快猫短视频

WE LOOK pretty different from our closest relatives, the chimps, but we鈥檇
probably be classified in the same genus if we only had DNA to go on. So say
Ajit Varki and Pascal Gagneux from the University of California in San Diego,
who鈥檝e been studying the known genetic differences between humans and our
primate cousins. The researchers claim that because we鈥檙e so similar, only full
sequencing of chimp DNA will tell us which genes make us human.

鈥淚f you were looking down from outer space and simply took the DNA
differences we would certainly fall into one group with the chimpanzees and
bonobos. It is the gorillas and the orang-utans who are the outliers,鈥� Varki
says.

Chimps and humans share around 99 per cent of their DNA and so far only one
major difference has been found. Humans lack a certain sugar which is found on
the surface of the body cells of other mammals, including great apes. 鈥淲e have
some intriguing clues to the effects this might have,鈥� says Varki, which he
suspects could include changes in brain development and susceptibility to
viruses or bacteria.

Sequencing the chimp genome is now a 鈥渕oral imperative鈥�, according to Varki.
Comparing the sequences should help us find out which genes make us human. There
would also be medical benefits. Chimps are particularly resistant to a number of
human diseases, including AIDS, Alzheimer鈥檚, malaria and many common cancers, so
any genetic differences could lead to new ways of tackling these diseases.

Svante P盲盲bo of the Max Planck Institute for Evolutionary
Anthropology in Leipzig says that if we did compare the two genomes, we would
probably be humbled by how similar our two species are. 鈥淧erhaps it is this
expectation that explains the slowness with which the genomics community has
embraced the idea of a chimpanzee genome project,鈥� he says.

But P盲盲bo has found one thing that sets us apart from the other
primates. Different people have DNA that is almost identical, differing only 0.1
per cent of the time, or 1 in every 1000 DNA base pairs, while chimps have four
times as many differences. In an analysis of 10,000 base pairs of non-coding DNA
sequences from humans, chimps, gorillas and orang-utans, P盲盲bo and his
team found that within all the other species there is much more variation than
in people. 鈥淗umans are unique compared with the great apes in having little
genetic variation,鈥� says P盲盲bo.

The researchers say this supports the notion that humans evolved from a small
group of ancestors, while other great apes are descended from much larger
populations. 鈥淗ad the Neanderthals or other archaic humans survived until today,
contemporary humans would perhaps have been more like the great apes in terms of
genetic diversity,鈥� says P盲盲bo.

According to the results, humans are also a much younger species. We are
descended from a common ancestor which existed around half a million years ago,
while the common ancestors of chimps, orang-utans and gorillas existed around 1
to 2 million years ago.