This essay is adapted from the newly released book, “A History of the Human Brain: From the Sea Sponge to CRISPR, How Our Brain Evolved.”
Courtesy Dr. Bret Stetka
“He was a bold man that first ate an oyster.” – Jonathan Swift
That man or, just as likely, that woman, may have done so out of necessity. It was either eat this glistening, gray blob of briny goo or perish.
Courtesy Dr. Bret Stetka
Dr. Bret Stetka
Beginning 190,000 years ago, a glacial age we identify today as Marine Isotope Stage 6, or MIS6, had set in, cooling and drying out much of the planet. There was widespread drought, leaving the African plains a harsher, more barren substrate for survival – an arena of competition, desperation, and starvation for many species, including ours. Some estimates have the sapiens population dipping to just a few hundred people during MIS6. Like other apes today, we were an endangered species. But through some nexus of intelligence, ecological exploitation, and luck, we managed. Anthropologists argue over what part of Africa would’ve been hospitable enough to rescue sapiens from Darwinian oblivion. Arizona State University archaeologist Curtis Marean, PhD, believes the continent’s southern shore is a good candidate.
For 2 decades, Dr. Marean has overseen excavations at a site called Pinnacle Point on the South African coast. The region has over 9,000 plant species, including the world’s most diverse population of geophytes, plants with underground energy-storage organs such as bulbs, tubers, and rhizomes. These subterranean stores are rich in calories and carbohydrates, and, by virtue of being buried, are protected from most other species (save the occasional tool-wielding chimpanzee). They are also adapted to cold climates and, when cooked, easily digested. All in all, a coup for hunter-gatherers.
The other enticement at Pinnacle Point could be found with a few easy steps toward the sea. Mollusks. Geological samples from MIS6 show South Africa’s shores were packed with mussels, oysters, clams, and a variety of sea snails. We almost certainly turned to them for nutrition.
Dr. Marean’s research suggests that, sometime around 160,000 years ago, at least one group of sapiens began supplementing their terrestrial diet by exploiting the region’s rich shellfish beds. This is the oldest evidence to date of humans consistently feasting on seafood – easy, predictable, immobile calories. No hunting required. As inland Africa dried up, learning to shuck mussels and oysters was a key adaptation to coastal living, one that supported our later migration out of the continent.
Dr. Marean believes the change in behavior was possible thanks to our already keen brains, which supported an ability to track tides, especially spring tides. Spring tides occur twice a month with each new and full moon and result in the greatest difference between high and low tidewaters. The people of Pinnacle Point learned to exploit this cycle. “By tracking tides, we would have had easy, reliable access to high-quality proteins and fats from shellfish every 2 weeks as the ocean receded,” he says. “Whereas you can’t rely on land animals to always be in the same place at the same time.” Work by Jan De Vynck, PhD, a professor at Nelson Mandela University in South Africa, supports this idea, showing that foraging shellfish beds under optimal tidal conditions can yield a staggering 3,500 calories per hour!
“I don’t know if we owe our existence to seafood, but it was certainly important for the population [that Dr.] Curtis studies. That place is full of mussels,” said Ian Tattersall, PhD, curator emeritus with the American Museum of Natural History in New York.
“And I like the idea that during a population bottleneck we got creative and learned how to focus on marine resources.” Innovations, Dr. Tattersall explained, typically occur in small, fixed populations. Large populations have too much genetic inertia to support radical innovation; the status quo is enough to survive. “If you’re looking for evolutionary innovation, you have to look at smaller groups.”
MIS6 wasn’t the only near-extinction in our past. During the Pleistocene epoch, roughly 2.5 million to 12,000 years ago, humans tended to maintain a small population, hovering around a million and later growing to maybe 8 million at most. Periodically, our numbers dipped as climate shifts, natural disasters, and food shortages brought us dangerously close to extinction. Modern humans are descended from the hearty survivors of these bottlenecks.
One especially dire stretch occurred around 1 million years ago. Our effective population (the number of breeding individuals) shriveled to around 18,000, smaller than that of other apes at the time. Worse, our genetic diversity – the insurance policy on evolutionary success and the ability to adapt – plummeted. A similar near extinction may have occurred around 75,000 years ago, the result of a massive volcanic eruption in Sumatra.
Our smarts and adaptability helped us endure these tough times – omnivorism helped us weather scarcity.