s basically evolutionary “jumps” between islands of stability, because the species that were introduced in-between those islands died off much more quickly than their more-stable cousins. But we still have proof that those instable in-betweeners existed, due to a truly dizzying array of discovered fossils.
We’re a series of patches, and our biology attests to that. We have far too many flaws built into us to be the work of a perfect designer – the worst of them are simply balanced away by a large array of other patches. One big patch occurs that improves our survival (but introduces other problems), and is usually quickly followed upon by progressively smaller adjustments that help even out the problems produced by earlier “solutions”. Evolutionary jumps start out very, very ugly, but are quickly (in geological terms) smoothed out by additional “hacks” that help us function better.
Aside from Dawkins, an even more important push away from a lot of my creationist misinformation, is this Index to Creationist Claims (and rebuttals).