The Universe Within (23 page)

Raymo’s lead adviser (not the one who called her thesis a c
rock) was thinking about how a new
mountain range would affect global wind currents or serve to make a shadow that could foster storms. Raymo’s insight came from thinking about how a massive mountain range and plateau could affect Earth’s thermostat.

The Tibetan Plateau is a vast barren face of virtually naked rock. It contains over 82 percent of the rock surface area of the planet and reaches over twelve thousand feet high. With the rise of such a plateau came ever growing amounts of rock
erosion on its surface. When we look at the Himalayas, most of us see
a dramatic series of mountains, but Raymo saw a giant vacuum that removes carbon dioxide from the atmosphere—and rivers that flush the carbon into the sea. With decreasing carbon in the atmosphere came a cooler planet. The rise of the Tibetan Plateau led to the shift from a
warm Earth to a cold one; it did so by pulling carbon from the air via
erosion of rock.

Raymo’s theory makes sense of an enormous amount of data, but gaining support for an idea like this is more like winning a criminal case on circumstantial evidence than it is a mathematical proof; only the agreement of a heap of independent lines of evidence can nail the case. Raymo made a very specific prediction: the test lies in using tools that can correlate measurements of the rates of uplift of the plateau—and the levels of weathering of rock—with the amount of carbon in the air. There are altimeters in ancient rocks—
altitude-sensitive plants. Carbon in the air dropped at the time of uplift, but we still do not have the precision to tie the different variables together in the fine detail needed for a test. Whether erosion of the plateau alone is sufficient for the climate change we see or if this acted in concert with other mechanisms remains to be seen.

By 40 million years ago, the map of the world was on the move, and with it the environment that supports life. India slamming into Asia may have heralded an era of dropping levels of carbon dioxide and global cooling, but details of the timing of the
freezing of Antarctica suggest other contributing factors. Forty million years ago, it went from being a rain forest to having a climate much like southern Patagonia today. Then, by about 30 million years ago, the fauna and flora started to diminish, until 20 million years ago, when the first permanent sea ice appeared. The vegetation was largely that of stunted tundra by this time. Ten million years ago desolation was complete.

Look at a map, and you’ll notice that the
Northern Hemisphere
is mostly brown land and the
Southern Hemisphere is mostly blue ocean: the northern half of Earth is composed of large and mostly connected continents, and the southern one, vast oceans. Inside this simple observation lie clues to the freezing of the planet, the vanquishing of life on Antarctica, and the environmental changes behind much of human history.

By the early 1970s, as the reality of
plate tectonics was being widely acknowledged, one huge patch
of ocean floor remained virtually unexplored: the waters of the southern oceans made famous by the great explorers of Antarctica such as
Robert Falcon Scott,
Ernest Shackleton, and Roald Amundsen. Rough
seas separate icebergs and barren rocky islands, so much so that the latitudes from 40 degrees to 70 degrees in which this southern ocean sits are given nicknames: the “roaring 40s, furious 50s, and shrieking 60s.” This was among the last regions of the ocean floor to be sampled for a good reason. The
ocean currents and winds make for a forbidding sea.

Coming off their successes mapping the floors of the
Atlantic and the Pacific, the ocean-mapping teams that supported the work of people like Heezen and Tharp turned to this southern patch. From 1972 to 1976, expeditions were sent to
core about twenty-six sites to look at the sediments of the ocean bottom. At each stop in the ocean, at a site determined by studying maps at home, a winch returned a plug of
seafloor captured from a core at the bottom. Each rock was studied chemically to reveal its age and origins, and the structure of the ocean bottom was mapped just as Marie Tharp and Bruce Heezen had done a decade before in the Atlantic.

The cores from the sea bottom changed the way we look at the southern world. Surrounding Antarctica like a
ring is a huge
rift valley with a molten core. This, like the rift at the bottom of the Atlantic, is a place where new seafloor is being made, where the plate is actually
spreading. The jigsaw puzzle of the South, contained in the shape of the continents and
Colbert’s
Lystrosaurus
discovery, became clear. At one time in the past, the entire
southern part of the globe was indeed one giant super landmass composed of what are today all the southern
continents: Antarctica,
Australia,
South America, and
Africa. The distinctive blue oceans that define our South today weren’t there.

Then, with the birth of this volcanic ring surrounding Antarctica, the continents separated and moved away from their southern neighbor. Three things happened at once: Africa, Australia, and South America moved north, Antarctica became isolated at the
South Pole, and vast seas opened up separating all the southern continents. None of these changes boded well for life near the South Pole.

Just as isolation is bad for people, so too is it for polar continents. The
ocean current that has so vexed mariners for years runs as a ring around Antarctica from east to west. It was born as space was created for it by continents cleaving from Antarctica. Oceans are wonderful ways to transport heat. As an example,
Britain lies at the same latitude as northern
Labrador. One place is relatively mild, the other quite fiercely cold. The reason? Warm currents coming up from the equator keep Britain’s climate mild, whereas the western
Atlantic has no such current. Before Antarctica became isolated,
ocean currents running from the equator brought heat to the continent. When Antarctica separated from the other southern continents, this conveyor of heat stopped, only to be replaced by the
ring current. This change spelled cold for Antarctica: whatever heat existed at the South Pole just escaped into the air, never to be replenished by warm waters. Life on Antarctica literally froze to death or skedaddled to greener pastures elsewhere.

The emerging map of the world changed climate and life. Moving continents and expanding seafloor brought new patterns of ocean circulation,
erosion, and levels of
carbon dioxide in the atmosphere, thereby dooming an entire continent. The consequences extend as far as the eye can see.

Humans are visual animals built to detect patterns in a messy world. Bush pilots’ eyes, like those of
Paul Tudge, are trained to spot objects on a flight. Children can find hidden objects in puzzles or pictures, fly
fishermen learn the water by seeing shadows below the ripples in streams, and radiologists save lives by deciphering shadows on images: our species has survived by finding patterns hidden in the apparent chaos around us. This ability lies in the interplay between our eyes and our
brains: together they help us learn to see, survive, and thrive.

We live in a world so awash in vivid hues that it is easy to forget we perceive only a tiny fraction of the
colors in front of our eyes. Light arrives to us in a wide spectrum of
wavelengths, from
ultraviolet to
infrared. Gadgets such as night-vision goggles provide only a glimmer of these hidden frequencies. Other creatures can see a broader range of
colors naturally. Birds perceive many more shades of blue, as do some species of fish. Each species—whether eagle, trout, or human—is tuned to experience and perceive its world in a particular way. And our
perception has its roots in the forces that froze the poles of Earth.

Human eyes, like those of other mammals, have a postage-stamp-sized retina in the back that receives light from the lens. Plastered on the retina are about 5 million specialized cells that are like little receivers to detect red, yellow, and blue—the three primary colors of light. This ability is conferred on each cell by a specialized
protein inside that undergoes a distinctive change in shape when the right color hits it. The cells in the retina can discriminate about a hundred different shades of light. When these signals hit the brain, they are combined, allowing us to perceive a palette of about 2.3 million different colors.

Our closest
primate cousins of the Old World—
monkeys, gorillas, chimps, and orangutans—can see the same palette of
colors as we do. We share a very similar makeup, which extends to the proteins inside the retina we use to perceive color. More distantly related
primates, such as those that live in South America, do not see in color exclusively: in some species the males are color-blind. Ever since the nineteenth century, primatologists have known about a big split in our primate family tree: all Old World monkeys have full
color vision, whereas this trait is lacking in their New World cousins. Is there also a difference in lifestyle that explains the ability to see in vivid color?

The first hint came from a surprising finding.
Howler monkeys, as the name implies, have a distinctive cry. They were described by the great explorer
Alexander von Humboldt in the nineteenth century as having “eyes, voice, and gait indicative of melancholy.” Scientists studying their behaviors and visual structures in the 1990s discovered that unlike South American monkeys, all howlers are able to see in the same spectrum of color as we do. There is a huge difference in the diets of howlers and their South American cousins. All other monkeys eat mostly fruit, whereas howlers exist on leaves.

This observation motivated a young graduate student,
Nathaniel Dominy, a former football player at the
Johns Hopkins University, to think in a new way about how color vision arose. Perhaps the lessons of the howlers is general, he thought, and there is a major difference in diet that explains why our branch of the primate family tree sees in color.

Kibale National Park in western Uganda sits among a rich forest landscape of evergreen and mixed deciduous trees. Leopards, hornbills, and distinctive forest elephants—unusually hairy and small—dwell there. So too does an astounding di-versity of primates. A whopping thirteen species—including chimpanzees—make the park their home.

Kibale is also home to a fourteenth species of primate—humans—many of whom live in the
Makerere University Biological
Field Station to study their primate cousins. In 1999, Dominy traveled there with the simple goal of watching the monkeys eat.

Dominy and his research adviser,
Peter Lucas, had a plan: they were going to look at each type of primate in the reserve and quantify exactly what it ate and when. If there was a pattern to the diets, they were going to find it. The crew wasn’t just armed with notepads; they carried a backpack laboratory that was described in a later scientific paper with a title that says it all:
“Field Kit to Characterize Physical, Chemical, and Spatial Aspects of Potential Primate Foods.” Inside the backpack was a materials testing device designed to measure toughness of foods; a spectrometer to quantify color and basic nutritional properties of foods; and a number of other gizmos to record the shape and weight of whatever the monkeys gobbled up.

Dominy, Lucas, and their team spent ten months watching primates. When they weren’t interrupted by the threat of bandits or terrorists (at one point they were forced to retreat to the American embassy in Uganda), they worked around the clock, eventually logging 1,170 hours of observations. They would watch the animal as it consumed its meal, then hit the leftovers with their backpack lab. In the end, they found that the monkeys consumed about 118 different kinds of plants.

Back home, as they crunched the data, a pattern emerged. Species with color vision preferentially selected leaves that varied on the red-green color scale. That is, they were differentiating foods that animals lacking color vision could never even perceive. And what of the foods that they selected using their color vision? These morsels uniformly had the highest amount of
protein for the least amount of toughness. The primates’ mothers must have been pleased: they ate things that were both good for them and easy to digest. And the biggest cue, red color, was something that only species with full color vision could detect.

To Dominy and his colleagues, a hypothesis emerged: color
vision enabled creatures to discriminate among different kinds of leaves and locate the most nutritious ones. This advantage gained new prominence when climates changed and plants responded.

More clues to
color vision are nestled inside DNA. Mammals that lack color vision have only two
proteins to perceive color; we and the Old World apes that perceive colors have three. In 1999, as DNA technology became cheaper and more powerful, the actual composition of these proteins could be compared, giving a detailed look at their chemical structure. Hidden inside the sequences was a major clue to the origin
of color vision. The three proteins that allow us to see colors are duplicates of the two seen in other mammals. By comparing the sequences in the new copies with the old ones, we can get an estimate of when the duplication happened. All creatures with the three genes trace their lineage back to about 40 to 30 million years ago, the likely time when color vision arose in our closest ape ancestors.