Wednesday, May 11, 2005

A (Very) Brief Overview Of Evolution

Since there seem to many misconceptions about what evolutionary theory is or is not, and what has and has not been found so far, I feel like now is the time to explain it. There are more complete explanations than mine, but this is meant as an overview to answer some of the misconceptions.

First, evolution refers to change over time, generally millions of years to speciate (evolve from one species to another genetically incompatible species). Start in your head with one species spread out over a large area. In any population, selection pressure is present for more desirable genetic traits, in humans too, but when times are good and most of the population is able to reproduce, there is little reason for small differences caused by mutations to become the norm in the gene pool. The mutations are just folded into the normal population and you can have all kinds of variance. For long periods, there will be no evolutionary reason to change. Then there will be a physical barrier that will impede the exchange of genes across the entire population. We see this sort of thing all over the world today. Marsupials are almost entirely confined to Australia for instance. They happened to go in that evolutionary direction based on pressures found on that continent, whereas elsewhere it did not happen. The barrier can also be distance. If the range for a species is extremely wide, the same effect can occur.

Then, disaster strikes, as it does with regularity on Earth. An asteroid hits, the climate changes, a new predator moves in, or any number of other calamities, and the existing species or portion of a species must adapt or die out. Suddenly, the little differences aren't so little any more for at least one part of the population. The longer-legged creatures will run faster, and predators will eat the shorter-legged ones instead. The climate gets colder and suddenly longer fur is a real life-saving asset. Genes that were once scattered in the population are now heavily selected for, and the look and genetic makeup of the species can change quickly and dramatically. If there are enough genetic differences in the population over a long enough time, genes between the two of them become significantly different in length or structure. Fertility between the "old" and "new" forms suffers, and eventually they are so different that fertilization is impossible. We see the early stages of this in modern day horses and donkeys. They are similar enough to breed, but not enough to produce fertile offspring. There are other examples especially in birds where there are similar phenomena. Lions and tigers can breed, but the fertility rate is not the same as with the original species. We can see these various stages of speciation.

Speciation can result in many different outcomes based on what fossil evidence and genetic analysis tells us. Parts of the population could die out, leaving another part under different pressures unchanged. Two different species could result from one. One different species plus the original species could remain. The entire species could evolve into another. The whole species could die out and not be replaced. All of these scenarios can occur.

One logical fallacy that is often presented is that it is impossible to reproduce speciation in a lab environment. Yes, it is true that we do not yet have either a time travel machine or a time speeding machine where we can see what happens over millions of years in a bottle. We see all of the necessary phenomena that I have outlined in various stages of action, in the lab and in nature, but in terms of evolution, humans have only existed for about the blink of an eye, and you are asking for us to reproduce millions of years in a few decades. We aren't completely there yet, but it does not mean that it's "impossible". All of the individual building blocks necessary are there for speciation to happen, and observable. We just can't speed up time.

Another fallacy also presented is that there are no "missing links". Due to the selection pressures necessary to cause speciation, the "transition" period is pretty quick geologically speaking, about what would be expected from a quick extinction or adaptation to a (relatively) sudden change. The environment is generally similar for a long time, and a sudden shift makes the process accelerate. Without genetic material or any soft tissue at all for that matter, it is very difficult to prove beyond a doubt that something is a transitional form, but we do find these forms on a regular basis. Certainly for humans in this case we have more evidence than for many other animals. Cro-magnon man, Neanderthals, and other types all made an appearance, leading to where we are today. Cro-Magnon man especially were actually quite similar to us. Neanderthals quite a bit similar as well, but probably not enough to reproduce with modern humans. Even just yesterday another portion of a "missing link" was found.



This brings up the issue of "halves are useless". Evolutionary cul-de-sacs are everywhere. We still have an appendix. Ostriches still have wings. So do kiwi birds. Bulls don't need horns in order to survive any more, since they are domestic, but it doesn't mean they disappear. They are not selected against, so they continue. The eye is a frequently used example in the opposite direction. What good is half an eye? Not much. However, each form comes from the last form, so of course the more "advanced" form is heavily selected for, and the old form dies out. If the change is not a good one, it won't last long. People that throw out analogies like a watch randomly coming together from nothing are posing the question as if that is what evolution is. It is not. It goes from one functioning unit to the next. Those that do not function are selected against.

There is much, much more to this, and far more detail than I could possibly put in one post, but at least this is an overview. Post some of your objections if you would like and I would be happy to answer as best I can.

Update: Nicnerd IMed me from his conference and told me there were "truck-sized" holes in my post, and mentioned that there are shell fossils in the Himalayas. Interestingly, that particular fact is something touted by "Young Earth" proponents, which Nicnerd is not. I'm not sure where he got that info. His fact is correct. The Himalayas were formed around 25 million years ago when continental drift shoved the Indian plate into the Asian plate. The land portion of both of these plates were underwater at one time, when "shells ruled the Earth". This was from around 300 to around 450 million years ago, roughly. Shells in the Himalayas? We should expect nothing less!

4 comments:

Erik Grow said...

1. Reproducing speciation has not yet fully been done. It does not mean impossible by any stretch. Evolution as a whole is not immutable at all, but nearly every basic component that facilitates it is provable.

2. How would you evaluate the current data differently?

3. You are quite correct on that. There are numerous examples among dinosaurs and other species that are not able to adapt quickly enough, or as you say simply do not have enough of the necessary characteristics in the gene pool to make it. Species die out all the time. Evolutionary cul-de-sacs occur all the time, or there could be rodents the size of bears grazing in your backyard instead of woodchucks. ;-)

4. Hmmm, so you are saying since evidence can be interpreted as both, that it supports both. You are partly right. The basic problem with ID however is that it is also impossible to DISprove. Everything could be seen as evidence for it, because it is impossible for there to be evidence against it. In order for science to be tested, there has to be some kind of true/false test available of some aspect of it. What evidence could anyone ever produce in order to disprove ID? Even if I could prove that speciation definitely happens now, which we see abundant signs pointing to, but no time machine to prove beyond a shadow of a doubt, that still doesn't prove that is how we got here. This makes it faith-based and dependent on divine intervention, which makes it not science. It doesn't make it automatically wrong, but it is why it does not belong in school.

There are any number of different ways that evolution *could* be discredited. You could prove natural selection doesn't happen. You could prove mutations and natural transpositions of genetic material don't account for enough change to speciate. You could prove that all animals lived at the same time once.

Erik Grow said...

1. God existing or not has nothing to do with evolution.

2. Evolutionary theory has a great deal more of the pieces than you seem to think. All of the individual pieces necessary are very much observable and testable. You refer to it as a "theory in crisis", but I have not heard of any evidence that has refuted any of the research I have talked about here. If you want to believe ID as an alternative, that's fine. Nobody says you have to believe anything is correct, no matter how much evidence is behind it. I'm still waiting for research for ID or against evolution.

3. This is not necessary at all for evolution. All intermediate stages are viable. You are essentially saying that your mind would be eased if evolution were to explain something that it does not require. Your statement indicates that you don't understand evolution very well, no offense meant.

4. This is another common objection to evolution, one that nicnerd and others I think share as well. It is however, not an obstacle, and I can explain why. You are thinking of it in terms of the way things are today being the only or the optimum way that they should be. There are numerous other directions that evolution can take things to overcome the same problem. Longer fur, migration, hibernation, larger size, and more are all solutions to the problem of cold climates. Whichever viable option surfaces in the population first will eventually be dominant. You are also again thinking of things in terms of there never being a pre-cursor to the complex structures that you see in the world. There is also no set order as you are hinting. You are only seeing what HAS happened, not the hundreds of different ways that things COULD have happened.

Erik Grow said...

Certainly that makes sense to teach the whole thing, what we know, and what is still not known.

I do not advocate holding up the current model of evolution as the only and ultimate truth, but it certainly has the most evidence so far.

Erik Grow said...

The problem as I mentioned for much of this is the problem of time. There just isn't enough time to prove beyond a shadow of a doubt, at least so far. Nobody can force anyone to believe anything else. On to a new topic, once I decide which one to write on.