1348 21 DECEMBER 2018 • VOL 362 ISSUE 6421 sciencemag.org SCIENCEPHOTOS: (TOP TO BOTTOM) PAUL KITAGAKI JR./THE SACRAMENTO BEEVIA AP/POOL; D. GRAZHDANKIN2018 BREAKTHROUGH OF THE YEAR^ | RUNNERS-UP
This year, scientists detected molecular
traces from creatures that lived more than
half a billion years ago, sharpening their
picture of the mysterious world that gave
rise to some of Earth’s first animals and
pushing such molecular paleontology back
several hundred million years. They detected
the signatures of fat molecules in some of
the strangest fossils known, the enigmatic
life forms called the Ediacarans, and mo-
lecular evidence of sponges from long before
they appear in the fossil record.
For more than 70 years, scientists have
puzzled over the bewildering shapes of
Ediacaran fossils. Some resemble leaves or
fronds; others look like no other organisms
that have ever lived on Earth. Were the
ancient ocean dwellers plants? Animals?
Or some entirely separate form of life that
failed to survive?
Researchers at Australian National Uni-
versity in Canberra wondered whether they
could extract chemical clues from some ex-
ceptional fossils that, despite being 550 mil-
lion years old, still preserve a film of what
looks like organic material. These fossilscome from a cliff on the shore of the White
Sea in northwestern Russia, where the rocks
have escaped the heat and pressure that can
obliterate such molecular traces.Researchers first tested the idea on a
collection of small, round Ediacaran fossils
called Beltanelliformis. They removed the
film from the rock, dissolved it, and used
gas chromatography and mass spectro-
metry to look for preserved organic mol-
ecules. They found high levels of hopanes,
molecules that suggested the balls were
colonies of cyanobacteria, the research-
ers reported in January. That success gave
them the nerve to try the technique on
a fossil of a creature called Dickinsonia,
one of the most famous Ediacaran species.
Oval-shaped and about half a meter long, it
resembles a quilted bath mat. In Septem-
ber, the team reported that the Dickinsonia
fossil contained traces of cholesterol-like
molecules, a signature of animal life. That
fits with other evidence suggesting at least
some Ediacarans were among the earliest
animals on Earth.
In October, another team found traces
of molecules that today are made only by
sponges, in rock layers between 660 million
and 635 million years old. The finding sug-
gests sponges, another form of animal life,
might have evolved 100 million years earlier
than their oldest recognizable fossils.
—Gretchen VogelIn April, police announced they had arrested a suspect in one of the coldest of cold
cases: a series of rapes and murders in California in the 1970s and 1980s. It was a
stunning development, and so was the way investigators fingered the alleged Golden
State Killer. They identified his relatives by uploading a profile of DNA recovered
from one of the crime scenes to a public genealogy DNA database. Law enforcement
agencies have since used this strategy to crack about 20 other cold cases, ushering in
a new field: forensic genealogy.
Private DNA websites such as Ancestry and 23andMe contain millions of profiles
that can be used to find a person’s relatives from bits of shared DNA, but police need
a court order to search them. In the Golden State Killer case, authorities turned to a
public, no-frills online database called GEDMatch, run by two amateur genealogists
in Texas and Florida, to which anyone can submit DNA test results. Investigators
uploaded a DNA profile from a rape kit to the database, and found several distant
relatives of the perpetrator. Working with a genealogist, they then used public
records to construct large family trees and homed in on 73-year-old Joseph James
DeAngelo, whose age and location fit some of the crimes. When tests showed the
crime scene DNA matched DNA from DeAngelo’s car door handle and a discarded
tissue, they had their suspect.
This fall, geneticists reported that 60% of Americans of European descent (who
make up most ancestry site users) would have a third cousin or closer match in a
database with 1 million samples, about the size of GEDMatch. Once a database
reaches 3 million profiles, more than 90% of white individuals could be found with
similar methods—even if they have never had their DNA tested. All this has alarmed
some ethicists and geneticists who see these familial searches as an invasion of
privacy with a potential for misidentifying suspects. —Jocelyn KaiserForensic genealogy comes of age
A fossil of Dickinsonia contained traces of
cholesterol-like molecules, a signature of animal life.Joseph James DeAngelo, the alleged Golden State Killer.Molecular windows into primeval worlds
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