Below, I have assembled a series of references and abstracts that document striking evidence for the common ancestry of humans and the great apes independently of the usual paleontological, morphological, and molecular phylogenetic data that we usually see. I first became aware of this through some postings on the internet of Clark Dorman and Don Lindsay.
When one looks at the chromosomes of humans and the living great apes (orangutan, gorilla, and chimpanzee), it is immediately apparent that there is a great deal of similarity between the number and overall appearance of the chromosomes across the four different species. Yes, there are differences (and I will be addressing these), but the overall similarity is striking. The four species have a similar number of chromosomes, with the apes all having 24 pairs, and humans having 23 pairs. References 1 and 2 each contain high resolution photomicrographs and diagrams showing the similarity of the chromosomes between the four species (ref. 1 only covers humans and chimpanzees, ref. 2 covers all 4 species). Furthermore, these diagrams show the similarity of the chromosomes in that every one of 1,000 nonheterochromatic G-bands has been accounted for in the four species. That means that each non-heterochromatic band has been located in each species. (I hope to add a scan of the full sets of chromosomes for all four species in the very near future. In the meantime I'll have to make do with a couple of examples of the most rearranged chromosomes that Don Lindsay has posted.)
Creationists will be quick to point out that despite the similarities, there are differences in the chromosomal banding patterns and the number of chromosomes. Furthermore, they will claim that the similarities are due to a common designer rather than common ancestry. Let's address the differences first, and then we will see if we can tease apart the conflicting scenarios of common ancestry vs. a common designer.
The following observations can be made about similarities and differences among the four species. Except for differences in non genetic heterochromatin, chromosomes 6, 13, 19, 21, 22, and X have identical banding patterns in all four species. Chromosomes 3, 11, 14, 15, 18, 20, and Y look the same in three of the four species (those three being gorilla, chimps, and humans), and chromosomes 1, 2p, 2q, 5, 7 - 10, 12, and 16 are alike in two species. Chromosomes 4 and 17 are different among all 4 species.
Most of the chromosomal differences among the four species involve inversions - localities on the chromosome that have been inverted, or swapped end for end. This is a relatively common occurrence among many species, and has been documented in humans (Ref. 8 ). An inversion usually does not reduce fertility, as in the case I have referenced. Don Lindsay provides a diagram of the chromosome 5 inversion between chimpanzees and humans scanned from ref. 1. Note how all of the bands between the two chromosomes will line up perfectly if you flip the middle piece of either of the two chromosomes between the p14.I and q14.I marks. The similarity of the marks will include a match for position, number, and intensity (depth of staining). Similar rearrangements to this can explain all of the approximately 1000 non-heterochromatic bands observed among each of the four species for these three properties (band position, number, and intensity).
Other types of rearrangements include a few translocations (parts swapped among the chromosomes), and the presence or absence of nucleolar organizers. All of these differences are described in ref. 2 and can be observed to be occurring in modern populations.
The biggest single chromosomal rearrangement among the four species is the unique number of chromosomes (23 pairs) found in humans as opposed to the apes (24 pairs). Examining this difference will allow us to see some of the differences expected between common ancestry as opposed to a common designer and address the second creationist objection listed above.
There are two potential naturalistic explanations for the difference in chromosome numbers - either a fusion of two separate chromosomes occurred in the human line, or a fission of a chromosome occurred among the apes. The evidence favors a fusion event in the human line. One could imagine that the fusion is only an apparent artifact of the work of a designer or the work of nature (due to common ancestry). The common ancestry scenario presents two predictions. Since the chromosomes were apparently joined end to end, and the ends of chromosomes (called the telomere ) have a distinctive structure from the rest of the chromosome, there may be evidence of this structure in the middle of human chromosome 2 where the fusion apparently occurred. Also, since both of the chromosomes that hypothetically were fused had a centromere (the distinctive central part of the chromosome), we should see some evidence of two centromeres.
Human Chromosome 2 and its analogs in the apes - from Yunis, J. J., Prakash, O., The origin of man: a chromosomal pictorial legacy. Science, Vol 215, 19 March 1982, pp. 1525 - 1530
The first prediction (evidence of a telomere at the fusion point) is shown to be true in reference 3 . Telomeres in humans have been shown to consist of head to tail repeats of the bases 5'TTAGGG running toward the end of the chromosome. Furthermore, there is a characteristic pattern of the base pairs in what is called the pre-telomeric region, the region just before the telomere. When the vicinity of chromosome 2 where the fusion is expected to occur (based on comparison to chimp chromosomes 2p and 2q) is examined, we see first sequences that are characteristic of the pre-telomeric region, then a section of telomeric sequences, and then another section of pre-telomeric sequences. Furthermore, in the telomeric section, it is observed that there is a point where instead of being arranged head to tail, the telomeric repeats suddenly reverse direction - becoming (CCCTAA)3' instead of 5'(TTAGGG), and the second pre-telomeric section is also the reverse of the first telomeric section. This pattern is precisely as predicted by a telomere to telomere fusion of the chimpanzee (ancestor) 2p and 2q chromosomes, and in precisely the expected location. Note that the CCCTAA sequence is the reversed complement of TTAGGG (C pairs with G, and T pairs with A).
The second prediction - remnants of the 2p and 2q centromeres is documented in reference 4. The normal centromere found on human chromosome 2 lines up with the 2p chimp chromosome, and the remnants of the 2q chromosome is found at the expected location based upon the banding pattern.
Some may raise the objection that if the fusion was a naturalistic event, how could the first human ancestor with the fusion have successfully reproduced? We have all heard that the horse and the donkey produce an infertile mule in crossing because of a different number of chromosomes in the two species. Well, apparently there is more to the story than we are usually told, because variations in chromosome number are known to occur in many different animal species, and although they sometimes seem to lead to reduced fertility, this is often not the case. Refs 5, 6, and 7 document both the existence of such chromosomal number differences and the fact that differences do not always result in reduced fertility. I can provide many more similar references if required. The last remaining species of wild horse, Przewalski's (sha-val-skis) Wild Horse has 66 chromosomes while the domesticated horse has 64 chromosomes. Despite this difference in chromosome number, Przewalski's Wild Horse and the domesticated horse can be crossed and do produce fertile offspring (see reference 9).
Now, the question has to be asked - if the similarities of the chromosomes are due only to common design rather than common ancestry, why are the remnants of a telomere and centromere (that should never have existed) found at exactly the positions predicted by a naturalistic fusion of the chimp ancestor chromosomes 2p and 2q?
Another chromosomal rearrangement has recently been discovered, this one shared both by humans and chimpanzees, but not found in any of the other monkeys or apes that were tested. This rearrangement was the movement of about 100,000 DNA pairs from human chromosome 1 to the Y chromosome10. See "The Promise of Comparative Genomics in Mammals" Science, Oct. 1999 to learn how similar chromosomal comparisons are being used to map the evolutionary relationships of all living mammals.
Please e-mail questions, suggestions, or comments to Robert Williams
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1. Yunis, J. J., Sawyer, J.R., Dunham, K., The striking resemblance of high-resolution g-banded chromosomes of man and chimpanzee. Science, Vol. 208, 6 June 1980, pp. 1145 - 1148