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Mutation may contribute to human uniqueness

May 8, 2007
Courtesy John Wiley & Sons, Inc.
and World Science staff

Sci­en­tists have iden­ti­fied a mu­ta­tion that they say could help ex­plain why hu­man cog­ni­tive abil­i­ties are so dif­fer­ent from those of other an­i­mals.

Past searches for such gene­tic chan­ges have had spot­ty suc­cess. A study last year did find mu­ta­tions unique to hu­mans in a gene called HAR1F, tied to brain de­vel­op­ment and pos­si­bly brain size. But it did­n’t clar­i­fy for cer­tain wheth­er the gene al­so en­hances men­tal ca­pac­i­ties. An­other gene, called FOXP2, has been linked to lang­uage abil­i­ties.
The new study found that hu­man brains have a unique form of a mol­e­cule im­pli­cat­ed in learn­ing and mem­o­ry, called neu­ro­p­sin. 

This new form would have orig­i­nat­ed less than five mil­lion years ago—lat­er than when the hu­man line­age split off in ev­o­lu­tion from its clos­est an­ces­tors, chimps, some six mil­lion years ago. Hu­mans and chimp genomes vary by an es­ti­mated 1.2 per­cent. 

The study is to ap­pear in an up­com­ing on­line is­sue of the re­search jour­nal Hu­man Mu­ta­tion.

Bing Su of the Chin­ese Acad­e­my of Sci­ences in Kun­ming, Chi­na and col­leagues an­a­lyzed hu­mans and sev­er­al spe­cies of apes and mon­keys. They found that hu­mans alone had a particularly long form of the neu­ropsin mol­e­cule called type II neu­ropsin. Al­though the pre­cise func­tion of neu­ropsin, a pro­tein, re­mains un­clear, it has been found in mice to help con­trol a pro­cess that un­der­lies learn­ing and mem­o­ry for­ma­tion. In this pro­cess, called long-term po­ten­ti­a­tion, new infor­ma­tion prompts brain cells to grad­u­al­ly change their ten­den­cies to pass along sig­nals to oth­er cells.

The change in the protein, Su and colleagues said, was in turn due to a change in a so-called splic­ing site of the gene that codes for its pro­d­uct­ion. This in es­sence means the gene’s code is edited dif­fer­ently as it’s used to create a fin­ished mol­e­cule. The find­ings “un­der­score the po­ten­tial im­por­tance of the cre­a­tion of nov­el splic­ing forms in the cen­tral nerv­ous sys­tem in the emer­gence of hu­man cog­ni­tion,” the re­search­ers wrote. They added that fu­ture re­search will have to clar­i­fy fur­ther what type II neu­ro­p­sin does.

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Scientists have identified a mutation that, they claim, could specifically help explain why human cognitive abilities are so different from those of other animals. Previous research has had spotty success in identifying such genes. A study last year did find a mutation unique to humans and tied to brain development and possibly brain size, in a gene called HAR1F. But the work didn’t clarify for certain whether the gene also enhances mental capacities. The new study found that human brains have a unique form of a molecule implicated in learning and memory, called neuropsin. The new form originated less than five million years ago, later than when the human lineage split off in evolution from its closest ancestors, chimps, researchers said. Humans and chimp genomes vary by just 1.2 percent. The study is to appear in an upcoming online issue of the research journal Human Mutation. Bing Su of the Chinese Academy of Sciences in Kunming, China and colleagues analyzed the DNA of humans and several species of apes and monkeys. They found that humans alone had a particularly long form of the neuropsin molecule called type II neuropsin. Although the precise function of neuropsin, a protein, remains unclear, it has been found in mice to help control a process that underlies learning and memory formation. In this process, called long-term potentiation, new information prompts brain cells to gradually change their tendencies to pass along signals to other cells. The change in neuropsin was in turn due to a change in the so-called “splicing site” of the neuropsin gene, the researchers said. This in essence means that the gene’s code is edited somewhat differently during the process of converting the code into a finished molecule. The findings “underscore the potential importance of the creation of novel splicing forms in the central nervous system in the emergence of human cognition,” the researchers wrote. They added that future research will have to clarify exactly what type II neuropsin does.