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a complete mitochondrial genome for
the Denisova individual. The same
approach has yielded DNA sequences
for Neandertals (SN: 3/14/09, p. 5) and
a Greenlander who lived 4,000 years ago
(SN: 3/13/10, p. 5).
The researchers compared Denisova
mitochondrial DNA with complete mitochondrial sequences from 54 people who
are living today as well as a human who
lived in Siberia about 30,000 years ago,
six Neandertals that lived more than
40,000 years ago, a modern pygmy chimpanzee and a modern common chimp.
Mitochondrial DNA from the Denisova fossil differs from that of humans
at almost twice as many chemical positions as Neandertal mitochondrial DNA
does, Krause says.
“That number of differences is good
evidence for a new hominid because
simple variation can’t account for it,”
remarks geneticist Morten Rasmussen
of the University of Copenhagen.
Assuming that maternal ancestors of
humans and chimps diverged 6 million
years ago, the researchers calculate that
a maternal ancestor common to the Denisova hominid, Neandertals and modern humans lived between 780,000 and
1. 3 million years ago. A common maternal ancestor of modern humans and
Neandertals lived more recently, an
estimated 320,000 to 620,000 years ago.
excavations in the Altai Mountains of
siberia have unearthed a number of
artifacts attributed to early humans.
Krause and Pääbo are now directing an effort to extract nuclear DNA
from the Denisova fossil. Comparisons
of Denisova, Neandertal and modern
human nuclear DNA are needed to
determine whether this new type of
hominid is a separate species and to
check for signs of interbreeding with
Neandertals or humans.
For now, the researchers refer to
the Denisova hominid as “X woman,”
although its sex remains undetermined
until nuclear DNA can be examined.
“What we can say for now is that there
Back Story | Who’s Who in the genus homo
scientists think
the homo genus
evolved 2. 3 mil-
lion years ago.
the discovery of
1.7-million-year-old
skulls in Georgia,
though, has caused
confusion about
the genus’s direct
ancestor and rela-
tionships among
homo species.
h. erectus
bones of 50-plus
h. erectus individuals
dating from 300,000
to 800,000 years
ago have been found
at sites in Java and
china.
h. heidelbergensis
evidence for this
species, dating to at
least 350,000 years
ago, comes from
across europe. Most
believe it is an ancestor of neandertals.
h. floresiensis
a partial skeleton and
other bones found on
Flores have led some
scientists to propose
this species. it may
have lived until just
17,000 years ago.
were at least three different forms of
hominids living in the Altai Mountains
around 40,000 years ago,” Pääbo says.
At that same time, some argue, a fourth
species named Homo floresiensis, better
known as hobbits, occupied the Indonesian island of Flores (SN: 5/10/08, p. 7).
In a comment published with the new
report, geneticist Terence Brown of the
University of Manchester in England
says that further ancient DNA studies will
“possibly increase the crowd of ancestors
that early modern humans met when
they traveled into Eurasia.”
Anthropologist Ian Tattersall of the
American Museum of Natural History
in Ne w York City agrees. Hominid evolu-
tion over the past 6 million to 7 million
years includes at least two dozen species,
in his view. It was “practically routine”
for species to live in the same area at the
same time, he says.
In contrast, anthropologist Erik
Trinkaus of Washington University in
St. Louis views the new genetic data
with skepticism. “I don’t know what to
make of this, at least not until there is
more substantial fossil material than a
partial finger bone,” he says. “It may be
going too far to propose a new hominid.”
Trinkaus, who sees fewer hominid species than Tattersall, cautions that biologists have trouble identifying different
species even among living primates.
top: J. Krause; bacK story: h. floresiensis: Mauricio anton/photo researchers, inc.;
all others: Maurice Wilson/©the natural history MuseuM, london
h. neanderthalensis
after their ancestors
left africa, neandertals spread across
europe, the Middle
east and into siberia
before going extinct
30,000 years ago.
h. sapiens
Modern humans are
the only living members of the homo
genus. they may
have lived near other
hominids 40,000
years ago.
