Origin of Species

By Bill Baldwin

In the last few weeks I have become interested in the Neanderthal humans which occupied Europe until about 35,000 years ago (more or less). This has lead me to read several books on the subject, including The Last Neanderthal by Ian Tattersall, Extinct Humans by Ian Tattersall and Jeffery Schwartz, and The Mating Mind by Geoffrey F. Miller. Each of these spends some time talking about evolution. The Mating Mind presents the idea (which is attributed to Darwin) that evolution proceeds by preferences of mate choice as well as by "survival of the fittest." The other two handle evolution in a more general sense, talking of natural selection (which is a combination of the other two). In each of these books, as well as some others that I have read, the problem of the origin of species is discussed, and it is noted that the details of this is not well understood.

The definition of species is important here. It is given in the book The Last Neanderthal. A species is the largest grouping of individuals that can interbreed. Therefore, Homo Sapiens and Chimpanzees are different species because they cannot interbreed. This is important in determining if Neanderthals went extinct through interbreeding with Homo Sapiens, or did they go extinct through some other means. If they are a subspecies of Homo Sapiens, then the interbreeding scenario is possible. If not, then it is not possible.

Therefore, the deciding factor is when, and how, does it come to be that two groups of individuals that could interbreed suddenly (or gradually) become two groups that cannot interbreed. I will note that this is the only important point. It is not important that two species look different. They may be indistinguishable at any level. For example, a mule and a horse might look alike to an untrained eye (or one that is very nearsighted). Yet they are different species. This may be true of humanids as well. Maybe there are more than one human species that look indistinguishable, yet they may be different species. Yet as well, there may be different subspecies that look considerably different, if, for example, they are separated by considerable physical distance. For example, the subspecies of dogs are very different, but they are still the same species. A Great Dane looks much different than a cocker spaniel, but they are both dogs, and can interbreed.

There are two proposed methods of species differentiation that are I have seen presented. The first suggests that a species collects mutations – probably as recessive genes. Then, at some point for reasons that are not understood, the mutations suddenly become active, and a new species is created. Having thought about it, this seems unlikely. For example, why do different species have different numbers of chromosomes. Why do all the changes seem to occur at once (as this theory proposes)? In addition, this theory just pushes the question back. Why do the recessive genes suddenly become not recessive, which is an equally difficult question?

The second idea is that the species is divided due to a natural division, or some such. That is, the range of the species is suddenly divided by a river, for example. The two groups then proceed on their way evolving independently of each other. There is still a problem with the number of chromosomes, however. In addition, when and how do the species separate. That is, after three or four generations it is very doubtful that the species could not interbreed. At some point there would have to be an intermediate form which can breed with both the old species and the new species. Are there such intermediate forms in existence today, or have there ever been a recorded instance of such an intermediate form?

This also has a problem with aborigines. That is, the natives in Australia were separated from the people on the mainland for something like 70,000 years. Yet there was no change in species. Similarly for the Americas, although the period of separation is less.

I will offer a third explanation, which can answer the questions I've asked above. In this theory, it really doesn't matter if the species is separated from the old species by any physical object or not. The new species could form with the old species all around them. Although, I will note that it is more likely that the new species will develop in a area where the old species is somewhat thin.

The problem is that everyone who talks about the genetic mutations assume that each mutation is approximately equal. That is, a gene changes, and therefore the decedents of the individual may or may not carry the "defective" gene. The gene may or may not be allowed to win out by natural selection. This is a little overly simplistic, however.

I will divided the mutations into two general groups. The first is the group that people usually think about. That is, some feature, however large or small, is changed, and a change is introduced into the species. This is the changes that breeders take advantage of in breeding new subspecies of cows, or sheep, or whatever. Natural selection may propagate the gene, or it may eliminate the gene. However, all this is done within the species.

There is a second set of mutations, however. That is, suppose that a mutation occurred which did not just change a random feature, but rather that changed a feature that deals with the ability of an organism to reproduce. That is, a change which, whether large or small, prevents the individual from successfully interbreeding.

The treatment of the first set of mutations is well known. However, the second has not been treated to my knowledge. I will state that these second set of mutations, though rare, almost always result in a new species. That is, they will result in two groups that cannot interbreed. Either that, or the individual with this change dies, and I would say he/she/it dies as a new species that didn't make it.

I will note that this is consistent with the idea that I have seen presented in the popular press that all Homo Sapiens can trace their ancestry to a single "Eve." That is, a change in the reproductive tract resulted in a species (called Homo Sapiens) that resulted in their not being able to interbreed with the humans that were around them, even in their own clan.

There is a problem, however, that if the individual cannot interbreed with the existing species, then how can the gene be propagated? Suppose the gene were a recessive gene. Then it could be carried by a lot of individuals without being expressed. For the most part, when expressed if would result in an individual that would be said to be infertile. However, if it is common enough in the species, then it is possible that an individual who expresses this gene to mate with another individual with this trait, and the trait is viable, then this pairing could result in a new species. Over time, the new species would begin to develop independently of the main species, as if there were a barrier, even though there would be no physical barrier to separate the individuals of the species.

It would also be possible for the trait to be a dominate trait. In this case the parent would pass the gene to the children, but the the gene might not be in the cells of the parent. All the offspring (or at least half) would show the characteristic of the gene. All the members of the species at this phase would be in one family, and some form of incest would have to be used to do the initial propagation of the species. I suspect this is probably a much rarer method of generating new species, however.

If this were the case, then one would expect sudden changes from one species to a similar species, followed by long periods where the species did not change much, except possibly for subspecies, which is consistent with the fossil record. In the case where a species was divided by a natural barrier, it is quite probably that the change would be on one side of the barrier or the other, so one side would result in a new species, and the other not. However, it really would have nothing to do with the barrier. If could also happen absent any barrier.

I would note that it would be more likely if the density of the population was low because in that case the species is more likely to interbreed cousins and the like, so that the recessive gene could be expressed more often, and in closer proximity.

In addition, the fact that the offspring of the individuals that have the "defective" gene that generates the new species would have a higher likelihood of not producing offspring in the old species, the occurrence of the gene in the old species gene pool should decrease over time, and eventually be eliminated. (This might not be, however, as it may still be expressed on occasion, and we would term it as an defective recessive gene, with an occasional individual who would be sterile as far as the old species is concerned.) (How often have sterile individuals who produce sperm and eggs been checked to see if they might produce viable offspring with close relatives?)

Of course, what is generally perceived of as species differentiation would not actually happen until after the species had separated. That is, initially there might be two species which look identical, but cannot interbreed. Time and the normal evolutionary processes would result in the two species looking different after a period of time, however.

And it is reasonable that the initial genetic change may change some macro feature as well. That is, it may be possible to identify the new species immediately, and it would probably be some evolutionary changes rapidly that would allow the new species to be differentiated from the old species as if the members of the new species could not be differentiated from the old species, then the new species would attempt to breed (unsuccessfully by definition) with the old species, and the false breeding attempts could be a major problem for the new species. (Presumably the old species would be common enough that loosing a few individuals to cross breeding attempt would not kill the species.) Such false breeding attempts may be why, for examples, horses and mules may crossbreed given the proper stimulus.

The problem of the origin of species is something that has caused a problem with evolution every since the days of Darwin. I noted that two approaches have been suggested, that repressed recessive genes suddenly become activated to form the new species. Also, that a portion of a species is isolated from the main body, and goes on it evolutionary merry way until some how a new species appears. Both have problems. I have proposed a third way, which is that some genetic changes prevent interbreeding first, and after these genes express themselves to create a new species (that might actually initially look identical to the old species). Only after the new species has exists does it start to differentiate into looking significantly different than the old species using known evolutionary paths.