Is Stephen Hawking Right About Hostile Aliens?

SETI's Allen Telescope Array — The SETI Institute's Allen Telescope Array (ATA) is hunting for radio signals from hypothetical intelligent alien life in our galaxy.

(Image credit: SETI Institute)

E.T. was the perfect extraterrestrial: Cute, smart and — best of all — a perfect pacifist.

Unfortunately, scientists aren't so sure that an actual intelligent alien would be so benign. In a recent interview with El País, famed physicist Stephen Hawking posited that an alien visitation would put Earthlings in the same position as Native Americans when Columbus landed on their shores.

Latest Videos From

Watch full video here:

No one really knows how humans got to be so clever. What's clear is that hominin brains began expanding wildly about 2 million years ago. (Hominins include those species after the human lineage — the genus Homo — split from the chimpanzee lineage.) By around 100,000 years ago, humans made the never-before-seen leap to inventing language. And by at least 40,000 years ago, our ancestors were making art.

Many anthropologists and evolutionary biologists have tried to pinpoint the special circumstances that make these huge brains worth the expense. Charles Darwin suggested that perhaps males developed cleverness to attract females, much as a male peacock developed showy tail feathers to prove to potential mates that he could strut his stuff. But if brains were just for sexual display, scientists would expect to see big differences between male and female intelligence — females, not having to attract mates, shouldn't waste so much effort on their brains, much as peahens don't waste effort on growing shiny feathers (theirs are dull and brown). And female humans are just as smart as males.

Humans have done the same, and researchers can't quite figure out why. The brain could have evolved to allow humans to use tools, but chimpanzees use tools without developing complex languages, art and culture. One provocative theory holds that pathogens play a role: The brain is vulnerable to infection, wrote Hungarian researcher Lajos Rózsa in a 2008 article in the journal Medical Hypotheses. Showing off one's cleverness may be a way of showing off how resistant one is to infection. After all, if you're smart enough to invent language and art, you must be pretty good at battling brain parasites.

The ecological dominance-social competition hypothesis works like this: Human ancestors reached a point in which their interactions with one another were the most important factor in whether they'd survive and pass on their genes. Finding food and shelter was still important, Flinn said, but it wasn't the main factor determining evolutionary success. The difference between clever humans and, say, caribou, is that intraspecies relationships drove evolution the fastest in humans, Flinn said. A herd of caribou has social interactions, to be sure: Males have to fight for mates, for example. But a more pressing concern would be avoiding predators and finding food. For hominins, these external issues became relatively less important, the theory goes, while their ability to form coalitions, to have empathy and to behave in such a way as to win friendships from others became key to their survival. [10 Things That Make Humans Special]

Environmental factors may determine whether a mate-or-die system emerges. For example, chimpanzees are a particularly homicidal (chimpacidal?) species, Carrier said. Work by primatologist Richard Wrangham at Harvard University and colleagues finds that chimp "wars" arise from a chimpanzee's territorialism. Small groups of foraging chimps may come into contact with other chimpanzees; killing these competitors (particularly when the foragers have numbers on their side) can be beneficial by opening up access to more resources.

Deadly male-male competition is less of a way of life for bonobos, humankind's other closest primate ancestor. Male bonobos stick by their mothers and the species is less territorial than chimpanzees. Bonobo foraging groups are also larger, perhaps because their food sources are more abundant, studies have found. Would aliens act more like bonobos or chimps? Hard to say. Researchers are even split on whether humans are more inherently aggressive or inherently peaceful.

A controversial theory holds that aggression was a driving force in human evolution. The "Killer Ape" hypothesis argues that the human ancestors who thrived were those better adapted for fighting. For example, Carrier said, modern humans can form fists, which our closest primate relatives cannot. This particular hand configuration may have evolved primarily for better manual dexterity — but it also could have come in handy as a club. Likewise, when human ancestors started walking on two legs, their face bones also evolved to be stronger and less delicate. This could be due to diet, Carrier said, but male face bones are more robust than female face bones, a sign that male-male competition could be at play. In other words, thick facial bones could be a defense against the fist, a weapon that would have become available once human ancestors became bipedal.

Stephanie Pappas is a contributing writer for Live Science, covering topics ranging from geoscience to archaeology to the human brain and behavior. She was previously a senior writer for Live Science but is now a freelancer based in Denver, Colorado, and regularly contributes to Scientific American and The Monitor, the monthly magazine of the American Psychological Association. Stephanie received a bachelor's degree in psychology from the University of South Carolina and a graduate certificate in science communication from the University of California, Santa Cruz.