The Next Species: The Future of Evolution in the Aftermath of Man

by Michael Tennesen

  To arrive at this figure, Harpending and Cochran analyzed data from the International HapMap Project, an effort to describe the common patterns of genetic variation in the human genome with a goal of uncovering the genetic roots of complex diseases. The project gathered results from eleven different populations around the world, spotlighting evidence from specific sites in the human genome that influenced gene expression.

  “We can compute the average amount of change in the human genome and it’s one hundred times faster,” says Harpending. “Which make sense. There’s one hundred times as many people, and that creates one hundred times as many targets for genetic mutations.”

  As genes develop, so do mutations, which are genes that don’t look or act as they did before. Most of these mutations are discarded in favor of the standard set, but once in a while a favorable genetic mutation occurs, with the result that people with the mutation have more children, are better adapted to fight off disease, or simply live longer. Such mutations offer an advantage: their owners do better and are more likely to survive. When this happens, the mutation is selected for and is passed on to future generations. Harpending and Cochran looked for these types of favored mutations in the human genome in regions of unshuffled genes, which indicate recent selection, since nature regularly reshuffles its genes.

  These favorable genetic mutations have helped man in different ways. Man living at higher altitudes had to adapt to less oxygen in the air. To accomplish this, Andeans developed barrel chests and blood that held more oxygen, while Tibetans developed faster breathing to take in more oxygen. Scientists from the Beijing Genomics Institute recently found a set of genes in Tibetans that have helped them adapt to low oxygen levels. These “new” genes were only three thousand years old.

  Harpending and Cochran also found that 7 percent of human genes underwent evolution as recently as five thousand years ago. And a lot can happen in five thousand years. Darwin chose domestic animals to illustrate much of his On the Origin of Species. Dogs come in enormously varied shapes and sizes. Take, for instance, a Chihuahua, which averages 7 pounds (3.2 kilograms), and a Great Dane, which averages 115 pounds (53 kilograms). Both come from the same ancestor. Neither of them looks like a wolf, yet most breeds of dog were derived from wolves in the last two hundred years.

  Man is also changing. The last ten thousand years have seen numerous genetic changes to human bones and teeth along with the rapid evolution of our diet and our adaptions to disease. We are taller. Our life expectancy is much greater. Changes in society have led to evolutionary adaptations. Harpending says that we are getting less alike, so that we are not merging into a single mainstream human type. We are not the same humans we were one thousand or two thousand years ago. This may account for part of the differences between the Viking invaders and their peaceful Swedish descendants.

  Harpending’s coauthor, Cochran, says: “History looks more and more like a science fiction novel in which mutants repeatedly arose and displaced normal humans—sometimes quietly, by surviving starvation better, sometimes as a conquering horde. And we are those mutants.”

  As Homo sapiens migrated into Eurasia, evolution produced changes in skin color and adaptations to cold. Some of the biggest changes came with the transition to agriculture. Larger populations and more dense living conditions promoted virulent epidemic diseases like cholera, typhus, yellow fever, malaria, and smallpox. But over time this led to the development of some genetic resistance to those diseases.

  Neanderthals, a species that developed in Europe, had adaptations to climate that other Homo species never developed in Africa. As we have discussed, resistance to such diseases as malaria is far more prevalent in Central Africans than Northern Europeans. Skin color is another important adaption to environment. Monkeys and other primates have pale skins under their fur, but humans that lost their fur, perhaps to sweat more freely, evolved darker skins to protect against ultraviolet light. The process reversed itself when man first ventured northward, where his skin grew lighter, maybe to better synthesize vitamin D.

  Peter Grant at Princeton University worked on the Galápagos Islands and likes to lecture his students about the persistence of evolution, claiming that evolution is always happening. Genes of this generation are not the same as the last. Nor will they be the same in the next. He claims it’s a mathematical certainty. Genes keep changing. You may not notice it. The trees around you may look the same. And the birds and the squirrels may look similar year after year. “They aren’t,” Grant said in an interview with author Jonathan Weiner for The Beak of the Finch: A Story of Evolution in Our Time. “They’re different. But you can’t see it, the differences are too subtle.”

  Evolutionary changes are proceeding at a genetic level, and sometimes they are heritable and apparent—the difference in height and longevity between you and your grandparents—but most times they are not.

  One of the most game-changing mutations to the human genome was lactose tolerance. It enabled man to digest milk beyond infancy. It is responsible for the largest human expansion in history, that of the Indo-European language family.

  The term “Indo-European” refers to the family of related languages that spread over western Eurasia, the Americas, and Australia. It includes Spanish, English, Hindi, Portuguese, Russian, German, Marathi, French, and numerous other languages and dialects. Today there are over three billion native speakers, close to half the human population on earth.

  The idea of a single large linguistic family first arose from similar observations of people from England and people from India. Sir William Jones, the chief justice of India, mentioned these similarities in a lecture in 1786, and scholars began to trace its history through linguistics and archaeology. The first or Proto-Indo-Europeans raised cattle, sheep, and goats. They were warriors, the young men gathering into brotherhoods with challenging initiation rites.

  They appeared about five thousand years ago, perhaps where modern Turkey is or in the grasslands farther north. They raised stock and grew grain but depended more on animal husbandry than on farming. They expanded their dominions, it is thought, by military conquests driven by the domestication of the horse but also by the genetic mutation that gave them lactose tolerance.

  Indo-Europeans originally used cattle to pull their plows and wagons, but also to provide humans with beef and leather. But as lactose tolerance spread, more people began to keep their cattle for milk rather than meat. This was a major advantage, because dairy farming is much more efficient than raising cattle for slaughter—dairy producing about five times as many calories per acre of land.

  Proto-Indo-Europeans were perhaps the most competitive in areas less ideal for growing grain. It was thus easier to tend dairy cattle year-round than to try to grow grain. As dairymen, they were more mobile than grain growers, who had homes and villages to defend. Still, they had to protect their cattle, since cattle could walk and were a lot easier to steal. Early Proto-Indo-Europeans must have spent a lot of time stealing each other’s cattle, and retaliating for earlier raids. Lactose tolerance produced healthier and more robust populations, though they had to fight to maintain their high standards.

  Lactose tolerance also developed separately on the Arabian Peninsula, which was dependent on the domestication of camels rather than cattle. And cattle herders in East Africa also acquired it. The increase in food that dairy cattle provided produced a powerful evolutionary draw for a variety of people. This is apparent in a number of African populations including the Maasai.

  LACTOSE TOLERANCE IN AFRICA

  I got to witness this up close when Miriam Ollemoita, a Maasai tribal member and part of the Olduvai Vertebrate Paleontology Project, led me away from the UC Berkeley field station one summer day toward her village in the grassy plains above the Olduvai Gorge in Tanzania. It was late June, the beginning of the dry season, and we passed a middle-aged woman at a shallow well dug into the dry creek bed who was scooping water with a cup and placing each cup into five-gallon buckets
while other females and their giggling children waited in line with their buckets to have the middle-aged woman fill theirs.

  The Maasai are a pastoral people who live principally off milk. They are lactose tolerant, something rather rare among Africans. But they also eat dried meat on special occasions and occasionally mix blood into their milk. It is apparently a healthy diet, since most of the Maasai men at the research station were tall and lean yet agile. Leslea Hlusko, who codirected the project, used Maasai men to help her locate fossils and found them strong and able.

  The village was surrounded by a living wall of twisted branches with sharp thorns and spikes harvested from nearby brush. A woman picked up and moved a bundle of brambles that acted as a gate and allowed us to pass into the village. Inside the wall, we encountered a second wall, which Miriam told me was a safeguard against lions, leopards, and cheetahs, allowing the villagers time to respond if these predators got over the first wall.

  Past the second wall we ran into a group of goats herded by young boys, who gathered around to watch as two of them milked the goats. Miriam told me that much of the herding was divided into three groups, with the younger boys guarding the goats, the teenage boys guarding the sheep, and the grown-up men guarding the cattle.

  The cattle had already been moved from the village to an upland area that had year-round water. Miriam told me the men, including her husband, went with the cattle. She took me through another wall to the center of the village, where a group of boys and several women guarded the newborn goats and sheep. The villagers had erected three walls to protect these animals, since lions, leopards, and cheetahs considered baby goats delicious.

  Back in the 1940s, the Maasai were driven out of many of the wildlife parks, including the Serengeti. Their culture was not always compatible with national park rules, particularly since the 1980s, when tourism in these parks became the leading source of income for Kenyan and Tanzanian governments. But traditionally young Maasai men were supposed to take down a lion to be initiated into the tribe. To do this, villagers ringed the local forest and drove a lion into the path of the Maasai initiate, who had to kill the lion with a spear to prove his manhood. Some Maasai members will tell you this initiation rite is no longer practiced, but others, including Miriam, say it still is.

  The village was a group of dome-shaped huts made of bent branches. A woman knelt on the top of one of the structures, spreading cow dung over the branch frames. I entered one of the huts behind Miriam and was greeted with pitch-darkness. She led me to a small bench beside a small, smoldering fire in the middle of the hut. Smoke from the fire drove out mosquitoes and other insects. As my eyes slowly adjusted to the darkness, I could see that there were little alcoves around the fire where groups of children and adults gathered. Within the alcoves, Maasai beds made with tightly stretched cattle hides were strung wall to wall. The Maasai in the hut were as friendly as they were in the field station, even allowing me to take their picture.

  Though the Maasai are not directly related to Proto-Indo-Europeans, they have arrived in the present with some of the same genetic adaptations that gave Indo-Europeans control over much of the world. The Maasai may not have garnered as much of the world’s material wealth, but lactose tolerance had given them a way of life that has made their tribe the strongest and noblest in the region.

  Scientists believe that Homo sapiens was once pushed to the edge of extinction in East Africa. About seventy-five thousand years ago an eruption occurred on the Indonesian island of Sumatra. The eruption created Lake Toba, the largest crater lake in the world, but it sent three thousand cubic kilometers of rock into the air in a giant plume that spread west over Africa and Asia, enveloping everything in dust, ash, and rock. Giant rafts of pumice filled the Indian Ocean, and some of it even reached Antarctica. Dust blocked out the sun and stopped photosynthesis, which killed the vegetation and therefore the creatures that depended on that vegetation for food. Cheetahs, chimpanzees, tigers, and orangutans were pushed to the edge of extinction along with the native population.

  Because of this, the numbers of Homo sapiens may have shrunk to several thousand, about the size of an urban high school. The evidence for this genetic bottleneck is the vast similarity between this group and modern humans. We are almost indistinguishable from each other genetically. The foreign bacteria in our intestines are more variable than the cells in our own tissues. The Lake Toba eruption is partly to blame for this lack of biodiversity.

  The blast appeared around the same time as man’s great cultural advancement, about the time that we started talking, painting the walls in caves, making jewelry, and conquering the world. The famous evolutionary biologist and author Richard Dawkins suggests in The Ancestor’s Tale: A Pilgrimage to the Dawn of Evolution that the bottleneck created a situation whereby rare genes—Neanderthal DNA or some other mutation—spread through our species. Charles C. Mann, who wrote 1491: New Revelations of the Americas Before Columbus, describes it as the moment when Homo sapiens 1.0 upgraded to Homo sapiens 2.0.

  But a bottleneck limits the diversity of genes to a point whereby the species as a whole is more susceptible to a single calamity, whether by epidemic or a sudden change in climate. Our genetics, in other words, could foreshadow our extinction.

  According to findings published in 2012 in the journal Nature Communications, large-bodied herbivorous dinosaurs were declining during the last twelve million years of the Cretaceous, while midsize herbivores and carnivorous dinosaurs were holding their own. Did sudden volcanic eruptions or an asteroid impact strike down dinosaurs during their prime? Stephen Brusatte, a Chancellor’s Fellow, School of GeoSciences, University of Edinburgh, and lead author of the paper, says, “We found that it was probably much more complex than that, and maybe not the sudden catastrophe that is often portrayed.” The Cretaceous extinction, which killed off the dinosaurs 65 million years ago, may not have been the “terrible weekend” scenario that some scientists like to believe. The dinosaur extinction may have been rooted in a much longer-running process that made the dinosaurs susceptible to the asteroid as well as the volcanic activity that was ongoing at that time in the Deccan Traps in west-central India, one of the largest volcanic features on earth.

  Says Olazul’s science director, Frank Hurd: “Eliminating so many other species of animals, lowering the biodiversity of life in general, may have been convenient for Homo sapiens, but in the end it may lower our own outlook for survival.”

  GLOBAL WARNING

  Climate change has been on meteorologists’ radar for several decades. Years back it was front-page news in the scientific community as well as the popular press. Now if you attend any of the science conventions, there appears to be a sense of resignation: it’s happening, so we’ll have to adapt to it. Man seems reluctant to make the changes necessary to stop it.

  We are currently in an interglacial period where the climate has stayed rather stable. The trouble is we’ve come to expect it. Our present interglacial period is simply the most recent interglacial in a series of glacial cycles that have warmed and cooled the earth now for more than 2.5 million years.

  IPCC predictions based on past evidence entered into computer models (to determine how climate will change in the face of rising greenhouse gases) predict that mean average global temperature will rise from 3.2 to 7.1 degrees Fahrenheit (1.8 to 4 degrees Celsius) by 2100. This is their “best estimate,” from a range of estimates that go as high as 11.5 degrees Fahrenheit (6.4 degree Celsius). These predictions are partly gleaned from cores drilled into the Greenland and Antarctic ice caps as well as into the ocean floor. Some of the ice cores even bring up samples of ancient air to measure. To get a perspective on how grave those predictions are, you must consider that the difference between the current interglacial period and the last ice age is only about 10.1 degrees Fahrenheit (5.6 degrees Celsius).

  Highly resolved ice cores from Greenland and Antarctica reveal twenty abrupt shifts in climate during the last ice age. In other words,
abrupt climate change is part of the climate picture. We’re spoiled right now because things have been so stable, but climate can shift suddenly and dramatically and remain that way for long periods.

  The Younger Dryas event is one of the best-known examples of abrupt climate change. About 14,500 years ago, the earth’s climate began to shift from its cold glacial world into a warmer interglacial one. Partway through this transition, however, temperatures in the northern hemisphere suddenly reversed, returning to near-glacial conditions. The Younger Dryas event is named after the Dryas flower, a cold-adapted plant common in Europe during this time. The end of the Younger Dryas, about 11,500 years ago, was particularly abrupt. In Greenland, temperatures rose 18 degrees Fahrenheit (10 degrees Celsius) in a single decade.

  Man has been around for two hundred thousand years and has gone through two glacial cycles, so we may be more resilient than we’re given credit for. But man has so altered the terrain of planet Earth that there is no longer enough room for nature to adapt. Species that once moved north or uphill to deal with climate change may find roads, parking lots, cities, and megastructures in the way. We’ve put most of our plants and animals into tightly controlled parks, so they can’t leave and migrate north when the weather gets too hot.

  During the last interglacial period, the Eemian, the world was a lot hotter. Ocean surfaces toward the peak of the Eemian rose six to ten feet and stayed that way for several thousand years. Salt water covered much of Northern Europe, turning Sweden and Norway into an island. Salt water also covered the western Siberian plains. The Nile River overflowed, providing a cap to Mediterranean waters that cut off the supply of oxygen to the bottom, producing thick layers of organic ooze recorded today in sediment cores taken off the coast of Egypt. Forests blanketed the Sahara and extended their ranges much farther north than they do today.