RESEARCHERS say they have
found the ancestral homeland of
our species in Africa, but the claim
has provoked deep scepticism.
Genetic evidence was used to
pinpoint an area in north-east
Botswana as the spot where our
species first emerged. However,
other scientists say the methods
deployed are flawed.
The new study is the latest to try
to resolve a long-standing puzzle:
while there is overwhelming
evidence that our species evolved
in Africa, it is unclear where.
Eastern and southern Africa
have yielded the most fossils,
so both have been claimed as
our homeland at various points.
However, because fossils
have been found elsewhere in
Africa, many anthropologists
have recently concluded that
interbreeding populations existed
all over the continent, and hence
there is no single homeland.
The new study disputes this.
It was led by Vanessa Hayes of
the Garvan Institute of Medical
Research in Sydney, Australia. She
and her team gathered more than
1200 samples of mitochondrialDNA from people in southern
Africa. The researchers used this
to create a family tree showing
when ancient populations split.
They concluded that the oldest
lineage emerged about 200,
years ago, which they interpret
as the origin of our species.
The team found little evidence
of mixing between groups, so
concluded that populations have
probably not moved much sincethey were established. Based on
where the oldest variants are
found today, they argue that our
species’ homeland was a vast
wetland called Makgadikgadi-
Okavango in Botswana (Nature,
doi.org/dc9p). Today, much of that
area is a salt pan, although the
Okavango delta floods seasonally
and becomes rich in wildlife.
The researchers suggest that
humans only spread beyond
Makgadikgadi-Okavango when
the climate changed. In support
of this, team member Axel
Timmermann at the Institutefor Basic Science in Busan, South
Korea, has shown that changes
in Earth’s orbit over the past
200,000 years would have shifted
Africa’s rain belts, opening green
corridors from Makgadikgadi-
Okavango to other parts of Africa.
These changes seem to coincide
with population splits revealed
by the DNA: 130,000 years ago,
a small group broke away to the
north-east, for instance.
It is a compelling story, but
experts in human prehistory
aren’t impressed. The problem
is that mitochondrial DNA
can’t tell us about such ancient
populations, says geneticist Mark
Thomas of University College
London. Mitochondrial variants
map only weakly onto individual
populations, and this mapping
gets worse further back in time.
The paper also ignores evidence
that our species is more than
200,000 years old, says Eleanor
Scerri at the Max Planck Institute
for the Science of Human History
in Jena, Germany. For instance,
Moroccan fossils described in a
2017 study suggest that our species
is at least 315,000 years old. ❚10 | New Scientist | 2 November 2019
“Satellites can mistake
rooftops for the ground, so
high-rise cities can seem to
be at low risk of flooding”Human evolutionMichael MarshallALAMYNews
Botswana’s Okavango
delta has been pegged as
our ancestral homeClimate changeUP TO 630 million people are living
on land threatened by flooding
from sea level rises by the end of
the century – three times the
number previously thought at risk.
The greatest increase, according
to a new analysis, is in Asian
megacities. This is due to the way
earlier estimates were worked out.
“To us, it’s a staggering
difference. It’s a completely new
perspective on the scale of thisthreat,” says Benjamin Strauss at
Climate Central, an independent
organisation in the US highlighting
climate change. He led the analysis.
Previous calculations of the
flood risk have been based on
estimates of land elevation using
satellite data. But that approach
gets confused by rooftops and
forests, which can be mistaken for
the ground, meaning a skyscraper-
packed city, such as Shanghai, could
misleadingly be deemed to be at
a low risk of flooding as seas rise.
Strauss and his team used
artificial intelligence to train a
computer model on several sets ofdata, including much more accurate
maps of elevation in the US.
The model predicted where the
old information was mistaken and
tried to correct the errors caused by
buildings and trees, to reassess the
vulnerability of cities.
The results suggest there are far
more people living on land that is
at risk today: about 250 million
versus estimates made using the
old data of up to 65 million. Asglobal warming causes sea levels
to rise, that figure jumps to as many
as 630 million by 2100, assuming
a future in which greenhouse gas
emission rises are high (Nature
Communications, DOI: 10.1038/
s41467-019-12808-z).
Asia is likely to be far more
vulnerable to sea level rise than
we thought, because the region’s
high-rise coastal cities appeared
as elevated ground in satellite data.
“I think that coastal cities that
want to thrive into the [future] need
to take a very close look at their
vulnerability,” says Strauss. ❚
Adam VaughanHave we finally discovered the
birthplace of modern humanity?
Many more
cities at mercy
of rising seas