The Big Ratchet: How Humanity Thrives in the Face of Natural Crisis (7 page)

Back in England, years went by with no news of Sir John’s expedition. Lady Jane Franklin, Sir John’s wife, had commissioned many voyages to rescue
her missing husband. After several unsuccessful attempts, explorer Francis McClintock set sail in 1857 and finally solved the mystery. Captain McClintock returned with relics of tin cans and old clothes, stories from the Inuit about the demise of the crew as they trudged across the ice, and a written record of the journey retrieved from King William Island with the date of Franklin’s death.

McClintock narrated the details of his search expedition to the Royal Geographical Society on November 14, 1859, more than fourteen years from the time Franklin had set sail with his crew. In his report, McClintock repudiated Franklin’s earlier, overly confident claim, telling the gathering that it is “evidently an error to suppose that where an Esquimaux can live, a civilized man
can live there also.” With that, a chapter closed on Britain’s thwarted quest to sail across the northern Atlantic through an ice-free passage.

My intent in relaying Franklin’s catastrophe is not to retell a well-known story or to dwell on the foibles of the brave explorers. Rather, it is to point to the key ingredient that makes our species different from others. Franklin’s crew and the Inuit belonged to the same species. But the shared ancestry did not provide Franklin and his crew with knowledge of survival tactics in the Arctic—how to hunt, build kayaks, and cooperate with the group to get through the winter. Nor did their parents and communities teach them these skills as they grew up in England.

It’s no surprise that the British explorers lacked the right skills. The Inuit and British cultures were each built on an accumulation of knowledge passed from one generation to the next. Each culture fit the local surroundings. Culture—shared knowledge accumulated from experience—takes time and builds over generations. Franklin’s crew and the Inuit could not readily swap places, and a few years were not long enough for the unfortunate men to learn what the Inuit culture knew before starvation snatched away the chance. Given a longer time, more expeditions, a larger crew, or even more contact with the Inuit, perhaps they could have learned to adapt to the harsh Arctic conditions. For the Inuit, it took millennia of struggle to learn to survive in the severe climate.

The prominent role of culture in human evolution has stumped the minds of many, including Charles Darwin. Darwin understood that his theory of natural selection would not stand up to scrutiny if he tried to argue that humans were an exception to the general rule. The theory explained what he had seen on the Galapagos Islands in 1835, where the distinct shapes and sizes of the finches had intrigued him as a young naturalist. It was simple and elegant, as it remains to this day. After ancestral finches arrived on the island from the South American mainland, some ate seeds and some ate insects. Those with blunt, strong beaks were more likely to survive by crunching seeds from the ground. Those with sharp, pointed beaks were more likely to survive by grasping insects on trees. Surviving ground-birds passed on blunt beaks to their offspring, and tree-dwelling birds passed on pointed beaks. Over time,
ground finches and tree finches diverged into separate species. Inherited genes responding to the environment set the pace for evolution.

But Darwin struggled to explain how human culture—ideas that boost our species’ success as they pass from one generation to the next and from one place to another—fit within his theory of natural selection. In his famous 1874 treatise
The Descent of Man
, he hinted at the notion that the powerful force of natural selection weakens as human culture becomes more complex. “With highly civilized nations, continued progress depends in a subordinate degree on natural selection,” he wrote. “The more efficient causes of progress seem to consist of a good education during youth while the brain is impressible, and of a high standard of excellence, inculcated by the ablest and best men, embodied in the laws, customs, and traditions of the nation, and
enforced by public opinion.”

Three-quarters of a century later, the Russian biologist Theodosius Dobzhansky and British American anthropologist Ashley Montagu picked up the question of how human culture evolves, concluding that “instead of having his responses genetically fixed as in other animal species, man is a species that invents its own responses, and it is out of this unique ability to invent, to improvise his responses that
his cultures are born.” Despite the interest of Darwin, Dobzhansky, and Montagu in the subject, today only a small number of anthropologists, biologists, and psychologists devote their careers to intriguing and thorny questions about the forces that shape the evolution of human culture. Among them are Peter Richerson and Robert Boyd, who rely on modern mathematical models and laboratory experiments to piece together the puzzle of how genes and culture intertwine and coevolve. Their goal is to explain why humans, rather than our chimp or bonobo cousins, have the extraordinary ingenuity to dominate the world.

Culture enabled the Inuit to adapt to the harsh Arctic environment through customs, traditions, and socially accepted norms. Culture
explains the different fates of Franklin’s crew and the Inuit in those long, dark winters. How culture evolved and shaped our species’ destiny might be one of the most fascinating unresolved puzzles of human history. As Richerson and Boyd put it, “culture would never have evolved unless it could do
things that genes can’t!”

From Genes to Ingenuity

Communication. Sharing information. Transmitting knowledge. These tools constitute the lifeblood of all cultures and the foundation for all life. When ancient forms of life acquired the machinery to store DNA and pass their genes to their offspring, they secured a means to transmit information to the next generation about how to survive in the environment. Through inheritance of genes, parents could “tell” their children what traits they had used to survive. Parents could communicate their success.

All life, including humans and the other great apes, employ early life’s great invention, transmitting information from one generation to the next through genetic inheritance. The cost of passing on genes is minimal to the parents, and the savings to offspring are large. Offspring need not invest time or energy to learn everything about their environment. The information is hard-wired. So long as the environment doesn’t change so rapidly that the information becomes invalid, the hard-wired communication strategy of genetic inheritance beats out all others. Many species whose life-spans are short compared with the time scale of changes in their environment rely exclusively on this strategy, from those as simple as viruses to those as complicated as flies.

But genetic inheritance is not foolproof. Unusually heavy rains hit the Galapagos Islands in the early 1980s. The rains produced abundant seeds for the finches, but favored the plants that produced small, soft seeds over those that produced large, hard ones. Finch species that
fed on large seeds were at a disadvantage, and their numbers dwindled. Those individuals who did survive had smaller beaks than was the norm for their species. The large-beaked finches were out of luck. They were locked into the
beak size they’d inherited from their parents.

The ability to learn can compensate for the problem of locked-in inheritance. Brain power is the key ingredient. By inheriting an intelligent brain, rather than just a specific trait, such as beak size, offspring stand a better chance of finding adequate food even if the usual source is for some reason lacking. Finches that could learn would be able to figure out how to crunch seeds of various sizes by themselves and wouldn’t have to rely on mom’s or dad’s genes for the right beak size in order to find food. The species would be able to adapt to a changing condition faster than is possible through natural selection, and perhaps could avoid a disastrous die-off in a particularly bad year.

Humans are far from the only species with intelligent brains that can learn how to find food, choose mates, and stay out of danger. Rats learn to navigate through mazes. Elephants quickly learned to cooperate in an experiment in which they could only get food if one elephant on each end
pulled a rope. American crows can learn how to recognize the faces of the people who trap them and scold the enemy
with a harsh “kaw.” Most learning in other species occurs through a repeated process of trial and error. The trial-and-error strategy provides a way to escape the dangers of locked-in behaviors, but it has its own downsides. Errors have costs. If an adventurous finch eats a poisonous seed or can’t manage to find food, the consequences are disastrous. Moreover, learning requires a big, complex brain that consumes a lot of energy from food. The benefit might
not be worth the investment. Mathematical models contrasting the costs and benefits of genetic inheritance versus trial-and-error learning show that the benefits of learning outweigh the costs only when the environment changes rapidly compared with the
life-span of the animal.

Of course, not all learning is through trial and error. Learning from peers and parents can speed up the process. Consider the Japanese macaque, with its thick fur and red, gruff face. In the 1950s, Japanese researchers were struck by the
macaque’s complex social behavior. In hopes of studying this behavior, the researchers enticed the shy animals with sweet potatoes, wheat, and soybeans. A few years later, a young female macaque named Imo took the sandy potatoes and began to wash them in a nearby stream. Over the course of the next few years, other macaques followed suit, until the practice became widespread in the group. The macaques were clearly learning from each other, although it remains unclear whether they were imitating the act of washing the potatoes or figuring out how to wash potatoes through trial and error once they got the idea. Scientists studying behavior in the intervening decades reveal similar social learning in many species, from guppies learning swimming routes from their peers to bottlenose dolphin mothers teaching their calves to encircle a school of
fish for their next meal.

Like the simpler communication strategies—genetic inheritance and individual learning with trial and error—social learning has its
pros and cons. It’s a great way to spread ideas quickly about how to collect food or avoid danger. If each individual had to invent each skill from scratch, complicated behaviors like washing potatoes would be much less common. Imagine each bottlenose dolphin calf figuring out how to hunt de novo by trial and error. It would take a long time, if it occurred at all. The calf would be far less successful in catching its fish than those capable of social learning. Social learning also means that animals can get information not just from their parents, as with genetic inheritance, but also from their peers. The upside of learning from peers is that new ideas can spread rapidly. The downside is that the behavior might actually not be such a good idea after all, more on the side of an error in the trial-and-error process. Just ask a parent lying awake at night worrying that an offspring will pick up smoking, drugs, and other dangerous behaviors from peers.

The mathematical models have a simulated answer to the costs and benefits of social learning. When variability in the environment is on the order of tens or hundreds of generations, somewhere between the very slowly changing environment for genetic inheritance and the rapidly fluctuating environment for individual learning, then social learning is the most advantageous strategy. If the variability is too fast, there’s no point in learning from the previous generation. With too little variability, genetic inheritance does the job of communicating information just as well without the need to devote energy to building and maintaining brains large enough to learn. But in between these extremes, social learning gives a species the flexibility to learn rapidly from those with recent experience, whether it’s a parent, a neighbor, or a clever acquaintance.

Humans are masters at social learning. Brains that are distinctively large for our body size, with a complex structure to
process information, make it possible. Scientists point to multiple reasons why evolution might have followed that path. Some scientists contend that humans
evolved to be such excellent social learners due to the Goldilocks-like, just-right amount of climate fluctuations in the prehistoric past. The Pleistocene waxing and waning of the Ice Ages during the past few hundreds of thousands of years may have created the variability in warm and cold or wet and dry conditions that altered what food was available for our early human ancestors and where they could find it. Brain power that provided flexibility for learning could have given these ancestors an edge in adapting to the fluctuating climate. More than half the increase in brain size occurred during the
climatically noisy Pleistocene.

Most probably, many forces
interacted at different times. Energy-sucking larger brains could have evolved in tandem with our relatively short digestive tracts. As humans gained the ability to control fire, cooked meat and other foods became possible. Cooked foods were more nutritious than raw foods, took less time to chew, and were easier to digest. The surface area of a human stomach evolved to become less than one-third that of other mammals of the same weight, which means
less energy gets consumed in the process of digestion. More calories from food could then go to the brain than to digestion. The need for memory, planning, and communication by creatures that hunt and cooperate in large social groups could have nudged evolution toward developing our shorter
digestive tracts and large, learning brains.