Of all living things, why do humans alone create advanced technology? Not long ago, scientists thought it was because we are the only intelligent life form on this planet. That explanation no longer suffices. Over the last decade, scientists have found that crows can use tools, hyenas can solve complex problems, jays can plan for the future, rats and voles can show empathy, and ducklings are capable of abstract thought.
Yet our technology is extraordinary. Why were we the ones to transform the planet? A clue comes from a recent paper on a genetic change that helped our ancient ancestors tolerate smoke after fire was invented. It is the latest finding to bolster the notion that natural selection acts on our species in a unique way. While evolution forces all living things to adapt to changing natural environments, this emerging school of thought holds, it also forces humans to adapt to our own inventions. And indeed, there is evidence we have been physically reshaped by agriculture, dairy farming, stone tools, spears and the taming of fire.
In the paper linking the taming of fire to biological evolution, published earlier this month in the journal Molecular Biology And Evolution, scientists identified a genetic mutation that allows us to better break down the most toxic chemicals that make up wood smoke. The authors showed that all present-day humans carry this mutation, which is not present in any other animal. By scraping DNA from ancient skeletons, scientists found that the mutation was present in the 45,000- year-old bones of a human ancestor. They also found that Neanderthals lacked this mutation. Why didn't they get it? Bad luck. In the game of evolution, new versions of genes may spread because they endow individuals with a survival or reproductive advantage, but the changes appear through random chance.
The Neanderthal version of the gene was not necessarily deadly, but the study's lead author, Pennsylvania State University's Gary Perdew, describes it as a risk factor. Regular inhalation of smoke can weaken the immune system, he says, making people more vulnerable to diseases. There is no way to know if this contributed to the Neanderthals dying out - but it may well have helped our lineage to thrive.
Similar examples abound. In his 2015 book, The Secret Of Our Success: How Culture Is Driving Human Evolution, Domesticating Our Species, And Making Us Smarter, Harvard anthropologist Joseph Henrich observed that the invention of milking animals would have pushed the spread of genes that allowed people to digest lactose. But before that gene spread, some communities invented cheese and yogurt, which are much lower in lactose. Those inventions, in turn, may have dampened the spread of lactose tolerance.
Another example: Scientists suspect that genes allowing us to metabolise alcohol arose some 10 million years ago, when apes descended from the trees and feasted on partially fermented fruit. But Professor Henrich proposes that the invention of rice wine in Asia prompted the spread of another genetic variant - one that causes people to become nauseous and flushed if they drink more than a small amount - thus protecting them from the perils of excess.
Similarly, in 2013, Harvard anthropologist Daniel Lieberman and his colleagues demonstrated a connection between the invention of the spear and the human ability to throw. "We are the only species capable of throwing hard and fast and accurately at the same time," he said. In another recent paper, Professor Lieberman and his colleagues argued that the invention of stone tools to cut up meat allowed human teeth and jaws to shrink, perhaps allowing them to become better adapted for talking.
Some people argue that evolution has stopped, Prof Lieberman said, because technology allows us to adapt to dietary and climate changes and new diseases without the help of natural selection. But that is wrong, he said. Technology has been driving evolution for a long time, and there is no reason that facet of it will stop.
The interplay between cultural and genetic changes represents what Prof Henrich calls a major biological transition, turning us into "a new kind of animal". What makes us special is the advanced state of our cultural development intertwined with our biological evolution. In other words, when humans invent technology, we also reinvent ourselves.