A lot of animals have different numbers of chromosomes. An often raised objection to evolution is that this means at some point an organism would have been born with a different number of chromosomes from the rest of the population but it wouldn’t have had anything it could mate with that had the same number of chromosomes so the mutation wouldn’t have been preserved. This objection is based on the false idea that animals with different numbers of chromosomes are incapable of interbreeding.
If this was true the existence of modern domesticated horses would be something of a genetic miracle. Domestic horse populations have 64 chromosomes… wild horse populations have 66.
In reality chromosome fissions and fusions are hardly an unknown phenomenon.
One such fusion clearly occurred after the hominids branched off from the rest of the primates. Humans have 23 pairs of chromosomes, all the rest of the primates have 24. Evolutionary theory and the nested hierarchy then tells us this means there was a fusion event which reduced the number of chromosomes in humans to 23 after their ancestors split off from the wider population. If this prediction is true, we should be able to see clear evidence of it in a chromosomal analysis.
Lo and behold:
There is overwhelming evidence that human chromosome 2 is the product of the fusion of two chromosomes which just happen to look basically identical to two chromosomes found in chimpamzees… as seen in the image included in the above link.
Note that this is not just evidence that human and chimp genetic sequences kind of look the same. The telomere and centromere sequences in the middle of human chromosome 2 are clear indication that that chromosome is the product of the combination of two different pre-existing independent chromosomes. If humans had been independently created in their modern form rather than having evolved into it from a common ancestor with other animals there is no reason to expect find something like this in the human genome… but there it is.
Biogeography and Paleobiogeography
Biogeography is the mapping of spatial patterns of biodiversity. Ie: which animals and types of animals are found in which geographic regions. Combined with paleobiogeography, which is the mapping of the same in the fossil record, this presents us with yet another piece of corroborating evidence for evolution. Fossil forms which are morphologically transitional stretching back from modern animals back to earlier ones are found in geographically contiguous locations throughout the record. Obviously this is something which is to be expected if all those transitional forms were to have evolved one from the other. If they were not transitional ancestral organisms but rather just completely independent separately created lineages of some kind there would be no reason to expect the geographical distributions we do observe that they fall into.
Properties of DNA Replication
DNA is the genetic identity of an organism; it’s the primary factor in making an organism what it is biologically. The DNA changes - the organism changes.
It is a well established property of DNA that it undergoes mutation during replication on a fairly regular basis. Different nucleotides are substituted for each other, new nucleotides are inserted in or deleted from a sequence resulting in shifted reading frames, entire genes are occasionally duplicated and subsequently subjected to independent mutation events, chromosomes split and fuse… and over time those changes spread even as they continue to accumulate. There’s no avoiding that simple fact.
The genetic code of all living things is in a constant state of change and thus all living things are changing. Generation, after generation, after generation.
Another simple fact is that, unless under the influence of some restraining factor which places boundaries on the absolute range of change achievable, this fact presents us with a very simple equation:
Constant Change + Time = Greater Change.
And in dealing with the history of biological life on Earth we are considering a very, very great length of time indeed.
As for that “restraining factor”, this is one place you’ll see a great deal of anti-evolutionists try to take a stand… if you can call it that. You’ll see them say things like ”Oh sure, evolution can happen… but only microevolution that produces variation within species. Evolution doesn’t make new species.”
Of course they’re quickly forced to retreat from this claim as soon as the numerous examples of observed speciation events are called to their attention demonstrating quite unequivocally that evolution not only can but does produce new species.
The fallback position from that point is usually to say that evolution can’t produce new “kinds” of organisms. Even a cursory examination of this position topples it in short order as well. When asked to define how to recognize what a “kind” is so that this claim can be put to the test no answer ever seems to be forthcoming. When asked the nature of the genetic barrier somehow preventing genetic changes from crossing the threshold between “kinds” no answer ever seems to be forthcoming. When asked for an example of which genetic code would be preserved by this barrier they can’t describe no answer ever seems to be forthcoming. When asked on what possible other basis the claim that evolution doesn’t result in these new “kinds” is made no answer ever seems to be forthcoming. When asked how exactly a person can claim that “A” never happens when they can’t explain why it is that “A” never happens or even worse, define what “A” is in any detail whatsoever … well, just guess.
Rates of Genetic Change
Another claim you’ll see sometimes made against evolution is that there hasn’t been enough time for all the observed “microevolution” to produce the degree of biological diversity we see today. Again, a claim that is quickly debunked.
Multiple studies have been done measuring average rates of mutation within species, average genetic divergence between species, and amount of time since divergence of those species ancestral lines indicated by the fossil record in which that genetic divergence had to occur. Despite the vague claims against evolution in this respect every time an actual objective measurement is performed it somehow fails to turn up any kind of problems.
For example: the fossil record indicates the ancestors of chimps and humans diverged approximately 6 million years ago. Based on analysis of the regions of the human and chimp genomes with the highest divergences from each other today (worst case scenario from the evolutionary perspective) and using that as the basis for calculating how fast mutation would have had to occur to produce the differences between those sequences if starting from a common genome the required rate of mutation arrived at is approximately 2x10^-8 nucleotide substitutions per site per generation… taken from Futuyama’s ‘Evolutionary Biology’, Third Edition. Current measurements of the average rate of mutation of human and chimp genomes gives a figure somewhere between 1x10^-8 and 5x10^-8 nucleotide substitutions per site per generation… right where it should be.
Every way we can think of to look at the data it comes out supporting evolutionary theory. Geology... Biology and Molecular Biology... Paleontology... Genetics... every way we have of approaching this issue gives us the same answer. That evolutionary theory has it right.