Half a million years ago in South Africa early human ancestors shaped lumps of rock into lethal points and then attached them to wooden shafts, producing the earliest known stone-tipped spears. It took a lot more time and effort to make these multicomponent implements than to make a simple, untipped wooden spear, but the result was a deadlier means of dispatching prey. That’s what many archaeologists have assumed anyway. Few have put that claim to the test, however.

To that end, Jayne Wilkins of Arizona State University and her colleagues recently conducted a controlled experiment aimed at gauging the efficacy of wooden spears and stone-tipped spears. They focused on hand-delivered spear technology, as opposed to high-velocity projectile technology such as arrows, which were invented much later. Using a calibrated crossbow to simulate spear thrusting, the investigators plunged replicas of the two types of weapons into ballistics gelatin, a substance that is similar in density to the muscle tissue of humans and other animals and that is typically used to show how modern ballistic weapons damage flesh. They then measured the penetration depth and the size and shape of the gelatin “wounds.”

The team found that both types of spears penetrated to about the same depth. The stone-tipped spears delivered significantly larger internal wounds, however, creating cavities that were nearly 25 percent larger than those left by the untipped spears.

“A larger wound track translates to more tissue damage, an increased probability of hitting the heart, lungs, and/or major blood vessels, and an increased probability of incapacitating prey,” the researchers explain in a paper published on August 27 in PLOS ONE. That boost in destructiveness would have provided a safer, more reliable way of bringing home the bacon. And enhanced access to meat, the authors say, would have had far reaching effects on our ancient ancestors:

“Regular use of this new technology could have reduced adult mortality, increased average lifespan, increased daily return rates of large, high-quality food packages, and decreased daily nutritional variance. These effects may have changed the amount and regularity of resources adults can contribute to dependents, with important implications for human life history. An increased juvenile period, higher female fertility, and pair-bonded cooperative breeding all may be explained in part by higher rates and reduced variability in successful resource capture among hunter-gatherers.”

Moreover, the technology could have changed the way early humans interacted, both with members of their own social groups as well as members of other groups:

“Computer simulations suggest that weapon use may be linked to human cooperation. Agents with extra-somatic weapons are more likely to cooperate with each other than agents without extra-somatic weapons, in part because of the increased risk of lethality when agents choose to defect.”

Amazing, isn’t it, how such a seemingly simple invention may have transformed humankind.



How Hunting Made Us Human

Scientific American Single-Topic Issue on Human Evolution (2014)