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Findings could simplify human lineage

Oct. 17, 2013
Courtesy of Science
and World Science staff

Sev­er­al an­ces­tral forms of hu­mans were really one spe­cies, not sep­a­rate ones as pre­vi­ously thought, ac­cord­ing to new re­search.

The find­ings are based on an anal­y­sis of a com­plete skull of a hom­i­nid, or hu­man-like crea­ture, from Dman­isi, Geor­gia, dat­ed to about 1.8 mil­lion years ago.

Dmanisi "skull 5." (Credit: Gu­ram Bum­biash­vi­li, Geor­gian Nat'l Mu­seum)


The work sug­gests that the ear­li­est mem­bers of the ge­nus, or cat­e­go­ry of re­lat­ed crea­tures, known as Ho­mo (“man”) were ac­tu­ally the same spe­cies. A ge­nus is a cat­e­go­ry con­sist­ing of one or more spe­cies. Our own spe­cies is Ho­mo sa­piens.

These ear­li­est mem­bers of the Ho­mo ge­nus in­clud­ed the spe­cies Ho­mo ha­bilis, Ho­mo ru­dolf­en­sis, and Ho­mo erec­tus, ac­cord­ing to the prevail­ing way of think­ing. 

These early hu­man an­ces­tors probably just looked dif­fer­ent, ac­cord­ing to re­search­ers. Da­vid Lord­kipanidze of the Geor­gian Na­t­ional Mu­se­um and col­leagues stud­ied the skull, which was dis­cov­ered along­side the re­mains of four oth­er early hu­man an­ces­tors, all of them as­so­ci­at­ed with the same ar­ea and time. 

But, un­like oth­er Ho­mo fos­sils on rec­ord, this skull, known as Skull 5, com­bines a small brain­case with a long face and large teeth—fea­tures not be­fore seen to­geth­er in an early Ho­mo fos­sil, ac­cord­ing to the sci­en­tists.

Giv­en their di­verse phys­i­cal traits, the Dman­isi finds can be com­pared to var­i­ous Ho­mo fos­sils, in­clud­ing those found in Af­ri­ca, dat­ing back to about 2.4 mil­lion years ago, and oth­ers dis­cov­ered in Asia and Eu­rope, which are dat­ed be­tween 1.8 and 1.2 mil­lion years ago, the in­ves­ti­ga­tors added.

Re­search­ers have tra­di­tion­ally used such varia­t­ion among Ho­mo fos­sils to de­fine sep­a­rate spe­cies, but Lord­kipanidze and his team say that the varia­t­ion be­tween the fos­sils at Dman­isi is no more pro­nounced than that seen be­tween five mod­ern hu­mans or five chim­panzees. 

In light of these find­ings, the re­search­ers pro­pose that ear­ly, di­verse Ho­mo fos­sils, with their ori­gins in Af­ri­ca, ac­tu­ally rep­re­sent varia­t­ion among mem­bers of a sin­gle, evolv­ing lin­eage—most ap­pro­pri­ate­ly, in their view, Ho­mo erec­tus

The re­search ap­pears in the Oct. 18 is­sue of the jour­nal Sci­ence.


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Several ancestral forms of humans were really one species, not separate ones as previously thought, according to new research. The findings are based on an analysis of a complete skull of a hominid, or human-like creature, from Dmanisi, Georgia, dated to about 1.8 million years ago. The work suggests that the earliest members of the genus, or category of related creatures, known as Homo (“man”) were actually the same species. A genus is a category consisting of one or more species. These earliest members of the Homo genus included species such as Homo habilis, Homo rudolfensis, and Homo erectus. These early human ancestors probably just looked different, according to researchers. David Lordkipanidze of the Georgian National Museum and colleagues studied the skull, which was discovered alongside the remains of four other early human ancestors, all of them associated with the same area and time. But, unlike other Homo fossils on record, this skull, known as Skull 5, combines a small braincase with a long face and large teeth—features that had not been observed together in an early Homo fossil until now, according to the scientists. Given their diverse physical traits, the Dmanisi finds can be compared to various Homo fossils, including those found in Africa, dating back to about 2.4 million years ago, and others discovered in Asia and Europe, which are dated between 1.8 and 1.2 million years ago, the investigators added. Researchers have traditionally used such variation among Homo fossils to define separate species, but Lordkipanidze and his team say that the variation between the fossils at Dmanisi is no more pronounced than that observed between five modern humans or five chimpanzees. In light of these findings, the researchers propose that early, diverse Homo fossils, with their origins in Africa, actually represent variation among members of a single, evolving lineage—most appropriately, in their view Homo erectus. This research appears in the 18 October 2013 issue of the journal Science.