Homo erectus in America: this is the theme I will be posting about in my next entries. I believe that our distant and ancient relative may be a reasonable, plausible, logical explanation for several Patagonian cryptids: the giant bellicose Tirenmen and Patagonian Giants and probably the "hairy men" found in the deepest forests such as the ape men at Taitao, Chile.
With this in mind, I began reading about fossils, remains and genetic clues that may prove (or disprove) that H. erectus reached America.
H. erectus genes survive in modern humans
In 2005, Daniel Garrigan and a group of colleagues of the University of Arizona have studied a very specific region of the X chromosome* known as RRM2P4, and found that if has a great variability between humans from different parts of the world. [1]
* The X chromosome is one of the two sex chromosomes in humans (the other is the Y chromosome). Men have an X and a Y (XY), while women carry two X (XX).
To do this they sampled about 570 people, in a group that included Africans, Europeans (Dutch, Italians), Melanesians, Chinese, Japanese, and Central Asians. Their findings are surprising:
The presence of this basal lineage exclusively in Asia results in higher nucleotide diversity among non-Africans than among Africans. A global survey of a single-nucleotide polymorphism that is diagnostic for the basal, Asian lineage in 570 individuals shows that it occurs at frequencies up to 53% in south China, whereas only one of 177 surveyed Africans carries this archaic lineage. [1]
Clearly RRM2P4 is “not African”.
The cause of this difference is an ancient genetic split, and after statistical analysis, Garrigan et al concluded that all these different forms of RRM2P4 share a common “ancestor” dating back to about two million years ago.
This is roughly when our ancestor Homo erectus moved out of Africa and migrated to Asia. Additionally, the oldest form of this RRM2P4 is not African, but Asian, where it is still found.
According to Cox, H. erectus may have still been alive in Asia some 30,000 years ago, and thus could have had plenty of time to meet, intermingle (i.e. mate) with modern humans H. sapiens, and share their genes with us.
In the words of Garrigan’s team:
It is possible that the divergent, […] may be the result of recent admixture between two divergent populations; that is, the expanding anatomically modern human population and Homo erectus. [1]
No erectus, just humans
However, those that disagree, say that this is no proof of mating with H. erectus, actually the same differences between the RRM2P4 between humans could have appeared without any external intervention and that these people who have them are “outliers”, the “tips” of a normal distribution (remember statistics? Gauss’ bell?, well, there is a small but likely chance that people have unusual genes not shared by others).
Another option is that those having the “Asian” kind of RRM2P4 originated in Africa, and those that migrated to Asia survived, passing on their genes to their descendants while those left behind in Africa died out.
Both of these options were also recognized by Garrigan et al: “It is possible that the divergent, basal lineage was carried out of Africa and subsequently lost in Africa and/or increased in frequency in Asia by genetic drift.”[1].
More evidence for an Eurasian "melting pot"
A group led by Etienne Patin has looked into the The human N-acetyltransferase genes, of which two varieties exist: NAT1 and NAT2 and found evidence to support the RRM2P4 findings:
An alternative and most likely scenario to explain our data is a demographic event such as ancient population structure. A number of studies have recently reported gene genealogies that present not only unexpectedly old coalescent times (∼2 MYA) but also long basal branches [...]
Our observations at NAT1, together with these studies, further support the view that some diversity in the genome of modern humans may have persisted from a structured ancestral population [...]
In addition, NAT1*11A appears to be absent in sub-Saharan Africa, [...]
Therefore, the observation that the NAT1 gene tree is rooted in Eurasia questions the geographic location of such a structured ancestral population (Takahata et al. 2001). The origins of NAT1*11A could thus be placed either in sub-Saharan Africa, from where it must have subsequently disappeared, or in Eurasia. Should the latter be the case, the NAT1 gene tree is at odds with the commonly accepted replacement hypothesis (Lewin 1987) and is more parsimoniously explained by the occurrence of partial hybridization between modern humans expanding from Africa and preexisting hominids in Eurasia. [2]
In plain English, the gene is not found in sub-Saharan Africa so if it originated in Africa, it died out there. It is found in Asia, it is old (approx. 2 million years old - roughly the "age" of H. erectus). It is likely that modern humans received it due to "hybridization" (i.e. mating) with "preexisting hominids in Eurasia" (i.e. H. erectus).
The question is open.
I have been trying to find data on RRM2P4 in Amerindians and particularly in Patagonian natives, but have not found anything. If H. erectus had moved into America his genes would also be found there, if and when he had time to mate with humans before we exterminated them.
Lets take a look at the Patagonian's genome and see what it tells us.
Sources
[1] Daniel Garrigan, Zahra Mobasher, Tesa Severson, Jason A. Wilder and Michael F. Hammer, (2005). Evidence for Archaic Asian Ancestry on the Human X Chromosome. Molecular Biology and Evolution, Vol. 22, Issue 2, pp. 189-192. Feb. 2005.
[2] Etienne Patin et al, (2006). Deciphering the Ancient and Complex Evolutionary History of Human Arylamine N-Acetyltransferase Genes. Am J Hum Genet. 2006 March; 78(3): 423–436.
Patagonian Monsters - Cryptozoology, Myths & legends in Patagonia
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