The grizzly bear is a subspecies of the brown bear (Ursus arctos). The grizzly bear life cycle begins with a baby bear that is a helpless furless ball but it can grow to become a feared and powerful predator, able to dispatch animals as large as moose and elk with a single blow.

The female grizzly bear will mate with several males if enough are in the area she inhabits. For most grizzly bears, mating season runs from May into the first part of June. The female becomes sexually mature and able to have cubs between 4 1/2 and 10 years of age. Most females will breed once every three to four years, as it requires a few years to integrate their cubs into the world.

The bear gestation period varies between 180 and 266 days. The embryo’s development goes on hold temporarily at first, as the female gorges herself on whatever foods are available during the summer and autumn to develop a layer of fat off to live on through the winter months. The female chooses the site of her den, often under a log, in a cave or in a hollow tree. She will then proceed to enter a sort of stupor that is not a true hibernation, with her body temperature, heart rate and breathing all reduced. Once she is in this state, the embryo starts to develop once more, with the female giving birth to one to four cubs no later than March.

The newborn cub lacks fur and cannot see until it's a few days old. Although the young cease suckling from the mother by about the age of five months, they will continue to stay with her for as long as three years. The cubs need her protection from predators such as other bears, cougars and wolves. The grizzly cub has the ability to climb trees with ease until it is about a year old. The mother provides the meals with her foraging and hunting skills.

Once the cubs are capable of fending for themselves, the mother will drive them away from her and look to breed again. By this time the young grizzly weighs between 350 to 700 lbs and is close to the weight of a full grown grizzly bear. A bear's weight is dependent on the abundance of food. As these bears grow in size and strength, their diet will expand as they start to possess the ability to kill larger prey. These male grizzlies will wait until they reach their sexual maturity before they breed, with some mature at 4 years old and others needing as much as 18 more months to reach full adulthood. In the meantime, they will establish their own territories as they age.

One grizzly in captivity lived to be 47 years old. This is far from the norm for those in the wild. The typical grizzly bear lifespan is generally 15 to 20 years in the wild, with some making it to 25.