First of all, as a working scientist, I have never read and will probably never read On the Origin of Species. I spend all day long reading about the latest advancements in my current field; I simply do not have the time or energy to read a historical document. When I speak of evolution, I speak of the current theory or of the biological process, not of Darwin's particular formulation of the theory, which has undergone considerable refinement.
The problem of trying to define species is that nature did not produce distinct groups of organisms that could be neatly categorized into different species. That isn't a problem of definition, it's the essence of biology.
Conveniently, such a notion, once accepted by scientists, allows a lot of leeway to finding evidence for Darwin’s ideas. If his contention is wrong, then mistaken classifications arising from it can contribute to false evidence, claiming events as “speciation”, which would not qualify under a more accurate definition. Even if the contention is correct, the ethereal standards would make it hard for scientists not to introduce bias into their classifications, and hence into their evidence for speciation.
Speciation is not an event, but a continuously on-going process. Think of how a baby becomes an adult: it is not the result of an event, but of slow change occurring over several years. There are no distinct lines between infant and toddler, toddler and child, child and adolescent, etc. Clearly, humans and finger monkeys are separate species, but if one could go far enough back in time, observing specimens every few generations, one would see the two species eventually converge until they appear to be the same.
I should also add that no one is trying to "find evidence for Darwin's ideas." Darwin used the experience of decades of personal observation, as well as the body of scientific literature from his time, to develop his theory. The theory in its modern form provides a guide for further research. The evolutionary process is a central feature of biology that cannot be ignored when trying to do research.
I’d say that’s a broad definition, because of the word “naturally”. Naturally could mean they don’t breed because of circumstances, such as geographic separation. Or it could mean that they don’t breed simply due to preference. Neither of those things gives us much useful biological information, so why should we base an important biological categorization on it? This is how we arrive at birds which are basically identical being placed in different species just because they live on different islands.
I purposefully used the word "naturally", because humans can intervene and force all kinds of breeding or hybridization that does not occur spontaneously. If you take into account cross-breeding forced by humans, then the already blurry idea of species becomes even more muddy. Factors such as geographic location or breeding preferences are quite important. When a population is split, the longer the two parts of the original population are separated, the more different they become. At some point, they become different enough to warrant being called different species.
Again, citing these as speciation events, in defense of the theory, depends on a flexible definition of species derived from the theory. We invented agriculture, and bred existing wild bovines until we wound up with the varieties of modern cow, and likewise for maize. There’s no mystery as to how these varieties differentiated from their ancestors, it was simple breeding, not evolution.
Were it not for the evolutionary forces shaping biology, no amount of breeding would have produced cows or corn. In scientific terms, natural selection describes the process by which populations change, becoming gradually more suited to their environment, and artificial selection where humans breed only those individuals with traits that benefit the humans. These are both evolutionary processes.
Well, there was the legend of the Soviet scientist who may have tried it, but there’s probably no real data. Considering the vast morphological differences and the 2 extra chromosomes, I don’t think it’s a likely scenario.
I've heard rumors of Soviet human/chimp breeding experiments, but I have no evidence that such unethical experiments ever happened. The fact that two ape chromosomes fused at some point to become one human chromosome isn't such a big deal, really. The genes are all there in either case, and our genomes are nearly identical. I can think of no biological reason that a human/chimp hybrid could not exist; what keeps us from making that hybrid is our sense of morality.
Anyway, I will have to finish this later. I must head off to work, where no doubt, I'll be spending several hours reading about the consequences of evolutionary pressures. In the area of public health, evolution is a rather big consideration.
“I simply do not have the time or energy to read a historical document.”
That’s a shame, because it gives great insight into the nature of the theory. It wasn’t until I read Origin that I began to realize just how circular the reasoning was by which Darwin supported his assertions. The theory has been refined, but it is still dependent on most of those assertions, so it’s good to examine his reasoning if you want to critically examine modern evolutionary theory.
“The problem of trying to define species is that nature did not produce distinct groups of organisms that could be neatly categorized into different species. That isn’t a problem of definition, it’s the essence of biology.”
This is essentially just repeating a tenet of evolution as fact. It’s an assumption that’s absolutely essential to evolution, so I’m not surprised that it’s usually taken as a given.
Ask yourself, though, how is that scientifically established? What experiment demonstrates that there are not distinct groups of organisms? Darwin inferred this from observation, but didn’t establish it himself, and even admitted in Origin that, if it were found not to be true, it would be very damaging to his theory.
“Speciation is not an event, but a continuously on-going process.”
Yes, of course, that’s a crucial point of the theory. However, by “speciation event” I’m talking in the context of a rapid or significant instance of the process that can be cited as dramatic evidence for the theory. If you are going to cite something as insignificant as a wild bovine becoming a domestic bovine as evidence for evolution, then you’re not providing any evidence for the more radical assertions of the theory, just the parts that everyone agrees on.
“Clearly, humans and finger monkeys are separate species, but if one could go far enough back in time, observing specimens every few generations, one would see the two species eventually converge until they appear to be the same.”
That’s a nice story, but we cannot go back in time, and nobody ever has seen such a thing, so it’s really just a fantasy. Finding a chain of skeletal remains that you can arrange in order of similarity, from monkey-like to man-like, does not establish that such a progression actually occurred as evolution predicts. Similarly, arranging genomes by similarity doesn’t establish that the similarity is due to common ancestry.
“I should also add that no one is trying to “find evidence for Darwin’s ideas.””
Well, in practice, his ideas are simply assumed to be correct, and any evidence that is found is interpreted as if those ideas were correct. So, any new or existing evidence is never critically examined to determine whether it might contraindicate the theory, but instead it is interpreted in the manner which best supports the theory. So, the result is that scientists are fitting the evidence to the theory, even if they are not consciously trying to do so. It’s simply the result of their assuming the theory to be true and hardly ever bothering to consider possible alternatives to it.
“If you take into account cross-breeding forced by humans, then the already blurry idea of species becomes even more muddy.”
Which I would cite as evidence that the idea is faulty, and should be refined in light of our experience.
“When a population is split, the longer the two parts of the original population are separated, the more different they become. At some point, they become different enough to warrant being called different species.”
At what point? This is another of the flaws of the theory. The groupings must be indistinct enough to allow for the idea of macroevolution to be tenable, yet, we observe distinct groups in nature that must be accounted for. So, there is this nebulous, undefined event where an organism undergoing gradual changes suddenly is not able to breed with its closely related organisms. Breeding is not a gradual event, it is a fairly yes/no affair, so the species cannot gradually lose the ability to interbreed.
At some point, they can interbreed, and then, they cannot. This is a “speciation event”, that really hasn’t been documented or explained by scientists. The mechanics of such an event, for sexually reproducing organisms at least, are a logistical nightmare. If a mutation causes the final change, then the first offspring of the new species is not sexually compatible with at least some of the members of the parents species. Since we don’t know exactly how the incompatibilities work, we can’t be sure that the offspring would be compatible with ANY of the parent species. If that were the case, it would simply be a dead end, an effectively sterile mutant.
Even partial sexual incompatibility is a fundamental disadvantage that isn’t taken into account in the evolutionary calculus. A beneficial adaptation that resulted in this kind of speciation would have to be advantageous enough to overcome a fundamental handicap to the essential process of the organism’s survival. Yet, that hurdle never seems to be addressed. Scientists simply pretend it isn’t there.
“These are both evolutionary processes.”
I feel like we’re talking in circles. Have you ever discussed evolution with a critic before? Nobody disputes natural selection, artificial selection, or changes resulting from recombination, or even parasitizing genes from other organisms. When critics speak of something not being evidence of evolution, we’re not speaking of them not being evidence of those processes. We are speaking of them not being evidence for what is sometimes called “macroevolution”, the part of the theory that says all organisms share common ancestry, and all species, no matter how distinct, have arisen from the gradual changes produced by the processes.
So, a wild animal changing as it is domesticated, by well understood and accepted processes, isn’t evidence for macroevolution, which is what is in dispute. Many domesticated animals and plants can still revert back to forms similar or identical to their wild progenitors, demonstrating the relatively minor variations we are introducing by these processes. The variations we introduce can seem dramatic, because we can essentially accelerate the selection process, but we’re not similarly accelerating the proposed processes necessary for macroevolution, such as mutation, so we will never see, say, a cat bred into a non-cat. It simply can’t happen by those processes.
“The fact that two ape chromosomes fused at some point to become one human chromosome isn’t such a big deal, really. The genes are all there in either case, and our genomes are nearly identical.”
We have no real definite knowledge of how much difference in the genome can exist and still allow interbreeding, so the only real test is to try it. We have many similarities in our genomes to gorillas as well as chimps, yet they can’t interbreed with each other, and I doubt either could interbreed with us. Until someone tries it, I guess it will be an open question though. I wouldn’t hold out much hope for a humanzee though :)