The Evolution Of A Special Species - NOEMA

Scientists have come to believe that the emergence of the human race involved two intertwined evolutionary processes — the evolution of our genes and of our cultures.

Credits

Lesley Newson is a research associate and Peter J. Richerson a distinguished professor emeritus in the department of environmental science and policy at the University of California, Davis. They are the authors of “A Story of Us” (Oxford 2021).

In the 1850s, on an island that would one day be part of Indonesia, a British naturalist named Alfred Russel Wallace came down with malaria. Perhaps during one of the fever dreams that are a symptom of the illness, Wallace had a profound realization: There wasn’t necessarily a supernatural force driving changes in living organisms.

Wallace had spent much of the early part of his life exploring in the tropics, observing the animals, plants and people who lived there, collecting specimens, and sending them back to England. Like most well-read English men and women of his time, Wallace was familiar with the evidence that the Earth and its life had evolved over time. Fossilized remains of strange plants and animals that no longer existed were being found all over the place. Sometimes, sea creatures were discovered embedded in rock on the tops of mountains, hundreds of miles from the coast.

Wallace had long enjoyed puzzling over the kind of force or forces that might be driving these changes. Then he realized that it could just be struggle for survival. This struggle was something Wallace witnessed all the time as he explored the tropical islands. When living things reproduced, they created far more offspring than could possibly survive, so there was constant competition. Animals competed to find food, trees competed to get their leaves into the sunlight and everything tried to avoid being food for something else.

Individual organisms were not all the same, and some had characteristics that made them better suited to their environment. They were the ones most likely to survive long enough to reproduce. If the offspring of these survivors inherit their parents’ characteristics, then the population of organisms was bound to change with each generation. The new generation would be slightly better suited to the environment than the previous one.

As soon as he was well enough, Wallace wrote to his friend Charles Darwin explaining his idea. He and Darwin had been exchanging letters for years, but Wallace didn’t know that Darwin had already had the same idea. Darwin arranged for Wallace’s letter, along with a paper of his own, to be read at a meeting of the Linnean Society of London, one of the primary organizations discussing new discoveries in natural history, in 1858.

Still in Indonesia, Wallace knew nothing of this, although he soon got letters from home telling him about the idea’s reception. He continued his exploration of the islands for another four years, returning to England in 1862 to find that everyone interested in evolution was discussing Darwin’s “Origin of Species,” which had been out for over two years.

But What About Humans?

Although Wallace agreed with Darwin about most things, his ideas about human evolution differed in an important way. Wallace believed that the evolution of the physical characteristics of living things could have come about through millions of generations of organisms competing to survive. But he couldn’t see how the consciousness and the conscience of humans could have come about in this way.

In his travels, he had seen countless examples of animals and plants competing. He had observed many times the suffering and death of creatures with an injury or illness that had made them less able to survive. A small wound or slight malaise was often fatal. But this was far less likely in the humans that Wallace had observed.

“Wallace concluded that humans don’t compete like other animals, and that this meant natural selection would not work in the same way as it did with other living things.”

During his travels in South America and Indonesia, he had met many peoples whom his friends back in Europe would call “savages.” The various tribes looked and behaved very differently from Europeans and also very differently from each other. But he found that all the humans he met were the same in an important way. In an essay he wrote for the Journal of the Anthropological Society of London, he described it like this:

In the rudest tribes, the sick are assisted at least with food; less robust health and vigor than the average does not entail death. Neither does the want of perfect limbs or other organs produce the same effects as among animals. Some division of labor takes place; the swiftest hunt, the less active fish, or gather fruits; food is, to some extent, exchanged or divided. The action of natural selection is therefore checked; the weaker, the dwarfish, those of less active limbs, or less piercing eyesight, do not suffer the extreme penalty which falls upon animals so defective.

Wallace concluded that humans don’t compete like other animals and that this meant natural selection would not work in the same way as it did with other living things. He also wondered what could account for the generosity that seemed to be universal in humans and yet, he thought, completely absent in other animals. He speculated that human evolution might be different and that some other evolutionary process might be necessary to explain the development of the moral beliefs and mental life of humans. He wondered if this evolution could be occurring outside of the immediately observable physical world.

And why not? Up in Scotland, the physicist James Clerk Maxwell was demonstrating that electric and magnetic fields travel through space as invisible waves, moving at the speed of light. So much of what had been thought of as “supernatural” was becoming understood to be part of nature. There was a sense that many amazing new discoveries were just around the corner.

“Less robust health and vigor than the average does not entail death.” — Alfred Russel Wallace

In the 1860s, there was much discussion of the possibility that an invisible “spirit world” might also be part of nature. Wallace, like a number of scientists at the time, believed that if such a world did exist, the possibility of communicating with spirits should be systematically investigated. He thought that, in spirit form, the human mind might evolve separately from a physical body.

Wallace attended some séances and heard knocking alleged to be made by disembodied spirits. He spoke to his dead relatives through mediums, and he even had his photograph taken with an apparition of his dead mother. Some of the people who produced such “supernatural phenomena” later admitted that they were frauds. Even so, Wallace remained convinced that some of the communications he’d had with the spirit world were genuine.

Nowadays, Darwin is given most of the credit for developing the theory of evolution by natural selection because of the huge amount of work he did to present evidence to support the theory. Today’s scientists admire Darwin for his determination to be guided by that evidence rather than the fashionable ideas of his time. Darwin didn’t think much of the spirit world idea, but he completely agreed with Wallace that explaining human evolution presented a problem. They both believed that all living things are related and that it’s possible to compile a great family tree of life.

“Wallace speculated that some other evolutionary process might be necessary to explain the development of the moral beliefs and mental life of humans.”

Darwin saw that humans had a place on the tree, even if our species had to be put way out on a limb. It must have irritated him that popular writers of the time misquoted him as claiming that humans are descended from monkeys. Darwin put humans on the same branch of the tree as the great apes of Africa (chimpanzees and gorillas). Monkeys are more distant relatives. Their faces may look human-like, but their bodies are very different. Most of them have a tail, for example.

Darwin’s determination to base his judgments on evidence made his views about human evolution, which he published in 1871, less popular than his earlier book on the origin of species. At the time, his views were less influential than those of some other scholars. Herbert Spencer was the celebrity pundit for human evolution. Spencer wasn’t just very eloquent; he also seemed to be very sensitive to what the public wanted to hear.

Darwin disagreed with Spencer and many others who justified their countrymen’s treatment of non-Europeans with the claim that other “races” are inferior or somehow less human. Darwin argued that the physical differences between peoples are so superficial that a biologist must conclude that not only do all humans belong to the same species, but that we are all closely related. He agreed that people raised in different environments behave differently, but he argued that experiences influence behavior.

“Darwin completely agreed with Wallace that explaining human evolution presented a problem.”

There was what Darwin called a “great gap” on the ape branch of the family tree between humans on the one end and chimpanzees, gorillas and orangutans on the other. In the years since Darwin’s death, scientists have struggled to define the nature of that “gap.” It’s taken for granted that humans are much more intelligent than other animals, but what does that mean, exactly? The precise kind of intelligence that humans possess may be unique, but other animals show great ingenuity in solving the problems that are important in their own lives.

Once scientists developed tests of intellect that were better suited to the animals they were studying, or when they simply started watching animals in the wild more closely, they found them to be cleverer than they had imagined. Animals with brains much smaller than ours are good learners with amazing memories. They’re also creative. Humpback whales work together to capture schools of tiny fish by blowing out a curtain of bubbles that acts like a net of air the fish can’t swim through. Chimpanzees have the ability to work out what others know and are ignorant of — a skill psychologists sometimes refer to as “mind-reading.” It was once thought that only humans had a “theory of mind.”

And even the human generosity that Wallace described turns out not to be unique to our species. Life for other animals isn’t constant competition. Many species of animals help to look after each other’s young and share food. Some mammals happily suckle infants that are not their own.

“The precise kind of intelligence that humans possess may be unique, but other animals show great ingenuity in solving the problems that are important in their own lives.”

The Dual Inheritance — Genes And Culture

In the years that have passed since the theory of evolution by natural selection was first proposed, scientists have solved the mystery of genetic inheritance and now understand many of its mechanisms in astonishing detail. But while some mysteries have been solved, quite a few things that once seemed straightforward have been revealed to be mysterious. For example, in the 19th century, it seemed obvious how children “inherit” their parent’s language. They listen to people around them and copy the way they talk. The mystery in Darwin’s day was how a child inherited her curly hair from her mother and her shyness from her father. Today we know how information coded in the DNA directs the formation of our hair follicles, and psychologists are testing theories about how certain genes influence personality.

But there has been less progress in understanding how we acquire our endowment of learned information. For example, instead of inheriting their parents’ way of talking, children tend to pick up the dialect of their friends. Sometimes when siblings attend different schools and have different friends, they end up speaking with different accents. What goes on to make this happen?

Over the last few decades, more and more evolutionists have come to believe that Wallace’s idea of a second evolutionary process might not be so far-fetched. They don’t think that this evolution takes place in a spirit world. But we have long known that another evolutionary process profoundly impacts human lives — the evolution of our cultures.

We know that culture changes over time. It changes fast enough that we can experience cultural evolution in our own lifetimes. Our technology develops, bits of our human-built world are destroyed while other things are added, and we’re often aware that our feelings and beliefs have changed.

“Our technology develops, bits of our human-built world are destroyed while other things are added, and we’re often aware that our feelings and beliefs have changed.”

In its broadest sense, culture is the monstrously complex, swirling mass of ideas, beliefs, habits, customs, fashions and things that surround us. Our beliefs and emotions seem so personal to us, but they’re connected to what people around us do. Our minds change, sometimes without our understanding why. We can suddenly start to question something we once took for granted. It might be something trivial, like whether or not women over 30 should wear leggings, or something more profound, like whether anyone has the right to voice an opinion about what women over 30 should wear.

Some scholars have argued that “culture” is outside science’s scope — more of the spirit than the physical brain. Others point out that because science is part of culture, it’s impossible to have a “science of culture.” They argue that a person simply can’t take an objective (“scientific”) view of something that he or she is inside of and part of.

But a broader definition sees culture as just information — the vast amount of data that we access via our social networks. Cultural information is like a set of tools that we use to operate in our world. Sometimes our cultural information allows us to create or use physical tools — such as a knife or the warm clothing necessary to survive in a cold environment. But our knowledge about our environment — such as what plants are good to eat — is also an important survival tool.

“Our beliefs and emotions seem so personal to us, but they’re connected to what people around us do.”

Many of the tools our culture gives us are “social tools” that allow us to interact with one another in complex ways. Language is probably the most important social tool — it’s been used by our ancestors for tens of thousands of generations. But our culture provides us with many other social tools. We have agreed-upon rules for how to behave in “polite society,” as well as physical objects, like money, to make it easier to trade. There are drugs, like alcohol, that can make people feel more relaxed interacting with strangers, and there are weapons to use when interactions get hostile.

In the past, separate populations each had their own cultural network. Some groups lived their lives in complete isolation. But over the last few thousand years, links between populations strengthened, allowing information, goods and people to travel more easily between them. Nowadays, we have a global network and each of us has access to some parts of the network. Because people are always editing and adding data, culture is constantly changing. The change isn’t random, and neither is the way we access cultural information.

It’s impossible to make precise and reliable predictions about how people’s minds will change. Who would have thought that television programs about cooking would be so popular when people are spending less and less time cooking their own food? But there are patterns in culture. People who spend time together tend to think in similar ways and are more likely to agree on how “things” need to change. People who spend time together are culturally similar partly because we prefer to be with people who think like us, but also because spending time with people influences the way our mind changes.

“Culture provides the mental organs we use to digest and metabolize our experiences.”

But even this isn’t predictable. The ether that connects human minds and allows ideas to flow between them often seems to defy analysis. It seems as though it might as well be happening in a spirit world. Many of us know only too well that close family members often perceive aspects of the world very differently.

The thing we call “culture” is woven into our minds. It doesn’t just supply the clothes we use to decorate our bodies. It also provides the mental organs we use to digest and metabolize our experiences.

Evolving Our Capacity For Culture

Our ancestors started to develop a culture millions of years ago, long before they walked upright or used language. Our ape forbears who foraged in the trees of African forests needed to know a lot about what is edible and how to find it, just like our distant relatives, the chimps who live in African forests today. During the first three or four years of its life, a chimp sticks very close to its mother. It needs her milk and her protection, and it needs to spend many hours watching her forage so it can learn all her tricks.

One of the chimps’ cleverest foraging tricks involves making a tool so that they can “fish” for termites. These tools are long flexible probes made from grass or twigs. The chimp pushes its probe down the ventilation tunnels of termite mounds to where sentry termites are guarding the living areas. The sentries grab onto what seems to be an intruder. The chimp then carefully extracts the probe and licks off the termites still clinging to the end. Even though termite fishing produces a highly nutritious snack, many chimp groups never do it. Primatologists believe this is because they have never learned how. The knowledge isn’t part of the culture of some chimp groups.

“Evolving from apes to humans bears more than a passing resemblance to the evolution of computing over the last few decades.”

Our ape ancestors living in the African forests likely had a simple culture similar to that of chimpanzees today but, at some point in our evolution, it started to expand and complexify. How and why did this happen? It’s too simplistic to suggest that increased brain size and more sophisticated cognition alone allowed our ancestors to develop more complex culture. It’s likely also to be due to our ancestors’ groups becoming increasingly closely connected.

Evolving from apes to humans bears more than a passing resemblance to the evolution of computing over the last few decades. Since the 1990s, computers have become better and better at processing data. But the real revolution has been the development of ways to safely link computers to networks that allow them to share information, programs and processing power.  

Over millions of years, our ancestors developed increasingly efficient information-sharing links, and this allowed cultures to evolve. Chimp cultures remain simple because the only strong connection in a chimp group is the bond between a mother and her infant. Young chimps mostly learn by watching their mother because they get little opportunity to closely observe the foraging of other group members. Natural selection favors chimps who are good at getting food. They rarely share either food or foraging tricks with others in their group.

“Chimp cultures remain simple because the only strong connection in a chimp group is the bond between a mother and her infant.”

At some point in our evolution, humans ceased to be so competitive. Alfred Russel Wallace saw this in the jungles of Indonesia, reporting that among members of the “rudest” tribes, there was a division of labor: “the swiftest hunt, the less active fish, or gather fruits; food is to some extent exchanged or divided.” But Wallace was incorrect in his conclusion that the action of natural selection was checked. There was still competition. It’s just that some of it was occurring at the level of the group.

The most successful groups were those whose members got along and worked well together. This cooperation could be promoted through the culture that the members of a group shared. If people evolved beliefs, rules, child-raising customs and other cultural elements that encouraged unselfish behavior, their group would benefit, and they would benefit too. Their group would raise more children, and their genes and culture would be passed on to the next generation.

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