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Of Apes and Humans
by Glenda
6 February 2005
I've recently read an exchange of ideas and questions on species, humans, apes, hybrids and interbreeding. Since I'm a "layman" who never went beyond a basic biology course in college I'm right about where most of us are in our knowledge of genetics.
The exchange of ideas and clarifications in this thread were both enlightening and somewhat astonishing to me, while the implications were serious. I found new meaning in the visceral reactions many whites, those who are not brainwashed, have when they see a black/white breeding pair.
While I am not presenting this dialogue as a fleshed-out essay, I am still trying to string it along somewhat sequentially so that you, the readers, the most important and informed group in the world (you will understand what I mean by this when you read the following), can have the crux of the implications at your fingertips while also having the documentation to back up this new-found knowledge.
First I would like to give you the conclusions, and then you can read the explanations.
"H. sapiens/sapiens and H. erectus and H. neanderthalensis would have all been able to interbreed ... and the genetic evidence, given below, indicates they DID interbreed, resulting in the modern populations of today.
However, Eurasians are MORE diverged from chimps than Nigerians. Sub saharan Africans share MORE alleles with chimps than Eurasians do. That is because erectus was MUCH closer to the apes than sapiens, and Africans are derived from erectus, hybridized with sapiens, whereas Eurasians are fully sapien. This is what the afrocentrists refer to euphemistically as the Africans having 'ancestral' alleles, when they try to argue that Africans are ancestral to Eurasians, just because they are genetically more primitive."
Contributor A
Crossing the species barrier:
While most examples of cross-species hybridization produce infertile
or partially fertile offpsring, in some cases the offspring *are*
fully fertile. An example of this would be the dog family, where
even jackal-dog hybrids - once produced - are fully fertile. The more
closely related dog, wolf, and coyote species interbreed with even
less difficulty.
It is _not_ enough to say "these organisms produce fertile offspring;
thus, they are of the same species."
Biology is notorious for being a more "fuzzy" science than, say,
chemistry. Categories can be *both* real, yet indeterminate. Race
(breed), species, etc. are all real, biologically valid categories.
But where a race and species begins is not always completely clear.
Genotypic and phenotypic differences, and, importantly, differences
in niche utilization, all contribute to the classificatory process.
See http://members.aol.com/jshartwell/hybrid-mammals.html for many examples of hybrids.
Contributor B
Could humans interbreed with any of the great apes...orang-utans for example? When Europeans first encountered the great apes of sub-sahara in the 16th Century, there was a belief among some, that blacks were the offspring of such unions. Winthrop Jordan points this out in book "White Over Black" as contibuting factor to the ease with which whites were willing to enslave blacks. I think there is also a reference to this type of inter-specific breeding in Voltaire's "Candide."
Contributor A
Probably not, due to the chromosome rearrangements since their divergence. See below and www.rafonda.com .
In Number of ancestral human species: a molecular perspective, (HOMO Vol. 53/3, pp. 201ö224) D. CURNOE, and A. THORNE directly address the question of whether recent types of Homo would have been able to mate and produce viable and fertile offspring. They say, flatly:
"All fossil taxa were genetically very close to each other and likely to have been below congeneric genetic distances seen for many mammals. Our estimates of genetic divergence suggest that periods of around 2 million years are required to produce sufficient genetic distance to represent speciation. Therefore, Neanderthals and so-called H. erectus were genetically so close to contemporary H. sapiens they were unlikely to have been separate species.
Distances calculated here for H. neanderthalensis versus H. sapiens and for H. erectus versus H. sapiens are around one-third and two-thirds, respectively, of the mammalian intrageneric mode."
Some genetic data from human, chimp, and orangutans suggest there were genetic speciation events in Homo's history, resulting in populations that could not have interbred with antecedent Homo, but not many nor recently. This type of speciation, resulting in infertility by reason of genetic incompatibility, must be distinguished from the evolution of 'type' morphology, leading to species designations such as erectus and Neanderthal.
"Sumatran and Bornean orangutans differ by three chromosomal rearrangements but are known to be fully fertile, and common chimpanzees and bonobos differ by six chromosomal rearrangements, and although some workers regard them as distinct species (see above), they do produce apparently normal hybrid offspring (H. Vervaecke, pers. com.). Most types of rearrangements between orangutan subspecies and between common chimpanzees and bonobos are also seen in humans. This suggests that at least some of the rearrangements in humans might not represent reproductive isolation."
But they go on to say,
"This observation is complicated by the fact that humans appear to possess even greater chromosomal instability than great apes. Humans possess a high level of chromosomal rearrangements, with 1 out of every 120 babies born being abnormal (Hook 1992). The figure rises to about 25% for 10-day old blastocysts (Gardner & Sutherland 1996). We conclude that chromosomal rearrangements were likely to have been important during human evolution, more so than among the great apes, making comparisons with them of limited value."
And concluding,
"Given the chromosomal instability in humans, it seems likely that at least some of the chromosomal rearrangements may have had a significant impact on reproductive isolation when they occurred."
Thus, it isn't clear (from the ape evidence) that even chromosomal rearrangements would have rendered the different types of Homo infertile, but it is clear that there were fewer such events, which even might have caused reproductive isolation, than there are recognized taxons of Homo. In other words, just because erectus was different enough to be a recognized taxon doesn't mean they couldn't, and didn't, interbreed with sapiens.
The cited authors state there have been five or fewer genetic-isolation-speciations since the last common ancestor with chimps:
"From the above evidence we conclude that the number of species on the DLMH,
as inferred from human chromosome rearrangements, might be around 3 and cannot be more than 5."
So all of the types of Homo living in the last few hundred thousand years would have been fertile with the other types. H. sapiens/sapiens and H. erectus and H. neanderthalensis would have all been able to interbreed ... and the genetic evidence, as presented in the papers posted on this site, indicates they DID interbreed, resulting in the modern populations.
The drift of this is that modern humans MIGHT not have been able to interbreed with habilis; PROBABLY could not have interbred with precursors to Homo; and very likely would have been infertile with the LCA of humans and apes, let alone with their yet-more-diverged modern descendents. This is NOT to say that a chimera could not be produced by technical means.
Contributor C
This may be redundant, but is there anything suggesting that certain sub-saharan humanoids either did or did not interbreed with the apes as recently as right before the last divergence between them? (What I'm driving at is degree of "primativeness.")
Have divergences been studied separately for whites, blacks, asians?
Contributor A
Yes. You can see that the Eurasians are MORE diverged from chimps than Nigerians. IOW sub-saharan Africans share MORE alleles with chimps than Eurasians do. That is because erectus was MUCH closer to the apes than sapiens, and Africans are derived from erectus, hybridized with sapiens, whereas Eurasians are fully sapien. This cite:
HOMO Vol. 53/3, pp. 201-224
© 2003 Urban & Fischer Verlag
http://www.urbanfischer.de/journals/homo
Number of ancestral human species: a molecular perspective
D. CURNOE*, A. THORNE <
contains the following:
Nuclear DNA
Our analyses using 24 genetic distances provide an estimated speciation rate of 1-13 with a mean of 4 for all DNA distances (table 1). Some of the speciation rates in table 1 are <1. This results from the fact that some of the distances between
humans and chimpanzees, when halved, are below those between Africans and Asians.
THINK what that means: the genetic distance between humans and chimps IS LESS THAN TWICE the difference between between Africans and Asians!! And the mtDNA tells the same story:
With mtDNA:
Some of the speciation rates in table 2 are <1. This results from the fact that some of the mtDNA distances between humans and chimpanzees, when halved, are below those between orangutan subspecies, and common chimpanzees versus bonobos.
Then, this paper, using a different set of genes, finds a still-dramatic divergence between Africans and Eurasians, with the Africans having more chimp alleles. This is what the afrocentrists refer to euphemistically as the Africans having 'ancestral' alleles, when they try to argue that Africans are ancestral to Eurasians, just because they are genetically more primitive.
Population genetics of dinucleotide (dC-dA)n.(dG-dT)n polymorphisms in world populations.
Deka R, Jin L, Shriver MD, Yu LM, DeCroo S, Hundrieser J, Bunker CH, Ferrell RE, Chakraborty R.
Department of Human Genetics, University of Pittsburgh, PA 15261.
We have characterized eight dinucleotide (dC-dA)n.(dG-dT)n repeat loci located on human chromosome 13q in eight human populations and in a sample of chimpanzees. Even though there is substantial variation in allele frequencies at each locus, at a given locus the most frequent alleles are shared by all human populations. The level of heterozygosity is reduced in isolated or small populations, such as the Pehuenche Indians of Chile, the Dogrib of Canada, and the New Guinea highlanders. On the other hand, larger average heterozygosities are observed in large and cosmopolitan populations, such as the Sokoto population from Nigeria and German Caucasians. Conformity with Hardy-Weinberg equilibrium is generally observed at these loci, unless (a) a population is isolated or small or (b) the repeat motif of the locus is not perfect (e.g., D13S197). Multilocus genotype probabilities at these microsatellite loci do not show departure from the independence rule, unless the loci are closely linked. The allele size distributions at these (CA)n loci do not follow a strict single-step
stepwise-mutation model. However, this features does not compromise the ability to detect population affinities, when these loci are used simultaneously. The microsatellite loci examined here are present and, with the exception of the locus D13S197, are polymorphic in the chimpanzees, showing an overlapping distribution of allele sizes with those observed in human populations.
PMID: 7847383 [PubMed - indexed for MEDLINE]
The following is a commentary on the data in this paper, which is NOT by the paper's authors:
> One can compare the relative genetic distance between two human groups to that between those human groups and chimps, and thus calculate the former as a percentage of the latter. According to the Nei method, the German-Nigerian distance (0.238) is a full 12.8% of the German-chimp difference, while using the Cavalli-Sforza method the German-Nigerian distance (0.168) is a full 24.7% of the German-chimp distance!
Deka et al., Am. J. Human Genetics 56, pgs. 461-474, 1995. This study looks at some genetic markers and compares the genetic distances of eight human populations (Samoans, North Amerindians, South Amerindians, New Guineans, Kachari [Mongolids], Germans, more generalized Caucasians, and Sokoto Negroes from Nigeria [Nigerian sub-Saharan African Negroes]) to each other and to chimpanzees. The data were analyzed two ways - with Nei's standard genetic distance, and with modified Cavalli-Sforza distance.
Which group was genetically closest to chimpanzees? The answer for both methods was the Nigerian Negro group. Using Nei's method, the Nigerian-chimp distance was 1.334 +/- 0.375, by far the closest value (second closest was the Kachari value of 1.527 +/- 0.493). To be fair, and show we are not knee-jerk "Eurocentrics" hiding data, the group farthest from the chimps was the South Amerindians (1.901 +/- 0.529); however the Germans (1.865 +/- 0.506) and the more general Caucasians (1.860 +/- 0.497) were right behind them (and given the +/- values, virtually overlapping). Looking at the Cavalli-Sforza method, the Sokoto Nigerians were again the closest to chimps (0.539) by a large margin. The farthest were again the South Amerindians (0.712), with the Germans (0.680) and general Caucasians (0.667) being a very close third and fourth behind the South Amerindians as well as Samoans (0.711) and North Amerindians (0.697). So, while the two methods give slightly different orders, in both cases the Nigerians are by far the closest group to the chimps. Once again, given the first method, these sub-Saharan Africans were at 1.334 while all the other groups ranged from 1.527-1.901, and given the second method they were at 0.539 while the other groups ranged from 0.643 (Kachari again) to 0.712. Thus, based on these data, the sub-Saharan African group is genetically closest to chimps. ...<
The following is a list of the [human] chromosome 13q (that which was studied in the Deka et al. paper) alleles which are found in both Nigerians and chimps and NOT found in any of the other population groups studied:
FLT1 - 156 and 176
D13S118 - 184
D13S121 - 160 and 180
D13S193 - 127 and 137
D13S124 - 179
And that is all from just a study of 13q alone!
GLENDA
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