The Next Species: The Future of Evolution in the Aftermath of Man (33 page)

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.

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.”

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.

At the height of the warming, hippos pranced and snorted in the Thames River not far from the present city limits of London.
Rhinos ran through the British brush, and water buffalo lowered their horns
to drink from the Rhine.

A return to this type of warming exists in permafrost soils, which underlie much of the Arctic and are large reservoirs of organic carbon—four to five times as much as all the carbon emitted from all fossil fuel combustion and human activities in the last 160 years. The permafrost has already warmed by as much as 4.5 degrees Fahrenheit (2.5 degrees Celsius). If climate change causes the Arctic to get warmer and drier, most of the carbon will be released as CO
₂
. If it gets warmer and wetter, most of the carbon will be released as methane. Neither scenario is cause for optimism.

Take carbon, for example: large carbon releases are already appearing across the interior of Alaska and across the North Slope. And then there is methane: in 2012 scientists measured methane releases over swamps in the Innoko Wilderness in Alaska that were similar to what one might find over a large city.

The Arctic will be one of the first areas to go. The Arctic ice rests on the sea and is only six to nine feet (two to three meters) thick, unlike the ice that covers the continent of Antarctica, which averages 7,086 feet (2,125 meters) in thickness. According to scientists, both the thickness and area of Arctic summer sea ice have declined dramatically over the last thirty years.

Summer may soon be ice-free in the Arctic, but is this a bad thing? An ice-free Arctic, after all, is a valuable potential resource for many countries. Open water in summer and thin ice in winter could be a bonanza for some of the people of Alaska, Canada, Scandinavia, and Russia, though not for wildlife. Curt Stager, author of
Deep Future
, claims an Arctic passage from Europe to the Pacific will save ships the cost of passing through the Panama Canal.
An Arctic passage from Rotterdam to Seattle would be 2,000 nautical miles shorter. And a similar route bypassing the Suez Canal would cut 4,700 nautical miles off the trip from Rotterdam to Yokohama, a boon to international trade.