Chapter Content
**Chapter 41: The Deep Chill**
*“I had a dream, which was not all a dream.
The bright sun was extinguished, and the stars
Did wander darkling in the eternal space...”*
—Lord Byron, *Darkness*
The year was 1815. On the island of Sumbawa, nestled in the Indonesian archipelago, a volcano named Tambora, previously dormant, erupted with catastrophic force. The sheer volume of molten rock spewed forth, coupled with the devastating tsunamis that followed, claimed the lives of an estimated one hundred thousand souls. No living person had ever witnessed such raw power. Tambora dwarfed any eruption in recent memory, being the most significant volcanic event in nearly ten thousand years – a staggering fifteen times the magnitude of the 1980 eruption of Mount St. Helens in the United States, releasing energy equivalent to sixty thousand Hiroshima-sized atomic bombs.
News traveled at a snail’s pace back then. It took seven long months for a brief report, essentially a merchant’s correspondence, to surface in London's *The Times*. But the effects of the cataclysm were already being felt across the globe. Two hundred forty cubic kilometers of ash and dust choked the atmosphere, dimming the sunlight and causing a drop in global temperatures. The sunsets became eerily subdued, a phenomenon eagerly captured by the English painter J.M.W. Turner. However, for most, life became a struggle in a perpetual, oppressive twilight, a gloom that inspired Byron to pen the verses that begin this chapter.
Spring faltered, summer offered no warmth, and 1816 became known as "The Year Without a Summer.” Crop failures were widespread. In Ireland, famine and a typhus epidemic claimed sixty-five thousand lives. Across the Atlantic in New England, the year was dubbed "Eighteen Hundred and Froze to Death.” Frosts persisted into June, preventing seeds from germinating. Livestock perished from lack of feed or were slaughtered prematurely. By any measure, 1816 was a disastrous year – arguably the worst crisis faced by modern farmers. Yet, the global temperature dipped by less than a single degree Celsius. This event served as a stark lesson, highlighting the surprising vulnerability of Earth’s climate regulation system.
The 19th century was, in truth, not a particularly cold period. For the two centuries prior, Europe and North America had experienced what we now call a mini ice age. This period facilitated activities like the annual frost fairs held on the frozen River Thames or skating races along Dutch canals – sights now almost unthinkable. In short, it was an era where people were accustomed to the cold. This context helps explain why 19th-century geologists were slow to recognize they were living in a comparatively mild interlude, surrounded by landscapes sculpted by the immense power of past glaciers and cold snaps that would have easily put any frost fair out of business.
They were aware that something extraordinary had occurred in the past. Across the European continent, perplexing anomalies abounded – the skeletal remains of arctic reindeer discovered in the balmy south of France, massive boulders perched incongruously atop landscapes where they didn't belong. This often led to seemingly bold, yet ultimately flawed, interpretations. A French naturalist named De Luc attempted to explain the presence of enormous granite rocks on higher limestone levels in the Jura Mountains by suggesting compressed air within caverns had launched them there, like a cork from a popgun. While this explanation failed to account for the rocks' long-distance journeys, 19th-century thinkers often prioritized internal consistency over aligning their theories with the tangible evidence of rock movements.
Arthur Hallam, a significant British geologist, suggested that James Hutton, the father of 18th-century geology, would have immediately understood the significance of the fractured valleys, the polished striations, the rock-strewn moraines, and other clues that littered the Swiss landscape had he visited the country himself. All pointed to the passage of ice sheets. Sadly, Hutton was no traveler. However, even with secondhand information, he boldly rejected the idea that massive stones were washed up onto mountain slopes over 1000 meters high, correctly pointing out that no flood could have ever carried rocks, becoming one of the first proponents of large-scale glacial action. Unfortunately, his views did not gain wide acceptance; for nearly half a century, most naturalists maintained that the marks on rocks were simply the results of passing carts or even hobnail boots.
Conversely, local farmers, unburdened by scientific orthodoxy, possessed greater insight. The Swiss naturalist Jean de Charpentier recounted a story: In 1834, while walking with a Swiss woodcutter along a country lane, they casually discussed the ubiquitous boulders. The woodcutter matter-of-factly stated that the rocks originated from the Grimsel region far away. "When I asked how these rocks came to his region," Charpentier wrote, "he unhesitatingly replied: 'The Grimsel glacier brought them here along the valley, for it once extended as far as the town of Berne.'"
Charpentier was delighted because he had reached the same conclusion independently. However, when he presented his ideas at scientific gatherings, he faced ridicule. Charpentier’s close friend, Swiss naturalist Louis Agassiz, initially greeted the ideas with skepticism, then gradual acceptance, and ultimately, full-throated support.
Agassiz, who had studied with Cuvier in Paris, held a professorship in natural history at the Academy of Neuchâtel in Switzerland. A friend named Karl Schimper was a botanist. It was Schimper, in 1837, who actually coined the term Ice Age (Eizeit in German). He proposed that widespread evidence suggested that not only had thick ice covered the Swiss Alps, but vast regions of Europe, Asia, and North America as well. This was an incredibly radical notion. He lent his notes to Agassiz – a decision he would later regret, as Agassiz increasingly appropriated his ideas, and Schimper rightfully felt he was being robbed of credit for his theory. Charpentier, too, would eventually become estranged from his old friend. Alexander von Humboldt, another friend of Agassiz, once described the three stages of scientific discovery: First, people deny that it is true; then they deny that it is important; finally, they credit the wrong person. Humboldt had Agassiz in mind, at least partly, when he stated this.
Regardless, Agassiz dedicated himself to the cause. He traversed every terrain he could to understand the powers of glaciation -- delving into perilous crevasses, scaling treacherous Alpine peaks, often unknowingly being the first human to summit these landmarks. Everywhere he went, Agassiz's theory was met with disbelief. Humboldt urged him to cease his "glacial mania" and return to the study of fossil fish, in which he was an expert, but Agassiz was a man possessed by an idea.
In Britain, support for Agassiz’s theory was even scarcer, as most naturalists had never seen a glacier and struggled to grasp its colossal force. "Shall we ascribe all the scraping and polishing of rock surfaces solely to the action of glaciers?" Roderick Murchison sarcastically inquired at a meeting, clearly envisioning those surfaces coated only with a thin sheet of frost. He remained deeply skeptical of those "glacial maniac" geologists until his death. William Hopkins, professor at Cambridge and a leading figure in the Geological Society, echoed these sentiments, declaring the idea that glaciers could move rocks was "mechanically absurd" and hardly worthy of the Society’s attention.
Undeterred, Agassiz tirelessly traveled and lectured, proselytizing his theory. In 1840, he presented a paper at the British Association for the Advancement of Science meeting in Glasgow, only to be publicly criticized by the eminent Charles Lyell. The following year, the Geological Society of Edinburgh passed a resolution acknowledging that Agassiz's theory might have some merit but was certainly inapplicable to Scotland.
Lyell eventually changed his mind. His epiphany came when he suddenly realized that a pile of moraine stones near his Scottish home – a long ridge of rocks he had passed hundreds of times – could only have been deposited there by a glacier. But even with his inner transformation, Lyell lacked the courage to publicly endorse the Ice Age theory. It was a particularly difficult time for Agassiz. His marriage was falling apart, Schimper accused him of plagiarism, Charpentier wouldn't speak to him, and Lyell, the greatest geologist of his time, was only giving lukewarm and wavering approval.
In 1846, Agassiz embarked on a lecture tour in the United States, where he found the recognition he craved. Harvard University hired him as a professor and established a world-class Museum of Comparative Zoology for him. Settling in New England, which likely helped because the long, frigid winters generated some sympathy for theories about extended cold periods. Six years later, Agassiz made his first scientific expedition to Greenland, which further helped because they found that the whole island was covered in ice like he said the world used to be. His theory finally began to gain real traction. Agassiz's theory had a fatal flaw: He could not explain what caused the Ice Age. Help would come from an unexpected place.
In the 1860s, British newspapers and academic journals began to receive articles on hydrostatics, electricity, and other subjects from a James Croll of Anderson’s University in Glasgow. One article theorized that changes in Earth's orbit might be the cause of glacial periods. Published in the *Philosophical Magazine* in 1864, the paper was immediately recognized as being of the highest academic quality. But surprise and perhaps a touch of embarrassment washed over the scientific community when it was discovered that Croll was not a faculty member but simply the university's janitor.
Born into poverty in 1821, Croll's formal education ended at age thirteen. He held various jobs – carpenter, insurance salesman, temperance hotel keeper – before landing the position of caretaker at Anderson's University (now Strathclyde University) in Glasgow. He convinced his brother to help with his work, and during the quiet evenings, he would steal away to the university library, educating himself in physics, mathematics, astronomy, hydrostatics, and other burgeoning sciences. Gradually, he began writing papers, focusing particularly on Earth's movements and their influence on climate.
Croll was the first to propose that the periodic variations in Earth’s orbit, from elliptical (egg-shaped) to near-circular and back again, could trigger the onset and retreat of glacial periods. Before him, no one had attempted to explain changes in Earth's weather from an astronomical perspective. Thanks to Croll’s compelling theory, the notion that parts of the Earth had once been covered in ice became more widely accepted in Britain. Croll’s genius was finally recognized. He secured a position with the Scottish Geological Survey and received numerous accolades: fellowships from the Royal Society of London and the Scientific Society of New York, an honorary degree from the University of St Andrews, and more.
Sadly, just as Agassiz’s theory finally gained traction in Europe, he was traipsing around unexplored regions of the Americas. Everywhere he looked, including near the equator, he found evidence of glaciation. Eventually, he became convinced that ice had once covered the entire globe, wiping out all the life that God had previously created. None of Agassiz's data supported this idea. Nevertheless, in his adopted America, his standing grew until he became a figure just short of sainthood, so much so that upon his death in 1873, Harvard University deemed it necessary to hire three professors to fill the void he left behind.
However, Agassiz's theories soon became unpopular again. That sometimes happens. Less than a decade after his passing, the new chair of the geology department at Harvard wrote: "The so-called Ice Age… which a few years ago was so popular with glacial geologists is now unhesitatingly abandoned."
The problem, in part, was that Croll's calculations suggested the last glacial period occurred 80,000 years ago, but geological evidence increasingly indicated some kind of serious disruption occurred much more recently, less than 30,000 years ago. Without a plausible explanation for what caused an ice age, the whole theory was on shaky ground. This issue would persist for some time were it not for the arrival of a Serbian scholar named Milutin Milankovitch. Milankovitch had no background in celestial mechanics – he was a trained mechanical engineer – but he became suddenly fascinated by the problem in the early 20th century. He realized that the problem with Croll’s theory was not that it was wrong but that it was too simple.
As the Earth moved through space, it changed not only in the length and shape of its orbit but also in its angle of orientation toward the sun. Its tilt, its wobble, and its eccentricity all changed periodically, all affecting the length and intensity of sunlight striking any point on the planet. In particular, he knew that there were three positional changes that the Earth went through over immense periods of time, these are the obliquity, precession, and eccentricity. Milankovitch suspected that these complex, cyclical variations might somehow be related to the onset and retreat of glacial periods. The difficulty was that the time scales of these changes varied greatly – some roughly every twenty thousand years, others every forty thousand years, and still others every one hundred thousand years, with each cycle off by thousands of years, making it nearly impossible to determine how they intersected over long periods of time. Crucially, Milankovitch needed to calculate how the angle and duration of sunlight striking every latitude on Earth varied with each season over a million years as the three elements varied.
Happily, a task this complex and tedious was perfectly suited to Milankovitch’s temperament. For the next twenty years, even on vacation, Milankovitch incessantly calculated his cycles with pencil and slide rule – a task that can now be done on a computer in a day or two. The work was performed in stolen moments, but in 1914, Milankovitch suddenly had lots of stolen moments. World War I erupted, and he was arrested as a reservist in the Serbian army. For much of the next four years, he was confined to house arrest in Budapest, with lax oversight, requiring only a weekly check-in with police. The rest of the time, he diligently worked in the library of the Hungarian Academy of Sciences. He was perhaps the happiest prisoner of war in history.
The culmination of his labors was published in 1930 in his book *Mathematical Climatology and the Astronomical Theory of Climate Change.* Milankovitch was right, Ice Ages were connected to the Earth's movements. Although like most others, he thought that long cold periods arose from gradually escalating very cold winters. It was the Russian-born German meteorologist Wladimir Köppen -- father-in-law of structural geologist Alfred Wegener -- who realized that the process was more complicated, and more alarming than that.
Köppen realized that ice ages were produced by cool summers, not severe winters. If an area has particularly cool summers, sunlight reflected from the surface intensifies the cold, prompting greater snowfall that often creates permanent ice. As the snow became ice sheets, the area becomes even colder, leading to yet more ice. In the words of glaciologist Gwen Schultz, "The making of an ice sheet does not depend on how much snow falls but how much snow does not melt -- no matter how little." An ice age began, it was supposed, with an unusually mild summer that left snow that did not melt and intensified the cold, "a self-enhancing process," McPhee writes, "and once an ice sheet existed, it began to move." Now you had a moving glacier, and thus an ice age.
In the 1950s, dating techniques were still so crude that no one could correlate what scientists knew about ice ages with Milankovitch's exact cycles, so Milankovitch and his calculations became increasingly unpopular. When he died in 1958, he had still not managed to prove the correctness of his cycles. By this point, in the words of one history of the period, "you would have to look hard to find a geologist or meteorologist who thought that [the calculations] were anything more than antique." It was not until the 1970s, with the improvement in potassium-argon dating techniques for ancient seafloor sediments, that Milankovitch's theory was finally vindicated.
The Milankovitch cycles alone, are not enough to explain Ice Age cycles. Many other factors have to be factored in -- notably, the layout of continents, especially the presence of landmasses at the poles -- but we don’t have a full understanding of it all. However, one view remains that if you moved North America, Eurasia and Greenland 500 km farther north, then we would very likely be in an Ice Age permanently. We seem to have gotten extraordinarily lucky with all the nice weather. We are particularly vague about the cycles for a period of relatively warm climate within an Ice Age called an interglacial. Perhaps frustratingly, the entire history of human civilization -- the development of agriculture, the building of cities, the nurturing of mathematics, literature, science, and everything else -- has occurred within an unusually benign period of weather. Previous interglacials have typically lasted about 8,000 years, we are already 10,000 years in.
The truth is we are still in an ice age, just a diminished one -- though not as diminished as many suppose. At the peak of the last Ice Age, about 20,000 years ago, about 30% of the Earth's land surface was buried in ice. Even now, 10% of the land is under ice. (A further 14% is permanently frozen as permafrost.) Three-quarters of the world's fresh water is locked in ice, and ice sheets are present at both poles -- a situation without equal for most of the Earth's history. The fact that snow falls in winter in many parts of the world and that temperate places such as New Zealand have permanent icecaps seems normal to us but is profoundly unusual in Earth's longer history.
Until fairly recently, for most of its history, the Earth has been mostly warm and has had no permanent ice anywhere. The current ice age -- which in fact is an ice age epoch -- began about 40 million years ago. We are now in a period of extreme mildness. New glaciations always erase the records of previous glaciations, and the farther back you go, the more fragmented the picture before you. But for the past 2.5 million years or so, we appear to have gone through at least 17 significant glaciations -- the period in which *Homo erectus* and then *Homo sapiens* lived. It is often said that the two suspects for the current ice age are the rising of the Himalayas and the formation of the Isthmus of Panama. The former disrupted air currents, the latter disorganized the ocean currents. Over the last 45 million years, the subcontinent of India went on a 2,000-kilometer drift and smashed into the Asian continent. The result was not only that the Himalayas rose but a vast plateau formed behind it. It is believed that increased altitude not only made the climate colder but redirected winds to the north, over North America, making the continent more liable to long periods of severe cold. Then, starting about 5 million years ago, the region of Panama rose out of the sea and connected the continents of North and South America. This affected the flow of warm currents from the Pacific to the Atlantic, and altered the amount of rain that fell over at least half the world. One consequence of this was that Africa became drier, which pushed apes to leave the trees and find new ways of surviving on the emerging savannahs.
In any case, with oceans and continents now in their current locations, we seem to be committed to a long epoch of ice ages. By John McPhee's reckoning, we still have roughly 50 more ice ages to come, each lasting about 100,000 years, before we can look forward to a long period of thawing.
Over the grand sweep of time, for 50 million years, Earth had no regular ice ages, and when they have occurred, they have been of the most amazing scale and duration. The first extensive glaciation occurred about 2.2 billion years ago, followed by 1 billion years or so of relative warmth. The next glaciation was even bigger -- so big, in fact, that some scientists now refer to the period as the Cryogenian or a Super Ice Age. More often, it is called Snowball Earth.
However, "Snowball" hardly conveys just how severe conditions may have been at that time. The theory states that because of a reduction in the amount of solar radiation of about 6% and a reduced ability to generate (or retain) greenhouse gases, the planet failed to retain heat. The planet became a frozen snowball, like present-day Antarctica, with temperatures 45 degrees Celsius lower. The whole planet became solidly frozen over, with oceans as much as 800 meters thick in high latitudes and perhaps dozens of meters thick even in the tropics.
A great problem exists: geologically, it seems that the entire planet was covered in ice, including the equator, yet biologically there seems to be no doubt that some unfrozen water must have been present. First, cyanobacteria survived and photosynthesized. Photosynthesis requires sunlight, but if you look through ice, light is dimmed increasingly quickly, and just a few meters down no light is present. Two explanations are possible: either a very few pockets of unfrozen water did exist (perhaps in localized hotspots) or some form of translucent ice existed -- the latter of which does exist in nature.
If the planet did freeze over, how did it thaw again? The answer is hard to come by. A planet in a frozen state will stay that way forever due to the amount of heat that it reflects. The agency of salvation, it seems, came from within the planet. We may again have to thank the construction of the crust. Volcanoes, we believe, saved us. Eruptions broke through the icy seal, and the resulting heat and gases melted the icy surface and allowed the atmosphere to alter again. Interestingly, this extremely cold period marked the end of the Cambrian Explosion -- the Spring of Life -- though such a Spring was not always sunny, as as the world warmed, it experienced the most violent weather of any era, with immense hurricanes throwing waves as tall as skyscrapers, accompanied by inconceivable rainstorms.
Undoubtedly, tubeworms, clams and other life forms clinging to deep sea vents continued on as if nothing had happened. But nearly all other life on Earth probably came close to extinction. It is an era so remote, and our knowledge of it remains extraordinarily meager.
Compared to the Cryogenian Era, recent ice ages seem small, but they are still enormous by any standards we know today on Earth. The Wisconsin ice sheet that covered Europe and North America was up to 3 kilometers thick in places and was advancing at a rate of 120 meters a year. Even at its outer edges, the ice sheet was nearly 800 meters thick. What a thing to behold! Imagine yourself standing at the base of a wall of ice that tall, behind which stretched millions of square kilometers of a landscape that was all ice save for the odd jagged peak sticking through the ice. Whole landmasses were depressed under the colossal weight of the ice, and even 12,000 years after their retreat, the land still has not fully rebounded. As the slow-moving ice sheets moved, it moved immense boulders and moraines and dropped whole landmasses -- such as Long Island, Cape Cod, Nantucket. It is perhaps no wonder that pre-Agassiz geologists struggled to understand the great landscape-changing power of the ice sheets.
We have no weapons to deflect them if the ice sheets returned. In 1964, in Prince William Sound, Alaska, the largest ice field in North America had the biggest earthquake ever recorded on the continent, 9.2 on the Richter scale. At the fault rupture, the ground rose 6 meters. The earthquake was so powerful that it splashed water from ponds in Texas. But how did this unprecedented seismic event affect the glaciers of Prince William Sound? Not at all. The glaciers shrugged it off and kept advancing.
For a long time, it was thought that the Earth eases in and out of ice ages on cycles lasting hundreds of thousands of years. But we know now that is not the case. Measurements of Greenland's ice cores have provided us with a detailed record of the Earth's climatic changes over the last 100,000 years. What they tell us is not heartening. The record shows that rather than being a stable home, as had once been thought, over recent geological time, the Earth's climate has flickered dizzily between warm and cold.
About 12,000 years ago, near the end of the last major glaciation, the climate warmed, and warmed rapidly. But then, just as abruptly, it snapped back into a thousand-year or so of intense cold. This period is known in scientific literature as the Younger Dryas. (The name derives from a hardy Arctic plant called Dryas, one of the first to reappear in landscapes after ice retreated. There is also an older, less-pronounced event called the Older Dryas.) Toward the end of that millennial freeze, average temperatures again rose suddenly, in some cases as much as 4 degrees Celsius in just two decades. That may not sound like much, but it is enough to transform the climate of Scandinavia into that of the Mediterranean within only 20 years. In localized areas, the changes were even more startling. Ice cores in Greenland show a shift of as much as 8 degrees Celsius within a decade. The change shifted weather patterns and altered biomes. Disturbing in the sparsely populated past, the effect in the present is almost unimaginable.
Most disturbingly, we don’t know -- really know -- what natural phenomena have caused Earth's temperature to change so rapidly. As Elizabeth Kolbert wrote in *The New Yorker*: "No known external force -- and even no hypothesized external force -- corresponds to the swings recorded in the ice cores. There seems to be," she continued, "a system, vast and terrifying, of feedback loops." It likely has to do with disruptions to the normal circulation of oceans and ocean currents, but we are far from understanding it all.
One theory holds that at the start of the Younger Dryas, large volumes of meltwater flowing into the ocean lowered the salinity (and therefore the density) of seawater in the Northern Hemisphere, causing the Gulf Stream to veer south like a driver swerving to avoid a collision. Deprived of the Gulf Stream's warmth, higher latitudes in the Northern Hemisphere reverted to frigid conditions. But this doesn't explain why when the planet warmed again after a thousand years, the Gulf Stream did not return to its former path. Instead, we entered an exceptionally stable period known as the Holocene, which is the period we now live in.
There is no reason to suppose that this period of stability will persist for long. Indeed, some meteorological authorities think our climate is getting worse, and at a faster rate than it did before. It is natural to suppose that global warming would inhibit a return to glacial conditions. Yet, as Kolbert has observed, the last thing you want to do when confronted by unpredictable climatic swings “is start messing around with the system on a planetary scale.” Some even believe rising temperatures might actually hasten the onset of a glacial period. This appears paradoxical, but it is quite logical. A small rise in temperatures will encourage evaporation, which in turn thickens cloud cover. This in turn would permit sustained increases in snow cover at higher latitudes. In effect, global warming may make certain areas of North America and Northern Europe colder. It makes sense, though it is counter-intuitive.
Climate is the product of so many variables – rises and falls in carbon dioxide levels, continental drift, solar activity, alterations in the Milankovitch cycles -- that understanding the past is as difficult as predicting the future. Many things we simply do not understand. For example, for at least 20 million years after Antarctica moved to the South Pole, it was free of ice and covered in vegetation. This today sounds close to impossible.
Even more inexplicable are some of the known habitats of late dinosaurs. British geologist Stephen Trullinger has discovered that the forests within 10 degrees latitude of the Arctic circle were home to large animals, including Tyrannosaurus Rex. "This is utterly perplexing," he wrote, "because at such high latitudes there are three months of total darkness a year." Moreover, evidence now indicates that winters were very cold at these higher latitudes. Oxygen isotope studies show that the late Cretaceous climate of Fairbanks, Alaska, was much the same as it is today. So what was T-Rex doing there? It either seasonally migrated long distances, or it spent long periods of the year in darkness, ice, and snow. In Australia -- which at that point was closer to the South Pole than it is today -- there was no way to move to a milder climate. How did dinosaurs manage to live in these conditions? We can only guess.
One thing to bear in mind, if ice sheets do start to form again, for whatever reason, is that this time, there is a lot more water to work with. The Great Lakes, Hudson Bay, and the thousands of lakes of Canada did not exist and therefore didn't provide materials for the last Ice Age; they are products of it.
On the other hand, the next phase of our history is set to see a great deal more melting than freezing. If all the ice sheets melted, sea levels would rise 60 meters -- twenty stories high -- and virtually every coastal city in the world would be submerged. More likely, at least in the short term, is the collapse of the West Antarctic ice sheet. In the last 50 years, temperatures around Antarctica have increased by 2.5 degrees Celsius, and ice shelf disintegration has greatly accelerated. The geological structure of the region makes large-scale collapse all the more likely. Should this happen, global sea levels would rise – quickly – by an average of between 4.5 and 6 meters.
One thing is apparent: we don't know whether the future holds a frigid climate or a scorching one. The one certainty is that we live on a knife edge.
Incidentally, over the long run, ice ages are not necessarily a bad thing for a planet. Glaciers grind up rocks, leaving behind fresh, fertile soils; they gouge out freshwater lakes, providing rich habitats for hundreds of species; they promote migrations of plants and animals, invigorating the planet. As Tim Flannery put it: "To determine the fate of humanity on a continent, you need only ask the continent one question: 'Have you had a decent ice age?'" With this in mind, we should see how one species of ape has adapted to such changes.