A quest to understand how human intelligence evolved raises some ethical questions.
Human intelligence is one of
evolution’s most consequential inventions. It is the result of a sprint
that started millions of years ago, leading to ever bigger brains and
new abilities. Eventually, humans stood upright, took up the plow, and
created civilization, while our primate cousins stayed in the trees.
Now scientists in southern China report that they’ve tried to narrow the evolutionary gap, creating several transgenic macaque monkeys with extra copies of a human gene suspected of playing a role in shaping human intelligence.
“This was the first attempt to understand the evolution of human cognition using a transgenic monkey model,” says Bing Su, the geneticist at the Kunming Institute of Zoology who led the effort.
According to their findings, the modified monkeys did better on a memory test involving colors and block pictures, and their brains also took longer to develop—as those of human children do. There wasn’t a difference in brain size.
The experiments, described on March 27 in a Beijing journal, National Science Review, and first reported by Chinese media, remain far from pinpointing the secrets of the human mind or leading to an uprising of brainy primates.
Now scientists in southern China report that they’ve tried to narrow the evolutionary gap, creating several transgenic macaque monkeys with extra copies of a human gene suspected of playing a role in shaping human intelligence.
“This was the first attempt to understand the evolution of human cognition using a transgenic monkey model,” says Bing Su, the geneticist at the Kunming Institute of Zoology who led the effort.
According to their findings, the modified monkeys did better on a memory test involving colors and block pictures, and their brains also took longer to develop—as those of human children do. There wasn’t a difference in brain size.
The experiments, described on March 27 in a Beijing journal, National Science Review, and first reported by Chinese media, remain far from pinpointing the secrets of the human mind or leading to an uprising of brainy primates.
Instead, several Western scientists, including one who collaborated
on the effort, called the experiments reckless and said they questioned
the ethics of genetically modifying primates, an area where China has
seized a technological edge.
“The use of transgenic monkeys to study human genes linked to brain
evolution is a very risky road to take,” says James Sikela, a
geneticist who carries out comparative studies among primates at the
University of Colorado. He is concerned that the experiment shows
disregard for the animals and will soon lead to more extreme
modifications. “It is a classic slippery slope issue and one that we can
expect to recur as this type of research is pursued,” he says.
Research using primates is increasingly difficult in Europe and the
US, but China has rushed to apply the latest high-tech DNA tools to the
animals. The country was first to create monkeys altered with the gene-editing tool CRISPR, and this January a Chinese institute announced it had produced a half-dozen clones of a monkey with a severe mental disturbance.
“It is troubling that the field is steamrolling along in this manner,” says Sikela.
Evolution story
Su, a researcher at the Kunming Institute of Zoology, specializes
in searching for signs of “Darwinian selection”—that is, genes that have
been spreading because they’re successful. His quest has spanned such
topics as Himalayan yaks’ adaptation to high altitude and the evolution
of human skin color in response to cold winters.
The biggest riddle of all, though, is intelligence. What we know is
that our humanlike ancestors’ brains rapidly grew in size and power. To
find the genes that caused the change, scientists have sought out
differences between humans and chimpanzees, whose genes are about 98%
similar to ours. The objective, says, Sikela, was to locate “the jewels of our genome”—that is, the DNA that makes us uniquely human.
For instance, one popular candidate gene called FOXP2—the
“language gene” in press reports—became famous for its potential link to
human speech. (A British family whose members inherited an abnormal
version had trouble speaking.) Scientists from Tokyo to Berlin were soon
mutating the gene in mice and listening with ultrasonic microphones to
see if their squeaks changed.
Su was fascinated by a different gene: MCPH1, or
microcephalin. Not only did the gene’s sequence differ between humans
and apes, but babies with damage to microcephalin are born with tiny
heads, providing a link to brain size. With his students, Su once used
calipers and head spanners to the measure the heads of 867 Chinese men
and women to see if the results could be explained by differences in the
gene.
By 2010, though, Su saw a chance to carry out a potentially more
definitive experiment—adding the human microcephalin gene to a monkey.
China by then had begun pairing its sizable breeding facilities for
monkeys (the country exports more than 30,000 a year) with the newest
genetic tools, an effort that has turned it into a mecca for foreign scientists who need monkeys to experiment on.
To create the animals, Su and collaborators at the Yunnan Key
Laboratory of Primate Biomedical Research exposed monkey embryos to a
virus carrying the human version of microcephalin. They generated 11
monkeys, five of which survived to take part in a battery of brain
measurements. Those monkeys each have between two and nine copies of the
human gene in their bodies.
Su’s monkeys raise some unusual questions about animal rights. In 2010, Sikela and three colleagues wrote a paper called “The ethics of using transgenic non-human primates to study what makes us human,”
in which they concluded that human brain genes should never be added to
apes, such as chimpanzees, because they are too similar to us. “You
just go to the Planet of the Apes immediately in the popular
imagination,” says Jacqueline Glover, a University of Colorado
bioethicist who was one of the authors. “To humanize them is to cause
harm. Where would they live and what would they do? Do not create a
being that can’t have a meaningful life in any context.”
The authors concluded, however, that it might be acceptable to make such changes to monkeys.
In an e-mail, Su says he agrees that apes are so close to humans
that their brains shouldn’t be changed. But monkeys and humans last
shared an ancestor 25 million years ago. To Su, that alleviates the
ethical concerns. “Although their genome is close to ours, there are
also tens of millions of differences,” he says. He doesn’t think the
monkeys will become anything more than monkeys. “Impossible by
introducing only a few human genes,” he says.
Smart monkey?
Judging by their experiments, the Chinese team did expect that
their transgenic monkeys could end up with increased intelligence and
brain size. That is why they put the creatures inside MRI machines to
measure their white matter and gave them computerized memory tests.
According to their report, the transgenic monkeys didn’t have larger
brains, but they did better on a short-term memory quiz, a finding the
team considers remarkable.
Several scientists think the Chinese experiment didn’t yield much
new information. One of them is Martin Styner, a University of North
Carolina computer scientist and specialist in MRI who is listed among
the coauthors of the Chinese report. Styner says his role was limited to
training Chinese students to extract brain volume data from MRI images,
and that he considered removing his name from the paper, which he says
was not able to find a publisher in the West.
“There are a bunch of aspects of this study that you could not do
in the US,” says Styner. “It raised issues about the type of research
and whether the animals were properly cared for.”
After what he’s seen, Styner says he’s not looking forward to more
evolution research on transgenic monkeys. “I don’t think that is a good
direction,” he says. “Now we have created this animal which is different
than it is supposed to be. When we do experiments, we have to have a
good understanding of what we are trying to learn, to help society, and
that is not the case here.” One issue is that genetically modified
monkeys are expensive to create and care for. With just five modified
monkeys, it’s hard to reach firm conclusions about whether they really
differ from normal monkeys in terms of brain size or memory skills.
“They are trying to understand brain development. And I don’t think they
are getting there,” says Styner.
In an e-mail, Su agreed that the small number of animals was a
limitation. He says he has a solution, though. He is making more of the
monkeys and is also testing new brain evolution genes. One that he has
his eye on is SRGAP2C, a DNA variant that arose about two million years ago, just when Australopithecus was ceding the African savannah to early humans. That gene has been dubbed the “humanity switch” and the “missing genetic link” for its likely role in the emergence of human intelligence.
Su says he’s been adding it to monkeys, but that it’s too soon to say what the results are.
