14 | New Scientist | 28 March 2020
News
Human geneticsA MINUSCULE meteorite unlike
any other we have discovered could
help us understand the kinds of
rocks that fill our solar system.
Maitrayee Bose at Arizona State
University and her colleagues
analysed the chemicals in a
2-millimetre meteorite found in
Antarctica, called TAM19B-7. When
they looked at the different carbonisotopes in the micrometeorite,
they were in for a surprise.
“Some of the areas in the
micrometeorite have the exact
same composition as Earth,” says
Bose. “But there were some regions
that were carbon-13-rich hotspots,
which is something that we didn’t
expect to find at all.”
The team spotted four of these
little pockets of heavy carbon.
The research was to have been
presented at the now-cancelled
Lunar and Planetary Science
Conference in Texas.The oxygen levels in the
micrometeorite didn’t match
any known asteroid. It is usually
possible to match a micrometeorite
to the asteroid family it belongs to,
although not with this sample.
But we know its parent rock
contained frozen water because
of the abundance of other isotopes
in the micrometeorite, primarilythose of oxygen, says Bose.
“It comes from a body that has
lots of ice, and when that ice melts
it interacts with the rock,” she says.
“The question is: can you make
important, life-critical compounds
by this interaction with water?”
On Earth, reactions between
water and rocks can form sugars,
amino acids and other chemicals
important for life. Finding the
micrometeorite’s mysterious parent
could help us figure out if similar
activity can occur on asteroids. ❚ANCIENT human populations
in Africa probably mixed far more
than we previously thought. That
is just one of the revelations about
our genetic history uncovered
by sequencing the genomes of
people from populations that
have been under-represented
in human genetic studies.
“We identified a lot of genetic
variation that had not been found
before,” says Anders Bergström
at the Wellcome Sanger Institute
in Hinxton, UK.
Bergström and his colleagues
sequenced the genomes of
929 people from 54 populations
across the globe, including from
Europe, the Middle East, Africa,
the Americas, Central and South
Asia, East Asia and Oceania. They
discovered hundreds of thousands
of new gene variants that had
previously been missed in existing
data sets (Science, doi.org/dp6n).
One discovery that Bergström
and his colleagues made was
that there was probably much
more mixing between different
ancient human populations in
Africa than suggested by previous
studies. Rather than a diverging
family tree, they found evidence
for gene flow between differentpopulations. “It’s more like a kind
of intertangled mesh of branches,”
says Bergström.
This hints at how ancient
humans migrated out of Africa.
Rather than a population
separating into two and each
part never seeing the other again,
people probably continued
to move between groups in
a more complex way, he says.
The team also found more
detailed evidence of our ancient
human ancestors mating with
other hominins. We already knewthat our ancestors mated with
archaic human groups, including
Neanderthals and Denisovans,
but until now it wasn’t clear
how frequently this occurred
or whether they mated with
some groups more than others.
Bergström and his team were
able to show that people from
many different populations
around the world today have thesame segments of Neanderthal
DNA in their genomes, but
segments of Denisovan DNA
differ between people in different
populations. That suggests that
our species probably mated with
a single Neanderthal group but
with multiple Denisovans after
migrating out of Africa.
Analysis of the new data,
which included whole genome
sequences from people with
Native American ancestry, also
hints that there may have been
many more early humans in
the Americas about 15,000 years
ago than previously thought.
“Our current genetic studies
and infrastructure are vastly
Eurocentric,” says Alicia Martin
at the Broad Institute in
Massachusetts. “To ensure
equitable translation of genetic
technologies and to better
understand human history
and anthropology, we need the
breadth of human diversity to
be represented in our studies.”
These findings also show that
there is a lot more uncatalogued
genetic variation out there across
populations, including many gene
variants that may be associated
with disease, says Martin. ❚“ Some regions were rich
in heavy carbon, which is
something that we didn’t
expect to find at all”Space
Genome studies so far
haven’t covered a very wide
diversity of populationsLayal LiverpoolJEFF^ OVE
RS/GETT
Y^ IMAG
ESAncient lineages intertwined
DNA analysis of people around the world reveals a more complex human story
Tiny meteorite could
teach us how life’s
building blocks formLeah Crane