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After jeers, some recognition for “reverse evolution” theorist

March 3, 2008
World Science staff

Af­ter two years in which he some­times tast­ed rid­i­cule, there is now some rec­og­ni­tion for a Turk­ish sci­ent­ist who claims ev­o­lu­tion may have gone back­ward in some un­usu­al coun­try­men of his. Phys­i­olo­g­ist Un­er Tan’s lat­est re­search on the peo­ple—who have walked on all fours life­long—is set to ap­pear in one of the most pres­tig­ious sci­en­tif­ic jour­nals. 

In the re­search, Tan and col­leagues iden­ti­fy a gene linked to the con­di­tion, which they call Un­er­tan syn­drome.

Some people affected by "Unertan syndrome." (Courtesy BBC)


Tan de­scribed him­self as “ex­tremely hap­py” about the pub­lica­t­ion. The find­ings are to ap­pear this week in the on­line early edi­tion of the U.S. jour­nal Pro­ceed­ings of the Na­tional Acad­e­my of Sci­ences. The jour­nal is of­ten cit­ed as one of the three most in­flu­en­tial sci­en­tif­ic jour­nals over­all by Thom­son Sci­en­tif­ic, a com­pa­ny that pub­lishes widely used jour­nal rank­ings.

The pub­lica­t­ion comes af­ter Tan, fac­ing skep­ti­cism and some­times hos­til­ity, had long dif­fi­cul­ties in get­ting his stud­ies on the syn­drome pub­lished in ma­jor jour­nals.

Con­tro­ver­sy fol­lowed Tan ev­er since he pro­posed his re­verse-ev­o­lu­tion the­o­ry, which along with the syn­drome it­self was first re­ported to the gen­er­al pub­lic in World Sci­ence. The the­o­ry—not dis­cussed in the Pro­ceed­ings pa­per—holds that the syn­dome may be a ge­net­ic throw­back to our ape-like an­ces­tors’ walk­ing style, and thus could shed light on it. 

Some sci­ent­ists have called the idea highly im­plau­si­ble. They ar­gue that any muta­t­ion caus­ing mod­ern peo­ple to walk on all fours must in­volve a sin­gle ge­net­ic change, where­as the ev­o­lu­tion­ary tran­si­tion to up­right walk­ing probably in­volved many changes.

Oth­ers who dis­a­gree with Tan have gone fur­ther and ac­cused him of slop­py schol­ar­ship and even er­rat­ic be­hav­ior. The sci­en­tif­ic de­bate has been com­pli­cat­ed by bit­ter, more per­son­al dis­putes be­tween Tan and some col­leagues, as well by what some ob­servers have called a circus-like at­mos­phere that sur­rounded the syn­drome’s dis­cov­ery in 2006.

Yet amid these con­tro­ver­sies, some re­search­ers called Tan’s re­verse-ev­o­lu­tion hy­poth­e­sis plau­si­ble and test­a­ble. Rev­erse ev­o­lu­tion—an or­gan­is­m’s re­turn to ge­net­ic char­ac­ter­is­tics of its an­ces­tors—has been doc­u­mented to oc­cur in some an­i­mals, such as fish that lose their eyes af­ter liv­ing in dark caves for genera­t­ions.

The new pa­per, co-authored with six of Tan’s col­leagues in­clud­ing his wife, Meliha, re­ports that a re­spon­si­ble muta­t­ion has been found in two of four fam­i­lies that by now have turned up af­fect­ed by “Uner­tan syn­drome.”

“Hu­man mo­lec­u­lar ge­net­ics in Tur­key is ‘on the map’ with this el­e­gant anal­y­sis,” said Mary-Claire King, a ge­net­icist at the Uni­ver­s­ity of Wash­ing­ton and an ed­i­tor of the Pro­ceed­ings.

The muta­t­ion is thought to af­fect brain de­vel­op­ment, though how pre­cisely it may lead to the un­usu­al walk­ing style is un­clear. Or­gan­isms that move on all fours are called quadrupeds.

Since the in­tial re­port of the syn­drome, Tan and col­leagues have iden­ti­fied three more Turk­ish fam­i­lies af­fect­ed. The Pro­ceed­ings pa­per re­ports that mem­bers of two of the fam­i­lies suf­fer a muta­t­ion in a gene called VLDLR, which in­flu­ences how new brain cells find their way to the right place in the de­vel­op­ing brain. One brain re­gion af­fect­ed is the cer­e­bel­lum, which gov­erns bal­ance for walk­ing and stand­ing. 

In a third fam­i­ly—that of the first dis­cov­ered cases of the syn­drome—Tan’s group con­firmed a pre­vi­ous study link­ing their muta­t­ion to a re­gion of a chro­mo­some called 17p. The re­gion is be­lieved to be one of the ar­eas of great­est dif­fer­ences be­tween hu­mans and chimps. Tan has said that this find­ing sup­ports his re­verse-ev­o­lu­tion idea. Al­though the new pa­per did­n’t go in­to that, he said he ex­pects fu­ture stud­ies to look at this issue. Probably “many genes are in­volved,” he added.


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After two years in which he sometimes tasted ridicule, there is now some recognition for a Turkish scientist who claims evolution may have gone backward in some unusual countrymen of his. Physiologist Uner Tan’s latest research on the people—who have walked on all fours lifelong—is set to appear in one of the most prestigious scientific journals. In the research, Tan and colleagues identify genes linked to the condition that Tan said may be a form of reverse evolution. The condition, dubbed Unertan syndrome by Tan and his team, leads people to walk on all fours habitually even as adults. Tan described himself as “extremely happy” about the publication. The findings are to appear this week in the online early edition of the U.S. journal Proceedings of the National Academy of Sciences. The journal is often cited as one of the three most influential scientific journals overall by Thomson Scientific, a company that publishes widely used journal rankings. The publication comes after Tan, facing skepticism and sometimes hostility, had long difficulties in getting his studies on the quadrupeds published in major scientific journals. Controversy surrounded Tan ever since he proposed his reverse-evolution theory, which along with the syndrome itself was first reported to the general public in World Science. The theory—not discussed in the new paper—holds that the syndome may be a genetic throwback to our ape-like ancestors’ walking style, and thus could shed light on it. Some scientists have called the idea highly implausible. They argue that any mutation causing modern people to walk on all fours must involve a single genetic change, whereas the evolutionary transition to upright walking probably involved many changes. Others who disagree with Tan have gone further and accused him of sloppy scholarship and even erratic behavior. The scientific debate has been complicated by bitterly personal disputes between Tan and certain colleagues, as well by what some observers have called a circus-like atmosphere that surrounded the syndrome’s discovery in 2006. Yet amid these controversies, some researchers called Tan’s reverse-evolution hypothesis plausible and testable. Reverse evolution—an organism’s return to genetic characteristics of its ancestors—has been documented to occur in some animals, such as fish that lose their eyes after living in dark caves for generations. The new paper, co-authored with six of Tan’s colleagues including his wife, Meliha, reports that a responsible mutation has been found in two of four families that by now have turned up affected by “Unertan syndrome.” “Human molecular genetics in Turkey is ‘on the map’ with this elegant analysis,” said Mary-Claire King, a geneticist at the University of Washington and the editor of the Proceedings. The mutation is thought to affect brain development, though how precisely it may lead to the unusual walking style is unclear. Organisms that move on all fours are called quadrupeds. Since the intial report of the syndrome, Tan and colleagues have identified three more Turkish families affected. The Proceedings paper reports that members of two of the families suffer a mutation in a gene called VLDLR, which influences how new brain cells find their way to the right place in the developing brain. One brain region affected is the cerebellum, which governs balance for walking and standing. In a third family—those of the original case—Tan’s group confirmed a previous study linking their mutation to a region of a chromosome called 17p, believed to be one of the areas of greatest differences between humans and chimps. Tan has said that this finding supports his reverse-evolution idea. Although the new paper didn’t go into that, he said he expects future studies to look at this. Probably “many genes are involved,” he added.