Marine Mammal Evolution and Human Adaptation in the Arctic
Environmental pressures at the top of the Earth produce evolutionary impacts

By Henry Huntington

Charles Darwin's "On the Origin of Species" led, among other things, to scientific and public acceptance of the idea that species, including ours, can and do change over time. The mechanisms of change—competition, selection, adaptation—operate today, most visibly in surroundings that also are rapidly changing. Arctic species and societies at the top of the Earth's Northern Hemisphere, for example, are under immense environmental pressures from global climate change that result in both animals and people making observable, behavioral adjustments for survival.  The evolutionary impacts on both are worth noting.

The defining feature of the Arctic marine environment is its sea ice, which is currently threatened by rising regional temperatures. Available evidence suggests the Arctic has had year-round ice for the past 800,000 years, long enough for many species to evolve in and adapt to its presence. Bowhead whales are capable of breaking ice up to two feet thick in order to make breathing holes. Beluga whales navigate through hundreds of miles of pack ice without difficulty. Seals use ice to rest and use the snow that drifts by pressure ridges to make dens for bearing their pups. Polar bears do not hibernate like their brown bear cousins, but roam the ice throughout the winter, hunting seals.

Within the past 40,000 years, humans have moved into the Arctic in increasing numbers, perhaps attracted by opportunity, perhaps given a push from neighbors.  The existing animal population made it possible for them to adapt to the sea ice environment, establish Arctic cultures and even thrive despite the climate, the prolonged winter darkness and the isolation. For many Arctic peoples, these marine resources—marine mammals in particular— have been a primary source of nutritional and cultural sustenance.

But new challenges have arisen in the modern era for hunting cultures, such as the Inuit or Eskimo peoples, who have a long, historical relationship with Arctic animals. Among these, climate change threatens to force some Arctic species away from their usual ranges, out of reach of coastal communities.  As Arctic species migrate away, some subarctic species may move north to fill the gap.  Alternatively, we may also see some Arctic species adapt and evolve.

Early evidence for these changes has already been observed.  In 2007, sea ice retreated far from shallow-water feeding areas in the Chukchi Sea, and walrus hauled out on land in northern Alaska for the first time, an example of potential new behavioral adaptations. In Canada, polar bears have interbred with brown bears, raising the possibility of a new species that could perhaps survive better in the increasingly ice-free Arctic.

Cultural responses of people dependent on these animals will be determined in large part by the environment, but that response will be heavily mediated through social mechanisms such as regulation, culture, perception and technology.  So, while the evolution of new species may occur, the evolution of traditional arctic cultures may also take place.

Arctic societies have adapted to both slow and rapid changes in the past, and will again adapt to changes as they occur. In doing so, those societies will lose some cultural opportunities and gain new ones. Arctic species may adapt, may evolve or may go extinct.

As the prospect of an ice-free Arctic becomes ever more plausible, we should recognize that such a change means losing the true Arctic, leaving us with a subarctic that stretches to the North Pole. What that subarctic will look like remains to be seen—for people, for animals and for ecosystems. This giant, though unintended, experiment will show how some of Darwin's ideas play out, and perhaps it will illuminate the differences between natural selection in the biological world and cultural adaptation among humans.

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Henry Huntington is an independent researcher living in Eagle River, Alaska.  His work examines relationships between people and their environment, primarily in Alaska and other Arctic locations.  He documents traditional knowledge of Arctic peoples, looks at the impacts of climate change in the region and assesses likely impacts to Arctic marine mammals from various threats including climate change and industrialization.  He writes about his research for dozens of scientific journals and for general audiences.  The National Science Foundation supports his research on human responses to changing climate in Alaska and Nepal.

Please see the Resources section for the Bibliography/Additional Reading list for this essay.

Origin and Evolution of Life on a Frozen Earth
Scientists debate whether life's start was hot or cold

By John C. Priscu

The origin of life on Earth is one of the most debated issues in science. Despite ideas put forth by early philosophers, it was Charles Darwin who first posed an explanation for life's origin that complemented his evolutionary theory of life on Earth. In a letter written in 1871 to botanist Joseph Hooker, Darwin envisioned:

"It is often said that all the conditions for the first production of a living organism are present, which could ever have been present. But if (and Oh! what a big if!) we could conceive in some warm little pond, with all sorts of ammonia and phosphoric salts, light, heat, electricity, etc., present, that a protein compound was chemically formed ready to undergo still more complex changes, at the present day such matter would be instantly devoured or absorbed, which would not have been the case before living creatures were formed."

Darwin's "warm little pond" idea was supported experimentally by two University of Chicago researchers in the early 1950s, Stanley Miller and Harold Urey, who showed amino acids, the building blocks for protein, could be formed when electric shocks were introduced to a flask of water containing the gases methane, hydrogen and ammonia. Although efforts to understand the origin of life have been hampered by lack of direct evidence, these early experiments led many to believe that life on Earth had a "hot start." The discovery of hot-loving microorganisms, called thermophiles, supported this concept. Subsequent study of thermophiles led to the conclusion that the last common ancestor evolved in a hot environment and prompted speculation that life originated not in a warm pond, but in a very hot one. This hypothesis is still 'hotly' debated by researchers who believe that such classifications are strongly biased by the use of a single gene for the construction of the tree of life. They argue that deep branching tells us nothing about what came before the common ancestor, and that hot temperatures are not compatible with the stability of structural and functional components of living cells that existed before the advent of life.

Recent discoveries of cold-loving microbes, dubbed psychrophiles, living in solid ice have extended the known boundaries for life on Earth and provided the basis for new theories on the origin and evolution of organisms on our planet. Data obtained over the last 10 years have shown that bacteria inhabit polar ice sheets as well as temperate glaciers. Little information exists on atmospheric and geological conditions during the period when life originated on our planet, some three to four billion years ago. However, we do know that the luminosity of the sun was about 30 percent lower during this period, producing what could have been a subzero world. The half-lives of prebiotic molecules are much longer near the freezing point of water compared to half-lives at the boiling point. Stability in these precursor molecules is essential to the development of the molecular complexity required to initiate life.

Darwin's original ideas of a warm little pond are based to some degree on a habitat that can produce a high concentration of prebiotic molecules. Freezing concentrates molecules, allowing for a high probability of self organization into more complex molecules, while at the same time, reducing the potential to degrade the molecules. The mineral surfaces within ice veins, and inclusions associated with impurities also provide a scaffolding to assist with the synthesis and assembly of complex molecules. Recently, experiments have shown that simple monomeric molecules concentrated in ice veins for almost 30 years can produce precursors for nucleic acid bases.

Though more research is required to determine whether life originated in hot or cold environments—or both independently, it is highly probable that cold environments have acted as a refuge for life during major glaciations. Around 600 million years ago during Earth's Neoproterozoic Era, early microbes endured an ice age with such intensity that even the tropics froze over. According to this "Snowball Earth Hypothesis," the Earth would have been completely ice-covered for 10 million years or more, with ice thickness exceeding one kilometer. Only the hardiest of microbes would have survived this extreme environmental circumstance, and perhaps icy refuges may have served as oases for life during these lengthy crises. The concentration of microbes within ice veins in this frozen environment would favor intense chemical and biological interactions between species, which would entice the development of symbiotic associations, and perhaps influence the development of more complex life-forms through evolutionary time. As such, these ice-bound habitats provided opportunities for microbial evolution, and the acquired biological innovations may have triggered the Cambrian explosion, or the seemingly sudden appearance of most major groups of complex organisms, which occurred immediately after this snowball Earth event.

Clearly, there is growing evidence in favor of a cold origin of life on our planet and future biological research on icy environments will provide more clues to the origin and evolution of life on Earth, as well as other icy worlds. Although the lack of evidence from ancient Earth means we may never know precisely how life began, Darwin's warm little pond hypothesis certainly played a seminal role in molding current notions on the subject.  Darwin appeared cognizant of this fact when he added the following line in his 1871 letter to Joseph Hooker: "It is mere rubbish thinking at present of the origin of life; one might as well think of the origin of matter."

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John C. Priscu is a professor of ecology at Montana State University in Bozeman, Mont. He is a leading expert on polar ecology with 25 years of work in Antarctica where he has studied life associated with the ice sheets as well as sea and lake ice. He investigates ecological processes in these environments that allow organisms to survive and evolve over long temporal and broad spatial scales. The National Science Foundation has supported his research since its inception.

Please see the Resources section for the Bibliography/Additional Reading list for this essay.

Getting Into and Out of Antarctica
Tracking intercontinental animal migration through the ages

By Ross MacPhee

Recently, paleontologists made a remarkable find: a 10-pound, meat-eating frog so fearsome that its discoverers worked a name synonymous with Satan into its scientific label: Beelzebufo, or devil-frog. Some 65 million years ago on the island of Madagascar, nearly 250 miles off the coast of Africa, our lemur-like cousins may have been pursued by Beelzebufo. Scientists are interested in the evolution of the giant devil-frog, but even more intrigued by the fact that Beelzebufo's closest relatives live in faraway South America rather than next door in Africa.

Making sense of such puzzles is part of the science of biogeography, the study of the distribution of organisms in space and time. Biogeography's development is associated with Alfred Wallace, Charles Darwin's contemporary and co-originator of the theory of evolution by natural selection. Wallace knew nothing of plate tectonics—the idea that the Earth's surface is divided into rigid plates that move relative to each other—but he understood that the face of the planet is constantly changing. The existence of supercontinents, single landmasses existing hundreds of millions of years ago that consisted of all the modern continents, is an idea built on principles of plate tectonics. These supercontinents and their associated land bridges may have formed passageways for the distribution of organisms like the devil-frog and its relatives.

Some of the best evidence for this theory comes from the polar regions of Antarctica. Nearly devoid of terrestrial life today, Antarctica appears to have been an important animal crossroads some 45-80 million years ago, the time when mammals rose to dominance as the dinosaurs went extinct. Fossils from islands next to the Antarctic Peninsula include not just dinosaurs, birds and mammals, but also sharks, bony fishes and marine reptiles that together reveal an Antarctica with a subtropical climate. But how did these animals get there? One possibility is that they walked across a land bridge—the Scotia Portal—that connected the Antarctic Peninsula with South America. This land bridge is thought to have been broken about 40 million years ago, when the Drake Passage opened between the southern tip of South America and the South Shetland Islands of Antarctica. After this, Antarctica began heading into its deep freeze.

The Scotia Portal could also account for the presence of other mammal fossils including opossums, sloths and other distinctively South American animals on Antarctic islands. Opossums are marsupials, which today form a major part of regional mammal groupings only in Australia and nearby New Guinea. But what does that distribution imply? We know from tectonic evidence that Australia finally separated from east Antarctica around 64 million years ago. The question is, were ancestral Antarctic marsupials already on board? Almost certainly. Indeed, some groups of marsupials may have actually evolved new forms in Antarctica before traveling onward.

Well to the west, Antarctica was connected to Madagascar, India, Africa and South America until about 110-120 million years ago. When these landmasses then began to move northward, land-bound animal movements to or through Antarctica should have ended; however, analysis of other fossils from the same rocks that yielded the devil-frog indicate that some animal species may have transferred after the continental breakup. This may have been possible by another land connection—the Enderby Portal—that persisted between Madagascar and east Antarctica. There are also two other alternatives, both considered quite unlikely by biogeographers.

The controversies concerning how ancient Antarctica facilitated the distribution of animals like mammals are far from settled, but that is all to the good. Apparent conflicts between biogeographical inferences and plate-tectonic reconstructions should be regarded as places where interesting scientific problems reside, awaiting solution, not as impediments to understanding. Just as Darwin's and Wallace's understanding of evolution and biogeography incited great leaps forward, new evidence from Earth's polar regions are spurring additional breakthroughs.

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Ross MacPhee is former chairman of the Department of Mammalogy at the American Museum of Natural History, where he has been a curator since 1988. Known for his paleomammalogical research on island extinctions, his most recent work focuses on how extinctions occur, particularly those in which humans are thought to have been implicated during the past 100,000 years. His work includes more than 100 published papers in scientific journals and two edited major collections: Primates and their Relatives in Phylogenetic Perspective (1993), and Extinctions in Near Time: Causes, Contexts, and Consequences (1999). The National Science Foundation supports his work with vertebrate paleontology on Livingston Island in Antarctica.

Please see the Resources section for the Bibliography/Additional Reading list for this essay.