In a laboratory in Japan, a scientist examines an ancient block of ice. It is hard to distinguish at first glance, but the scientist can make out a long, curved tusk encased within it. Inside this mass of ice is the frozen carcass of a baby woolly mammoth that was discovered in the tundra of Siberia. With great care the scientist slowly removes ice from the body, hoping to find intact DNA.
The woolly mammoth is an extinct relative of the elephant. Even though a common ancestor lived many, many thousands of years ago, the elephant is not a direct descendant of the mammoth. In fact, the species diverged into separate evolutionary branches as long as six million years ago. The woolly mammoth first appeared only two million years ago, during the Pleistocene epoch. They survived until as recently as ten thousand years ago, when the last ice age ended. You could say that elephants are evolutionary cousins of the woolly mammoth.
The most obvious difference between these distant cousins is, of course, hair. Shaggy fur, which could grow up to fifty centimeters long, kept the woolly mammoth warm. Elephants have hair as well, but it is short and not thick enough to cover their hides. The prehistoric woolly mammoth grew larger than today's elephants. While archaeological evidence shows that mammoths grew up to four and a half meters high, the largest African elephants can only reach four meters.
Like their elephant cousins, woolly mammoths had tusks. When two elephants in a herd challenge each other, they meet head to head and lock tusks. Mammoths probably wrestled in the same way. But the woolly mammoths' tusks were thicker than elephant tusks, and almost twice as long; some reached five meters in length. Another difference is that mammoth tusks grew in long, sweeping arcs that could reach the ground when the mammoth lowered its head.
Mammoths probably lived in herds, as their elephant cousins do today. But the mammoth lived during an ice age. How did such a large animal survive in such an inhospitable environment? Woolly mammoths had more than a thick coat to protect them from the harsh weather. Underneath their hides woolly mammoths had a layer of fat as thick as eight centimeters, which insulated them from the cold. The woolly mammoth's cold environment also explains why elephants and mammoths have such different ears. African and Indian elephants have large ears, sometimes two square meters in size. During the hot summer, an African elephant fans its ears, sending a cool breeze over its body. Ears are full of tiny blood vessels close to the skin's surface, and waving its large, thin ears also helps an elephant release heat from its body. Of course, mammoths had to face cold weather, not hot. Their ears evolved into a much smaller size so that their bodies would retain heat and not lose it to the cold air.
Woolly mammoths were herbivores, and finding food in the snow-covered plains of the last ice age was quite difficult. But even today large herbivores, like the reindeer and the yak, live in great numbers in northern climates. Vegetation can be found under the snow. Many scientists believe that mammoths made good use of their tusks, swinging them from side to side to clear away snow and expose the plants underneath. The mammoth's long, curved tusks seem suited to this purpose. Many types of nutritious plant life that are extinct today grew during the last ice age, so the woolly mammoth would have had enough to feed on. Also mammoth herds likely traveled across the vast North to find the best feeding areas, as reindeer do today.
The woolly mammoth's environment was very different from the one we know today. During the Pleistocene, giant sloths as tall as elephants, relatives of today's slow-moving tree sloths, walked the earth. The strange glyptodon, with its turtle-like shell, was as big as a car. Saber-toothed tigers and giant bears were dangerous predators. As the last ice age came to an end, most of these large animals became extinct. The giant sloth, woolly rhinoceros, cave lion, saber-toothed tiger, and many others all died out. This was also the end of the woolly mammoth.
For many years scientists suspected that humankind's ancestors were responsible for hunting these animals to extinction. But scientists now believe that climate change was also partly responsible. The warming temperatures at the end of the last ice age led to a change in the species of plants available for food. The combination of rising temperatures and different plants was too difficult for the giant herbivores to adapt to.
There was one notable and strange exception, however. Some woolly mammoths survived on the small and remote Wrangel Island in the Russian Arctic until approximately 1700 BC. The island was too small to support a large number of full-size mammoths, but a population of dwarf mammoths survived there. To this day Wrangel Island supports a greater number of Arctic plants than any other place on the planet of similar size. It's intriguing to think that in 2000 BC, when the great pyramids were being built in Egypt, woolly mammoths still wandered the plains.
Most of what we know about mammoths comes from the study of frozen carcasses found in northern Siberia. Only a few dozen mammoth remains have been found, and bodies that are complete are very rare. But unlike the fossil and skeleton remains of other extinct species, the frozen remains of mammoths allow scientists to study their skin, flesh, and sometimes their internal organs.
Some scientists are investigating ways to bring the woolly mammoth back to life. One proposal involves extracting frozen sperm from a preserved mammoth's reproductive organs, and using it to fertilize the egg of a female elephant. Another method would be to clone the animal. Scientists would have to extract DNA from a piece of a preserved mammoth carcass, then replace the DNA of an elephant's egg with the mammoth's DNA. Scientists would stimulate the egg to start growing and place it inside a female elephant for the duration of the gestation period.
There are problems with both of these techniques. Even under laboratory conditions, it is hard for egg and sperm cells to survive freezing. Furthermore, if intact sperm cells from a woolly mammoth could be found, using them to fertilize an elephant egg would not bring the mammoth back to life. Instead it would create an animal that is a hybrid of the woolly mammoth and the elephant. Cloning is a more promising method. For many years the idea of cloning a mammoth seemed ridiculous because DNA from a frozen carcass is typically fragmented. But recently geneticists have made progress analyzing fragmented DNA, and a significant portion of mammoth DNA has been reassembled. It may take many years, but one day scientists may clone the long-dead cousin to the elephant, and the woolly mammoth will walk the earth again.