age and origin of the human species - human origins

8/13/2019 Age and Origin of the Human Species - Human Origins

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Age and Origin of the Human Species

The speciation event that produced Homosapiens sapienscould not have occurredcontemporaneously in more than a very few individuals. It follows that those few s. sapienswould havepossessed a very restricted sample of the progenitor species' genetic diversity. However, the diversityobserved in current populations implies that there were never less than several thousand breeding pairs in

the human ancestry (Harpending et al., 199!. "ccordingly, the founding s. sapiensand their descendantsmust have interbred with the progenitor species (and perhaps other pre#human populations! in order to

preserve the diversity which e$ists today.

%hile some changes in the genome must have occurred after the speciation event, the &lifetimes& ofthe genetic elements considered (in this conte$t and the wors cited here! are far longer than newestimates of s. sapiens' age (ountain et al.,199)!. "s a conse*uence, most current diversity must be theresult of interbreeding with pre#human populations. +n this view we would e$pect to see the mosthybridied elements of the modern indigenes in those areas where pre#human population density washighest, such as "frica and -. . "sia. "lso, we would e$pect those populations to have the greatestdiversity today, because they would preserve more of the pre#human genome, which would have had

much more genetic variety than was represented in the tiny, original population of s. sapiens.

In fact, we do find that "fricans and some -. . "sian populations have not only more diversity

(/orde et al., 1990!, but central "fricans are said to have ancestral genetic elements as well (Tishoff et

al., 199!. It is also clear that the population which gave rise to s. sapienshad been separated from thesub#-aharan "fricans' ancestors for longer than our species' lifetime.1This re*uires the proponents of the&"frican ve2+ut of "frica& views to posit a segregation of central "fricans from the proto#modernpopulation in which speciation occurred. -ince they also claim that modern humans originated in andradiated from "frica, Tishoff (for instance! is driven to suggest that this hundreds of thousand year

se*uestration was somewhere in 3. . "frica.4

This is an implausible, ad hoc suggestion. 5y contrast, it is natural to suppose that separation implies

the population ancestral to humans was a part of the radiation out of "frica into urasia, before thespeciation event occurred. If the speciation event too place in urasia, we would e$pect that thedescendant population would show a &bottlenec& effect, and that those populations would possess lowgenetic diversity today, relative to central "fricans, which is what we do find.65y contrast, central "fricans

have always had a large effective population sie (Tishoff et al., 199!, and are characteried bye$traordinary diversity (7idd et al., 199!. "lso we would e$pect that "sians and uropeans would bemore closely related to each other than either are to "fricans, as is revealed in the discussion of cladisticsbelow. This view also accounts for the e$istence of the urasian types. 8et more impressive evidence for a

common urasian origin is the e$istence of a 4, year#old betaglobin linage common in "sia andrare in "frica (Harding et al., 1990! and the :ancient urasiatic marer;< 3=8 binary polymorphism 106,

whose particular significance is discussed below.

The age of the human species had lately been estimated at between 1>, and 4>, years,based on studies of mitochondrial ?3". Those estimates were based on the assumption of clonaltransmission of the mt?3", and the cited studies invalidate that ("wadalla et al., 1999@ Hagelberg et al.,1999@ yre#%aler et al., 1999!, but we do not now by how much the dates are off. yre#%aler has

proposed that &ve& may have lived twice as long ago as current estimates,)

or as long as >, years5A. If there were bottlenecs subse*uent to a mt?3" replacement event, which wiped out older lines, itwould seem that the sweep occurred more recently than it really did. "ccordingly, new estimates of s.sapiensage preclude the possibility that such a replacement event too place in, or mared the origin of,our species.

ore than one group of researchers (such as Harpending and /orde! consider that the data support a&clean sweep& of earlier mt?3" lineages and this has fre*uently been raised in support of the &ve2"frica&view. However, such ancient dates for an mt?3" replacement event would be consistent with radiation ofpre#human species out of "frica, rather than the origin of s. sapiens. There has never been any reason toassume that the putative female (whose mt?3" is said to be ancestral to that found in all living humans!was, herself, a s. sapiens. The entire basis for the &ve& hypothesis (that all modern, human mt?3"

originated with one woman, or even in one restricted population! is falsified by recent research indicatingplural lineages in the mt?3" genome. The putative B"frican veC is probably neither chronologically nor

causally related to the origin ofs. sapiens.

In this circumstance, it is only reasonable to assume that the date of the human cultural e$plosionsuggests the appro$imate era of s. sapiensspeciation. =esearch on the 8#chromosome yields an


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estimate of >9, years 5A for the :most recent common DpaternalE ancestor;, (Fnderhill, et al, 4!assuming no selection and population structure effects. Given that caveat, the #>9yr date fits those ofthe earliest human cultural remains lie a hand in a glove.

"bout forty thousand years ago, people from central "sia migrated into urope, and theirdescendants constitute a maority of the population there today (-emino Aassarina, 4! so we now

what typeof people they were. They came from the general area of those earliest human cultural sites,and they shared a genetic marer designated as 106. The population which carried that marer must

have e$isted for some time before their migration began, because derivative forms of it are found in

-iberia and the "merinds, which implies that it was present in their common ancestral population thate$isted prior to ), years 5A. "gain, we have a good idea of what that ancestral urasian type was,by inference from the populations it generated, and it seems liely to be as ancient as humanity itself.%hen was there time, within the human culture period, for evolution of the urasian ancestral type from"frican immigrantsJ oreover, the precursors to humanity are all present in urasia (fromH.ergaster, andheidelbergensis, through archaicsapiens! while no comparable se*uence has beendiscovered in "frica.

ven if, contrary to all the data adduced here, humanity had originated in "frica, it seems contrivedto assume that s. sapienswould have immediately migrated from that continent, to leave their earliest

nown (and all subse*uent! cultural artifacts in urasia. 5ut if (on the "fro#origins view! they did, whydidthey evolve into the urasian ancestral typeJ %hat mechanisms, events, and pressures would conduce to

such a changeJ %hy did those other populations, said to be Bfirst out of "fricaC (on account of their geneticdiversity! such as the "ndaman Islanders and tropical -. . "sian types, note$perience any such changeJ?o the "fro#origin people perhaps agreethat the speciation event created the urasian type fromarchaic sapiensJ The invocation of &genetic drift& and &founder effect&, as used to assert a counter#intuitive interpretation of the diversity gradient (Tishoff et al., 199!>,will not serve.

I believe it is incumbent upon those who support the view of s. sapiensorigins in "frica to e$plain

how and why they were converted to urasian types so *uicly. "nd those who maintain that humansoriginated long before they began to leave cultural artifacts need to e$plain why@ what changed, that

made them reallyhumanJ %hy would humans evolve, long ago in "frica, but only begin to behave liehumans once they arrived at northern latitudes< are we bac to the climate theory of evolutionJ TheauthorCs view is that the only logical interpretation of all the available data, including the characteristics of

e$tant populations, is that the speciation event occurred in a urasian population, of archaic sapiens, withancient indigenous roots, in which case it is obvious how s. sapiens' progenitors were se*uestered fromcentral "frica.

The current urasian populations are lightly pigmented, and that is associated with high latitudespecies and populations in many other genera. It has often been suggested that the ancient ancestors of

the urasian types were part of a population that had been resident at high latitudes long enough tomanifest the derived characteristic of light pigmentation. +n this view we would e$pect to find that light#

sinned people would display low diversity and a distant relationship to central "fricans, which is what wefind. In fact, the genetic difference between "fricans and uropeans is so distinct that the proportion ofuropean admi$ture in "fro#"mericans can be determined with a margin of error of only .4 (?estro#5isol et al., 1999!.

Harpending states that the population ancestral to s.sapienswas &small during most of theAleistocene& and that &the number of our ancestors ust before the e$pansion ('origin'! of modern humans

was small, only several thousand breeding adults.& %e can compare this characteriation of our ancestralpopulation with the evidence that "fricans have always had a large effective population sie. It is this

incongruity that forces Tischoff to postulate that the pre#human population was both &isolated from therest of the "frican continent& and &somewhere in 3. . "frica.&oreover, this would have been for a verylong time. Aerhaps in Kemuria or "tlantisJ

The evidence indicates that humans came from a sparse population in urasia@ that their diversitywas further reduced by the speciation event@ that they subse*uently e$panded in every habitabledirection@ and that they interbred with the populations they came in contact with, producing e$tant hybrid

populations. Hence ountain et al. (199)! reports that in the cladistic tree &the uropean branch issignificantly short relative to all other branches,& that &the neighbor#oining tree... places the uropean

sample close to the center of the tree with an e$tremely short branch,& and further that &uropeans andnortheast "sians are closely related.& The first two of these statements are inconsistent with origin and

radiation out of "frica while the third does not lend it any support.


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vidence for radiation into "frica was found by Hammer et al. (199! and Tischoff et al. (199!noted such evidence, but the latter went on to suggest that no attention should be paid to it.0Theradiation of low#diversity s. sapiensfrom urasia is also the best e$planation for the discoveries, dates,morphology and genetic data in -. . "sia. There, s. sapiensand erectuslived in pro$imity for as long as4, years (-wisher et al., 199!. -o many of the human fossils from this area and era show a mi$edsuite of s.sapiensand erectusfeatures that interbreeding is the most plausible interpretation of the data.any students of fossil morphology have long contended that there is continuity between -. . "sian

Hominid fossils and e$tant indigenous peoples.Genetic data show these populations are distinct fromnorthern "sian populations and of comparable diversity to "fricans (Lhang et al. 199!.9

The 3gandong specimens, in particular, have occasioned much debate on account of their mi$tureof s.sapiensand erectustraits and their affinities with "ustralians.1%e would e$pect that the crania ofsuch hybrids would show affinities to both species, and that is why these fossils are so hard to classify.-ome authorities say they are clearly erectus, while others point to modern traits, and especially that verysimilar sulls (from overlapping dates! are found in "ustralia. oreover, the traits in *uestion occur in themodern population. This is not merely consistent with, but constitutes strong evidence for, the view that

radiating, low#diversity s. sapiensinterbred with relic erectuspopulations, thus ac*uiring the near#"fricandiversity and primitive morphological traits manifest in the "sian fossil record and e$tant indigenes.

The hypothesis presented here uni*uely e$plains one particularly puling aspect of the "ustralianfossil record. The oldest fossils from "ustralia are the most modern in morphology. +n my view, this is

e$plained by the fact that the first wave of humans who passed through -. . "sia on their way to"ustralia were less hybridied with resident erectuspopulations because they spent less time living amongthem. Aopulations that settled "ustralia later (leaving the 7ow -wamp#type sulls! had been living in -. ."sia for as much as 4, years and were far more hybridied in conse*uence.

%olpoff accepts that the 3gandong sulls are representative of the population that produced the 7ow-wamp#type specimens, and left descendants in the modern population 5ut he e$plicitly reects the view,

as set forth here, that there was inter#species gene flow, and calls it &unacceptable&. This, however, is asocio#political rather than a scientific statement. He does not contend that it isnCt a reasonable

construction of the data, but reects it on grounds of dogma, because of its implication that some modernpopulations e$press a more primitive genome. %olpoff considers that the hypothesis of hybridiation is&unacceptable& because it &raises the specter that some human populations can be interpreted to differ

from others because they have more genes from an e$tinct, primitive human species.& Thus, according to%olpoff and other adherents of this doctrine, scientific truths which conflict with their politically#correct&ust so& paradigm are outside the bounds of contemplation. It is noteworthy that he is driven to contendthat erectusis human (BtrueCman! in order to preserve logical consistency M at the e$pense of commonsense.

The people of the "ndaman Islands have also been the subect of a study which has been reported as&supporting 'out of "frica.'&11This is an e$ample of the almost universal, and usually unstated, assumption

that there are only two possible hypotheses of human origins< the multi#regional, and "frican views. If thedata conflicts with the multi#regional view it is said to :support; "frican origin. This not only begs the*uestion, but is arguably deceitful. In this case, the data, considered by itself, may not contradict "fricanorigin, but as part of the pattern already noted above, it actually supports the opposing hypothesis

presented here. The "ndaman Islands are yet another of the places where s. sapiensinterbred with arelic erectus population, were hybridied, and e$isted in an isolated condition until the present. 3ot

surprisingly, they show genetic affinities to central "fricans, because (lie them, and some -. . "sians!they preserve substantial portions of the pre#human genome.

It is nonsense to suggest that the first groups of humans &out of "frica& immediately migrated to theends of the earth ("ndamans, "ustralia, 3ew Guinea, etc...! or that the populations of all such remoteplaces should possess such diversified and similar genomes by chance. The inferred pattern ofhybridiation is the more parsimonious hypothesis. They are found in these out#of#the#way placesbecause they were driven there by more advanced populations who supplanted such hybrids elsewhere.

8et another challenge e$ists to the claim that our species radiated out of "frica. There is a consensus

among anthropologists that s. sapiens' cultural artifacts indicate a higher level of cognitive function thanany previous species. The technical level and diversity of their tool industry alone would have set them

apart. "dd to that, whole new categories of behavior< the creation of representative art, the domesticationof the dog, etc... Thus, we would e$pect that populations which were hybridied with predecessor species

would be intellectually and cognitively disadvantaged in relation to low#diversity, urasian populations Infact, we do observe that (Herrnstein and urray, 199)!, which clearly reveals the direction of species


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radiation. $pressing this view, however, is liely to attract such vehement abuse that few dare. +nlythose whose livelihood is not subect to the fiats of &wimmin and minorities& can openly spea the truth onthis subect, and their views are ruthlessly censored.

3otes 1. Harpending, et al. (199!@ see especially the conclusions. 4. 6. Tishoff, -. "., from a report in

the -cience ?aily of 4> /anuary 1999 of a presentation at the annual meeting of the "merican "ssociationfor the "dvancement of -cience in "naheim on 44 /anuary. ). yre#%aler, '=ecent Ninds in

Aaleoanthropology' in "thena =eview vol. 4, no. 4 (1 arch 4!. >. -ee p. 169> and p. 1699, and

generally, to account for the observed diversity clines, which intuitively support radiation out of urasia bylow#diversity s. sapiens, gaining diversity as they interbred with pre#human populations subse*uent totheir speciation. . Tishoff, as *uoted in -cience ?aily (above!. 0. Tishoff et al. (199!. +n page 1699,she postulates a &dramatic& founder effect and genetic drift. . %olpoff, ilford H., submitted a postentitled &3o Homo erectus at 3gandong& to Human +rigins 3ews (http://www.pro-am.com/origins/news/article19.html ! on 1 arch 4. He is perhaps the best nown proponent of the viewthat there is continuity between the ancient and modern populations@ saying, for instance, that the

population represented by the 3gandong specimens is &incontrovertably& ancestral to some "ustralianfossils and living people. 9. Lhang et al. 199, p. 9 notes the way elanesians are genetically

differentiated from other Aacific islanders and "sians (citing Nlint et al. (1996!!. Their figures 6 > aresomewhat pertinent. ountain, op. cit., p. >1, notes clustering of pygmies and -. . "sians. Nigure 1

shows how representative global populations cluster< the pattern is consistent (in the author's

interpretation! with urasian hybridiation of a species whose genome subsumed the diversity of thecurrent (also hybridied! "fricans. 7idd, op. cit. p. 44>, cites Harding (1990! concerning variation ofbetaglobin in -. . "sians. /orde, op. cit., Nigure 4 shows -. . "sians clustering with pygmies. Hagelberg(as cited in 11, below! finds affinities between pygmies and "ndaman Islanders. 1. %olpoff's post (,above! seems to be in response to the statement of Ahilip =ightmire (cited as &an e$pert on the species&!in the 1> ?ecember 199 issue of Human +rigins 3ews that &They D3gandong specimensE areune*uivocally H. erectus.& 11. Hagelberg, . No$, L. K. in an unpublished study, *uoted in -cientific

"merican, '-cience and the Litien', /anuary 1999.

=eferences "wadalla A., yre#%aler "., -mith /. . (1999! 'Kinage ?ise*uilibrium and =ecombination inHominid itochondrial ?3"', -cience vol. 4, pp. 4>4)#4>4> (4) ?ecember!.Lhang N#., 7idd /. =.,Kiva 7. /., Aastis ". /., 7idd 7. 7. (199! 'The world#wide distribution of allele fre*uencies at the humandopamine ?) receptor locus', Human Genetics, 9< 91#11.?estro#5isol G., aviglia =., Laglia "., 5oschiI., -pedini G., Aascali O., Llar "., Tishoff -. (1999! 'stimating uropean admi$ture in "frican

"mericans by using microsatellites and a microsatellite haplotype (L?)2"lu!', Human Genetics 1)< 1)9#1>0. yre#%aler "., -mith 3. H., -mith /. . (1999! Aroceedings of the =oyal -ociety, Kondon -eries 5.

5iological -ciences 4, )00. Hagelberg . et al. (1999! Aroceedings of the =oyal -ociety, Kondon, -eries5. 5iological -ciences 4, )>. Hammer . N., 7arafet T., =asanayagam "., %ood . T., "ltheide T. 7.,

/enins T., Griffiths =. L., Templeton ". =., Pegura -. K. (199! '+ut of "frica and 5ac "gain< 3estedcladistic analysis of human 8 chromosome variation', olecular 5iological volution, "pril 1> ()!< )40#)1. Harding =. ., Nullerton -. ., Griffiths =. L., 5ond /., Lo$ . /., -chneider /. "., oulin ?. -., Llegg/. 5. (1990! '"rchaic "frican and "sian lineages in the genetic ancestry of modern humans', "merican/ournal of Human Genetics, "pril ()!< 004#9. Harpending H. L., 5ater . "., Gurven ., /orde K.5.,

=ogers ". =., and -herry -. T. (199! 'Genetic traces of ancient demography', Aroceedings of the 3ational"cademy of -cience, F-", vol. 9>, pp. 191#190.Herrnstein, =. /. and urray, L. The 5ell Lurve, (199)!-imon and -chuster (The Nree Aress! "lso< Kynn (1991!, Pindi (199)!, Kynn (199)!, -nyderman

=othman (190!, /ensen (1996!, /ensen %hang (1996!. /orde K. 5., =ogers ". =., 5amshad .,%atins %. -., 7raowia A., -ung -., 7ere, /. and Harpending H. L. (1990! 'icrosatellite diversity and

the demographic history of modern humans', Aroceedings of the 3ational "cademy of -ciences, F-", vol.9), pp. 61#616. 7idd 7. 7., 5harti ., Lastiglione L. ., Phao H., Aastis ". /., -peed %. L., 5onne#Tamir 5., Ku =#5., Goldman ?., Kee L., 3am 8.-., Grandy ?. 7., /enins T., 7idd /. =. (199! '" globalsurvey of haplotype fre*uencies and linage dise*uilibrium at the ?=?4 locus', Human Genetics 16< 411#440. ountain /. K. and Lavalli#-fora K. K. (199)! 'Inference of human evolution through cladisticanalysis of nuclear ?3" restriction polymorphisms', Aroceedings of the 3ational "cademy of -ciences,F-", vol. 91, pp. >1>#>19.-emino, +rnella Aassarino, Giuseppe (4! BThe Genetic Kegacy of

Aaleolithic Homo sapiens sapiens in $tant uropeans< " Y Chromosomeperspective.C Sciencevol. 49(>)9)! pp 11>># (3ov. 1!. -wisher III L. L., =in %. /., "nton -. L., -chwarc H. A., Lurtis G. H.,-uprio "., %idiasmoro (199! -cience, vol. 40) (>49)!, pp 10#10). Tishoff -. "., ?ietsch .,

-peed %., Aastis ". /. et al. (199! 'Global patterns of linage dise*uilibrium at the L?) locus andmodern human origins', -cience, %ashington, arch .Tishoff -. "., Goldman "., Lalafell N., -peed %.L., ?einard ". -., 5onne#Tamir 5., 7idd /. =., Aastis ". /., /enins T., and 7idd 7. 7. (199! '" Global
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Haplotype "nalysis of the yotonic ?ystrophy Kocus@ Implications for the volution of odern Humansand for the +rigin of yotonic ?ystrophy utations', "merican /ournal of Human Genetics, 4< 169#1)4. Fnderhill, Aeter "., Aeidong -hen, "lice Kin, Ki /in, Giuseppe Aassarino, %ei 8ang, rin 7auffman,5atsheva 5onne#Tamir, /aume 5ertranpetit, Aaolo Nrancalacci, utanser Ibrahim, Trefor /enins, /udith7idd, -. Qasim ehdi, ar -eielstad, =. %ells, "lberto Aiaa, =onald ?avis, arcus Neldman, K. Lavalli#sfora, Aeter +efner (4! Ketter, Nature Genetics; vol. 4, 3ovember.%olpoff, ilford H., in a postentitled< &3o Homo erectus at 3gandong& to Human +rigins 3ews (http

age and origin of the human species - human origins

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