From flying squirrels to grizzly bears, and from torpid turtles to insects with antifreeze, the animal kingdom relies on some staggering evolutionary innovations to survive winter. Unlike their human counterparts, who must alter the environment to accommodate physical limitations, animals are adaptable to an amazing range of conditions. Examining everything from food sources in the extremely barren winter land-scape to the chemical composition that allows certain creatures to survive, Heinrich's Winter World awakens the largely undiscovered mysteries by which nature sustains herself through winter's harsh, cruel exigencies. From flying squirrels to grizzly bears, and from torpid turtles to insects with antifreeze, the animal kingdom relies on some staggering evolutionary innovations to survive winter. Unlike their human counterparts, who must alter the environment to accommodate physical limitations, animals are adaptable to an amazing range of conditions. Examining everything from food sources in the extremely barren winter land-scape to the chemical composition that allows certain creatures to survive, Heinrich's Winter World awakens the largely undiscovered mysteries by which nature sustains herself through winter's harsh, cruel exigencies. BERND HEINRICH is an acclaimed scientist and the author of numerous books, including the best-selling  Winter World, Mind of the Raven, Why We Run, The Homing Instinct, and One Wild Bird at a Time.  Among Heinrich's many honors is the 2013 PEN New England Award in nonfiction for  Life Everlasting.  He resides in Maine. Winter World The Ingenuity of Animal Survival By Bernd Heinrich HarperCollins Publishers, Inc. Copyright © 2009 Bernd Heinrich All right reserved. ISBN: 9780061129070 Chapter One Fire and Ice Microscopic life evolved some 3.5 billion years ago in the Precambrian period during the first and longest chapter of life that covers about 90 percent of geological time. No one knows exactly what the earth was like when microbial life began but we do know that at some time the earth was a hot and hellish place with an atmosphere that lacked oxygen. Early microbes, probably bluegreen algae or bacterialike organisms, invented photosynthesis to harness sunlight as a source of energy. They took carbon dioxide out of the air as their food, and they generated oxygen as a waste product that further transformed the atmosphere and hence the climate. They developed DNA for storing information, invented sex, which produced variation for natural selection, and evolution took off on its unending and largely unpredictable course. Molecular fingerprinting suggests that every life-form on earth today originated from the same bacterialike ancestor. That ancestor eventually led to the three main surviving branches of life, the archaea, bacteria, and the eukaryotes (the organisms made of cells with a nucleus that include algae, plants, fungi, and animals). Remnants of the first ancient pre-oxygen-using life may still exist little-changed today. They are thought to be sulphur-consuming bacteria now living only in the few remaining places where the ancient and to us hellish conditions still remain. These habitats include hot springs and deep oceanic thermal vents where water at 300°C (that stays liquid there rather than turning to steam because it is under intense pressure in depths of some 3,600 meters) issues up from the ocean floor. One of the species living at the edge of these hot water vents is Pyrolobus fumarii , which can't grow unless heated to at least 90°C, and which it tolerates 113°C. As the earth cooled new environments became available and new single-celled and then multicelled organisms evolved from these or similar species to invade ever-new and cooler environments. Some cells much later also escaped their ancestral conditions by invading other cells, finding that environment conducive for survival and adapting to it. Such initially parasitic organisms ultimately evolved into cooperative or symbiotic relationships with their hosts. Perhaps the most fateful of these eventually mutually beneficial associations occurred when some Precambrian green algae successfully grew inside other cells, to ultimately become chloroplasts, while their hosts then became green plants . The ability to capture solar energy that ushered in the multicellular life and the fantastic diversity of life we see today was followed by or concurrent with one other critical parasitic-turned-symbiotic cellular invasion. The availability of oxygen from plants led to energy and oxygen-guzzling bacteria, and when some of these invaded other cells they became mitochondria and their hosts became animals. Mitochondria are the cell's source of power or energy-use, and having mitochondria with access to oxygen allowed vastly greater rates of energy expenditure. It made the evolution of multicellular animals possible. One of the ultimate expressions of the high-energy way of life that i