than others In fact. all 14 human se- uences are nearl distant from the mba e sequences which implies FATHER MOTHER the rates of change among humans are The chimpanzee data also illustrated how remarkably homogeneous humans are at the genetic level: chimpanzees nly show as much as 10 times fact alone suggests that all of modern humanity sprang from a relatively small stock of common ancestors working at Berkeley with Stone w'e expanded on Kocher's work amining a larger genealogical tree made up from 182 distinct types of mitochon-MALE drial DNA from 241 individuals. The FEMale multiple occurrences of mitochondrial people from the same continent and MITOCHONDRIAL DNA SOURCE usuallyin persons who lived within pEDigree of one individual illustrates the difference between the patterns of nu- 100 miles of one another. Because the clear and mitochondrial inheritance. All 32 ancestors from five generations ago tree we constructed had two main contributed equally to his nuclear DNA. His mitochondrial lineage(blue line)leads branches, both of which led back to back to only one person in every generation sis that Africa was the place of origin for modern humans ike biological species. We propose that light skin color of many whites One point that jumps out of our the anatomic characteristics uniting ably a late development that study is that although geographic bar- New Guineans were not inherited from in Europe after that continent riers do influence a population's mito- the first settlers. They evolved after nized by Africans chondrial DNA, people from a given people colonized the island, chiefly as During the 980s, when we were continent do not generally all belong to the result of mutations in nuclear constructing analogical tree. we the same maternal lineage. The New genes spread by sex and recombination had to rely or Americans as sub Guineans are typical in this respect. throughout New Guinea. Similarly, the stitutes for Africans, whose mitochon- remarkable variety of language fami lies-generally classified as papuan oken on this one island [see"The 2 Austronesian Dispersal and the Origin by Pet FIc AMERICAN, July 19911. On our genealogical tree, New Guineans showed up on several different branches, which 5 proved that the common female ances tor of all New guineans was not some. one in New Guinea. The population of New guinea must have been founded by many mothers whose maternal lin- eages were most closely related to 29 those in asia That finding is what one would ex- pect if the African origin hypothesis were true: as people walked east out of 12 Africa, they would have passed through Asia. Travel was probably slow, and 13 during the time it took to reach New 14 Guinea, mutations accumulated both in the lineages that stayed in Asia and in those that moved on e who are apparently re- lated by membership in a common ge- UNIVERSAL MATERNAL ANCESTOR can be found for all the members of any pop- graphic race need not be very closely ulation. The example traces the lineages of 15 females in a stable population. In related in their mitochondrial dNa ach generation, some maternal lineages proliferate and others become extinct. tochondrially speaking, races are not Eventually, by chance, one maternal lineage replaces all the others SCIENTTFIC AMERICAN April 1992than others. In fact. all 14 human se￾quences are nearly equidistant from the chimpanzee sequences, which implies the rates of change among humans are fairly uniform. The chimpanzee data also illustrated how remarkabl). homogeneous humans are at the genetic level: chimpanzees ’ commonly show as much as 10 times the genetic variation as humans. That fact alone suggests that all of modern humanit). sprang from a relativeI), small stock of common ancestors. 1Vorking at Berkeley, rlith Stoneking. \vc espanded on Kochcr’s bvork bl, cx￾amining a larger genealogical tree made up from 182 distinct t)-pes of mitochon￾drial DNA from 241 indhiduals. The multiple occurrences of mitochondrial DNA t)‘pcs %verc ahva).s found among people from the same continent and usuall~~ in persons \\,ho lived rsithin 100 miles of one another. Because the tree we constructed had two main branches, both of which led back to Africa, it, too, supported the hypothe￾sis that Africa was the place of origin for modern humans. One point that jumps out of our study is that although geographic bar￾riers do influence a population’s mito￾chondrial DNA, people from a given continent do not generally all belong to the same maternal lineage. The New Guineans are typical in this respect. Their genetic diversity had been sus￾pected from linguistic analyses of the remarkable variety of language fami￾lies-generally classified as Papuan￾spoken on this one islsnd [see “The Austronesian Dispersal and the Origin of Languages,” by Peter Bellwood; SCI￾ENTIFIC AMERICAN, July 19911. On our genealogical tree, New Guineans showed up on several different branches, which proved that the common female ances￾tor of all New Guineans was not some￾one in New Guinea. The population of New Guinea must have been founded by many mothers whose maternal lin￾eages Lvere most closely related to those in Asia. That finding is what one would ex￾pect if the African origin hypothesis were true: as people walked east out of Africa, they would have passed through Asia. Travel was probably slow, and during the time it took to reach New Guinea, mutations accumulated both in the lineages that stayed in Asia and in those that moved on. Thus, people who are apparently re￾lated by membership in a common ge￾ographic race need not be very closely related in their mitochondrial DNA. Mi￾tochondrially speaking, races are not MALE l FEMALE 4 SON - MITOCHONDdL DNA SOURCE PEDIGREE of one individual illustrates the difference between the patterns of nu￾clear andmitochondrial inheritance. All 32 ancestors from five generations ago contributed equally to his nuclear DNA. His mitochondrial lineage (blue line) leads back to only one person in every generation. like biological species. We propose that the anatomic characteristics uniting New Guineans were not inherited from the first settlers. They evolved after people colonized the island, chiefly as the result of mutations in nuclear genes spread b). sex and recombination throughout New Guinea. Similarly, the light skin color of many whites is prob￾ably a late development that occurred in Europe after that continent was colo￾nized b). Africans. During the early 198Os, when we were constructing our genealogical tree, we’ had to rely on black Americans as sub: stitutes for Africans, whose mitochon￾UNIVERSAL MATERNAL ANCESTOR can be found for all the members of any pop￾ulation. The example traces the lineages of 15 females in a stable population. In each generation, some maternal lineages proliferate and others become extinct. Eventually, by chance, one maternal lineage replaces all the others. SCIENTIFIC AMERICA Apt-d 1992 71