By THE EDITORIAL BOARD MARCH 28, 2016, New York Times
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It’s been nearly 160 years since we Homo sapiens, or “wise people,” first got an
inkling through Charles Darwin and the discovery of Neanderthal remains that
we are just another evolving species on this planet. In recent years, the pace of
new discoveries — made possible by advances in a broad array of disciplines,
including biotechnology, genetics and paleontology — has increased.
In 2010, scientists found that our ancestors not only crossed paths with
other hominids on a similar evolutionary track, but mated with them. They
discovered that modern humans interbred with Neanderthals because many
people, mostly outside of Africa, carry DNA that matches material from the
Neanderthals, our heavybrowed evolutionary relatives.
Now a new study of global genomes, published this month in the journal
Science, reports that our ancestors also crossed paths and interbred with
another distinct hominid species known as the Denisovans.
Like all the previous studies, the latest one raises at least as many
questions as it answers. It found, for example, high levels of Denisovan
ancestry in Oceania, thousands of miles from the Siberian cave where the
species was discovered less than a decade ago. Does that mean the Denisovans
wandered far and wide, or that they crossed paths somewhere else with
modern humans who later settled in Melanesia?
Another tantalizing discovery was that some regions of Neanderthal and
Denisovan DNA became more common in modern humans as generations
passed, suggesting that it proved useful for survival, perhaps by supplying
genes that bolstered immunity. But Neanderthal and Denisovan DNA was
totally absent from four regions of the modern human genome, suggesting that
there were areas in which our ancestors found better and unique evolutionary
solutions.
As discoveries and scientific methods multiply, we will become more
familiar with our distant ancestors of all kinds and species. What is already
evident is that our ancestry cannot be defined by a tidy genealogical tree, but is
an ever-evolving, mysterious and wonderfully diverse tangle of roots and
branches.
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