When you watch a pitcher wind up and throw a fastball down the middle, or a quarterback step out of the pocket and make a successful long pass, you’re seeing millions of years of human evolution and adaptations in action.

Or so say researchers Daniel Lieberman and Neil Roach. Their study, published today in Nature, determines that this uniquely human trait—high speed and high accuracy throwing—originated with our ancestors Homo erectus, two million years ago.

Darwin speculated that by freeing up the arms, bipedalism may have enabled our hominin ancestors to hunt effectively using projectiles. But scientists had been unable to pinpoint the exact time throwing became viable.

“When we started this research,” Roach says, “we asked: How do we do it? What is it about our body that enables this behavior, and can we identify those changes in the fossil record?”

The researchers began by creating a complex model that incorporated current research about the biomechanics of throwing. Using that model, they were able to explore how morphological changes to the body—wider shoulders, arms that are higher or lower on the body, the ability to twist the upper body independently of the hips and legs, and the anatomy of the humerus—affect throwing performance.

They also studied 20 experienced human throwers during overhand baseball pitching, demonstrating that several derived anatomical features that enable elastic energy storage and release at the shoulder are central to our ability to throw powerfully and accurately. (Video is available of these mechanics on Harvard’s website.)

“We try to push these bits of anatomy back in time, if you will, to see how that affects performance,” Roach says. “The important thing about our experiments is that they went beyond just being able to measure how the restriction affects someone’s ability to throw fast and accurately—they allowed us to figure out the underlying physics. For example, when a thrower’s velocity dropped by 10 percent, we could trace that change back to where it occurred.

“In order to test our evolutionary hypotheses, we needed to link the changes we’d seen in the fossil record to performance in terms of throwing,” he continues. “This type of analysis allowed us to do that.”

This throwing ability was incredibly important for our ancestors, the researchers say. It helped them become more successful hunters and carnivores, paving the way for a host of later adaptations, including increases in brain size and migration out of Africa.

However, while speed and accuracy proved a crucial development for early hunters, the study’s authors warn that repeated use of this motion can result in serious injuries in modern throwers, especially in young baseball players, who often suffer from laxity and tearing in the ligaments and tendons of their shoulders.

“I think it’s really a case of what we evolved to do being superseded by what we’re now asking athletes to do,” Roach says. “Athletes are overusing this capability that gave early humans an evolutionary advantage, and they’re overusing it to the point that injuries are common.”

Image: Rick Dikeman/Wikipedia

The old saying “You are what you eat” takes on new significance in the most comprehensive analysis to date of early human teeth from Africa.

Prior to about 3.5 million years ago, early humans dined almost exclusively on leaves and fruits from trees, shrubs, and herbs—similar to modern-day gorillas and chimpanzees.   However, about 3.5 million years ago, early human species like Australopithecus afarensis and Kenyanthropus platyops began to also nosh on grasses, sedges, and succulents—or on animals that ate those plants.

Evidence of this significant dietary expansion is written in the chemical make-up of our ancestors’ teeth.  These findings are reported in a series of four papers published this week in the Proceedings of the National Academy of Sciences, by an international group of scientists spread over three continents.

“These papers present the most exhaustive isotope-based studies on early human diets to date,” says the Academy’s own Zeresenay Alemseged, Senior Curator and Chair of Anthropology, and co-author on two of the papers (available here and here). “Because feeding is the most important factor determining an organism’s physiology, behavior, and its interaction with the environment, these findings will give us new insight into the evolutionary mechanisms that shaped our evolution.”

Plants can be divided into three categories based on their method of photosynthesis: C3, C4, and CAM.  C3 plants (trees, shrubs, and herbs) can be chemically distinguished from C4/CAM plants (grasses, sedges, and succulents) because the latter incorporate higher amounts of the heavier isotope carbon-13 into their tissues.  When the plants are consumed, the isotopes become incorporated into the animal’s own tissues—including the enamel of developing teeth.  Even after millions of years, scientists can measure the relative amounts of carbon-13 in teeth enamel and infer the amount of C3 vs. C4/CAM plants in an animal’s diet.

“What we have is chemical information on what our ancestors ate, which in simpler terms is like a piece of food item stuck between their teeth and preserved for millions of years,” says Alemseged.

These papers represent the first time that scientists have analyzed carbon isotope data from all early human species for which significant samples exist: 175 specimens representing 11 species, ranging from 4.4 to 1.3 million years in age.  The results show that prior to 3.5 million years ago, early humans ate almost exclusively C3 plants.  But starting about 3.5 million years ago, early humans acquired the taste for C4/CAM plants as well, even though their environments seemed to be broadly similar to their ancestors’.  The later genus Homo, including modern-day Homo sapiens, continues the trend of eating a mixture of C3 and C4/CAM plants—in fact, people who enjoy mashed potatoes with corn are practicing a 3.5 million-year-old habit.

What the studies cannot reveal is the exact identity of the food, and whether it also included animals that ate C4/CAM plants (an equally valid way to acquire carbon-13).  Possible C4/CAM-derived meals include grass seeds and roots, sedge underground stems, termites, succulents, or even small game and scavenged carcasses.  In 2010, Alemseged and his research team published the earliest evidence for meat consumption using tools, dating back to 3.4 million years ago—an additional line of evidence showing a dietary shift in human evolution.

“The change in isotopic signal documented by the new studies, coupled with the evidence for meat-eating in Australopithecus afarensis from Dikika around 3.5 million years ago, suggests an expansion in the dietary adaptation of the species,” says Alemseged.

The authors of this week’s papers also sampled fossils of giraffes, horses, and monkeys from the same environments and saw no significant change in their carbon isotope values over time—suggesting that the unique dietary transformation of early humans did not apply to other mammals on the African savanna.  The question of what drove the transformation, however, remains unresolved.

Andrew Ng is Communications Manager at the California Academy of Sciences.

Images: National Museums of Kenya. Photos by Mike Hettwer, Yang Deming