However, behaviour which enhances the fitness of relatives but lowers that of the actor, may nonetheless increase in frequency. Relatives do, by definition, carry many of the same genes. This is the fundamental principle behind the theory of kin selection. According to the theory, the enhanced fitness of relatives may more than compensate for the fitness loss of the helpers (individuals displaying the behaviour).
This is a special case of a more general model, called inclusive fitness.
Hamilton's equation describes whether or not a gene for helping behaviour will spread in a population. The gene will spread if rxb is greater than c:
where:
Sterile
Sterile is an important term which has two main meanings.
1. Anything which is not infected by bacteria (or viruses or parasites).
2. Unable to give rise to offspring (children) by birth or fertilisation.
Foraging
Foraging is the act of hunting or gathering food. For example, cattle forage grass to eat. The idea of animals foraging is called "forage theory", and was first proposed in 1966.
Humans that forage are often called hunter-gatherers, who find and eat (wild) animals and plants without domestication of them (people who farm plants are not hunter-gatherers, as they have grown them themselves).
Pacific Northwest
The Pacific Northwest, also referred to as Cascadia, is a region on the west coast of North America. It refers to the northwestern corner of the United States and the southwestern part of Canada. The U.S. states of Washington, Idaho, western Montana, Oregon and northern California are in the southern part of the Pacific Northwest. The Canadian province of British Columbia and the southeastern part of the U.S. state of Alaska is in the northern part. The entire region is bordered by the Pacific Ocean to the west.
Historically, the Pacific Northwest had many Native Americans. Starting from about 15,000 years ago, Native Americans settled along the coastline and along the major rivers. From the 1500s to the 1700s, Europeans explored the region, beginning with the discovery of Oregon and Washington. In the early 1800s, the famous Lewis and Clark expedition arrived in Washington State. From the 19th century to present day, the region began to become settled. Today, the largest cities in the Northwest include Vancouver, Seattle and Portland.
The rugged mountains of the Northwest consist of the Coast Range, which is nearer the coast, and the Cascade Range. In northern Washington, the Cascade Range is called the North Cascades. In British Columbia, it is called the Canadian Cascades. The many rivers of the Northwest result from its wet climate - the mountains trap wet Pacific air, leaving little rain for inland states like Idaho. The rivers once supported large salmon runs, but large power dams have been built on many rivers.
The main language of the Pacific Northwest is English in the United States and Canada; among the Native Americans Chinook Jargon is common. Among the many Asian immigrants, Chinese is being used more in the Northwest.
The Pacific Northwest basically extends from southeastern Alaska to Northern California. Along this entire length, is a large mountain range, the Cascade Range, that forms the geographic spine of the Pacific Northwest. The highest mountain in the Northwest is Mount Rainier. Rainier is high. Other notable mountains include Mount Shasta, at , and Mount Baker, at . East of the Cascades, there is the Columbia Plateau, a high area of land that stretches east to the Rocky Mountains in Idaho and Montana. In the west, the Coast Range borders the coast more closely. The Olympic Mountains are on the Olympic Peninsula, an extension of Washington State. Puget Sound is a large system of bays and straits in northwestern Washington and southeastern British Columbia.
The main rivers of the Pacific Northwest are the Fraser River, the Columbia River, and the Snake River. The Fraser River is mainly in British Columbia; it flows west to the Pacific Ocean near Vancouver. The Fraser drains most of the southern Canadian Cascades. The Columbia River begins in the Canadian Cascades and flows south, then turns west where it meets the Snake River. From there, it flows on to the ocean near Portland. The Snake River is mainly in inland Idaho. After a journey west from the Rocky Mountains, it meets the Columbia at Kennewick, Washington.
Other rivers in the Northwest include the Finlay, the Skagit, the Umpqua, the Rogue, and the Klamath. The Finlay drains the northern Canadian Cascades and flows on to join the Mackenzie River, which flows through Canada to Hudson Bay. The Skagit also begins in the Canadian Cascades, and crosses into Washington; it turns west and flows into the sea north of Everett, Washington. The Umpqua River begins in the Southern Oregon Cascades, and flows west to the Pacific Ocean near Reedsport, Oregon. The Rogue parallels the Umpqua and dumps into the sea at Gold Beach, Oregon. The Klamath flows south from a valley in inland Oregon, then turns west through northern California, cutting through the Cascade Range to its mouth near Klamath, California.
Adaptation
Adaptation is the evolutionary process where an organism becomes better suited to its habitat. This process takes place over many generations. It is one of the basic phenomena of biology.
When people speak about adaptation, they often mean a 'feature' (a trait) which helps an animal or plant survive. An example is the adaptation of horses' teeth to grinding grass. Grass is their usual food; it wears the teeth down, but horses' teeth continue to grow during life. Horses also have adapted to run fast, which helps them to escape their predators, such as lions. These features are the "product" of the process of adaptation.
The illustration of bird beaks shows an obvious sign of their different ways of life. However, eating a different food also means having a different digestive system, gut, claws, wings and above all, different inherited behaviour. For the major adaptations, what changes is not a single trait, but a whole group of features.
Adaptation occurs because the better adapted animals are the most likely to survive, and to reproduce successfully. This process is known as natural selection; it is the basic cause of evolutionary change.
Adaptation is, first of all, a "process", rather than a physical part of a body.
Adaptation... could no longer be considered a static condition, a product of a creative past, and became instead a continuing dynamic process. "Ernst Mayr".
An internal parasite (such as a fluke) is a good example: it has a very simple bodily structure, but still the organism is highly adapted to its particular environment. From this we see that adaptation is not just a matter of visible traits: in such parasites critical adaptations take place in the life cycle, which is often quite complex.
However, as a practical term, adaptation is often used for the "product": those features of a species which result from the process. Many aspects of an animal or plant can be correctly called adaptations, though there are always some features whose function is in doubt. By using the term "adaptation" for the evolutionary "process", and "adaptive trait" for the bodily part or function (the product), the two senses of the word may be distinguished.
Adaptation is one of the two main processes that explain the diverse species we see in biology. The other is speciation (species-splitting or cladogenesis). A favourite example used today to study the interplay of adaptation and speciation is the evolution of cichlid fish in African lakes.
An organism must be viable at all stages of its development and at all stages of its evolution. This places "constraints" on the evolution of development, behaviour and structure of organisms.