All eight of the species of bears living today had a common ancestor, Ursavus, that lived during the Miocene period over 20 million years ago. The evolutionary routes (phylogeny) that bears took to reach their present positions make an interesting story, which will undoubtedly change as new evidence becomes available.  Two lines of evidence for bear phylogeny are presently available: paleontological (fossil) and molecular. Both sets of data are in general agreement as to the timing of speciation (the formation of new species) events. The fossil data suggest that Ursavus and his relatives were forest-dwelling carnivores that probably lived much as foxes or raccoons do today. They had warm fur coats that enabled them to live in cool climates with cold winters. They ate meat, but probably also fed on a variety of plant foods, especially when prey was not available. Their teeth were primarily the teeth of carnivores; sharp, cutting teeth adapted for tearing and ripping, but they were beginning to develop teeth for grinding plant foods. During winter periods, they were probably restricted to areas where their prey could also survive.

The evolutionary process has been at work shaping the animals we call bears for over 20 million years. The formation of new species is a continuous process that takes place over long periods of time. Generally a new species is formed from a population of animals after they become isolated from other populations of the species. At some point, after about half a million years or so, the isolated population becomes so different genetically that it is unable to reproduce with its parent population, which has also diverged over time. This is called reproductive isolation.

Many groups of animals that we all would consider to be distinct species are actually able to breed successfully with other species on a physiological and genetic basis. In some cases they are prevented from doing so because they have developed distinct breeding behaviors which keep them from 'recognizing' the other species and consummating the reproductive act. This is called behavioral isolation.

In other cases they are separated by geographic barriers that effectively prevent any individuals from the two groups from coming in contact with each other. If this geographic isolation lasts long enough, they may become behaviorally or reproductively isolated, or both. Grizzly bears and polar bears are a case in point. Their genetic lineages diverged less than one million years ago according to the evidence of mitochondrial DNA. They have produced viable offspring from matings in zoos; in one case a male polar bear accidentally got into an enclosure with a female Kodiak bear at the U.S. National Zoo in 1936. They mated and had three hybrid offspring. A breeding experiment was then conducted and the hybrid offspring proved able to breed successfully with each other, indicating that these two species of bears were much more closely related than previously expected. In fact all the species in the subfamily Ursinae (all bears except the giant panda and the spectacled bear) probably have the ability to crossbreed, and several combinations have actually occurred.

Bears and Humans

Humans and bears coexisted until technologies arose to give humans an advantage.  As human populations have grown, people have required more space.  In the competition for space humans are now easily able to exclude bears and other species from the land.  This has happened fast enough to drive species to extinction and to threaten them even in protected areas. Small populations tend to go extinct. If an entire species is reduced to one small population, the entire species will almost certainly wink out of existence, never to return. In the early 70's scientists introduced a systems approach to the study of extinction, distinguishing between deterministic (caused) and stochastic (random) factors. 

These ideas were further refined so that now it is understood that the primary factors affecting the survival of small populations are: (1) deterministic extinction, which occurs when something essential is removed (such as space, shelter, or food) or when something that has negative effects (like a competing exotic species or a disease) is introduced, (2) environmental stochasticity, or random changes in the environment such as drought, global warming, or severe winters, (3) demographic stochasticity, or the chance variation in individual birth and death (demographic) events, which has very large effects once a population becomes very small, (4) genetic deterioration, which can reduce fitness through increased genetic drift, inbreeding, and the subsequent loss of heterozygosity and genetic variance, and (5) catastrophes, or rare but widespread events that can extinguish a population or species, such as a huge meteorite, an epic flood, or the eruption of a large volcano.

Loss of habitat and fragmentation are the immediate threat to bears today. Fragmentation of bear habitat and small bear population sizes are the result of centuries of competition with human beings. Once a population becomes small (less than 100 animals) the stochastic or random factors become much more important. Although populations tend to become extinct from the direct random processes of small populations such as few females of breeding age, inability to find a mate etc., those demographic effects are made worse by genetic effects.

Bear Conservation 

Due to their intolerance of human beings and utilization of diverse foods over large areas grizzly bears require specific considerations when developing a conservation design for a region. These characteristics also make the grizzly bear a good choice as an ‘umbrella species’ – a species whose needs are co-incident with many others species and thereby provides an Umbrella of protection. Although grizzly bears are intelligent, adaptable animals, their survival is dependent upon their ability tohigh quality food find sources.Contacts with human beings for any reason increases the probability that the bear will be killed.Basically, bears need areas where they can find good quality food without being killed by humans.

Predators such as bears are just the tip of the iceberg; we are losing populations of plants and animals at alarming rates.In one sense this is a moral and spiritual failure on our part. On a more practical level what we are ultimately losing is information.We are losing information on how life operates.We are losing data and systems that capture energy from the sun and pass it along to support species and ecosystems; and one of those species is us.We need to keep the systems intact so that we can continue to lead healthy, interesting lives.We need to keep the information intact because it could be very important for us at sometime in the future.If we lose genetic and ecological information, from almost any plant or animal, we are reducing our own options.

The maintenance of large conservation networks (the science of Conservation Area Design) requires a degree of sacrifice by humans.  We must be willing to give up some areas for other species to survive.  This is what saving the rainforest, or saving the desert tortoise, or saving the bears, is all about.  It is not an unrewarded sacrifice however; it is essential to maintaining our current quality of life, and of improving the quality of life for others.  If we reduced the natural world to monocultures of a few agricultural plants, and a few domesticated animals, we would have very few options in the face of environmental change.  To feed human populations and to support our civilizations however, we need these simplified agricultural systems, at least until we devise more complex ones.  The critical balance that society needs to find now is how to maintain the function of natural systems at the same time and in the same areas, that we maintain our own domestic systems.

We need to maintain this balance; between the immediate needs of human beings, and the long-term needs of natural systems including humans. Visions to do this must cut across many artificial human boundaries and be based on the ecological and evolutionary networks we need to maintain. Borders and boundaries are irrelevant to gene flow, nutrient cycling, or seed propagation. Such visions have primarily been formulated by independent scientists and non-governmental organizations. However, as the science progresses, and as government agencies develop cooperative strategies, interagency approaches are also beginning to develop conservation area design strategies.

In the U.S., visions such as The Wildlands Project and the the Yukon-to-Yellowstone Conservation Initiative have developed on a local basis by groups and individuals that work on areas where they live.These are projects designed to improve or maintain natural ecosystems, native species, and air and water quality by protecting core areas of wildlife habitat and habitat connections within the matrix of human-altered landscapes. They are projects designed to maintain human options as well as maintaining options for other species. Based upon core areas that are already protected as national parks and wilderness areas, scientists are working to determine what additional areas, if any, are needed in order to maintain viable populations of large carnivores such as bears. If large carnivore populations are preserved, then most other native animals and plants will also be protected. This applies to other species than bears, and applies to all ecosystems on the planet. The best hope for preserving species is to provide habitat. The best way to provide more habitat where it is fragmented into isolated patches is to connect the patches somehow so that animals can move between them. The best thing that individuals can do to promote conservation is to tolerate wildlife nearby, avoid attracting them to areas where they will cause conflicts, understand their needs, and give them the space they need.