Genetic diversity

Genetic diversity is a level of biodiversity that refers to the total number of genetic characteristics in the genetic makeup of a specie. It is distinguished from genetic variability, which describes the tendency of genetic characteristics to vary.:)

The academic field of population genetics includes several hypotheses regarding genetic diversity. The neutral theory of evolution proposes that diversity is the result of the accumulation of neutral substitutions. Diversifying selection is the hypothesis that two subpopulations of a species live in different environments that select for different alleles at a particular locus. This may occur, for instance, if a species has a large range relative to the mobility of individuals within it. Frequency-dependent selection is the hypothesis that as alleles become more common, they become less fit. This is often invoked in host-pathogen interactions, where a high frequency of a defensive allele among the host means that it is more likely that a pathogen will spread if it is able to overcome that allele.

Ruminantia

The biological suborder Ruminantia includes many of the well-known large grazing or browsing mammals: among them cattle, goats, sheep, deer, and antelope. All members of the Ruminantia are ruminants: they digest food in two steps, chewing and swallowing in the normal way to begin with, and then regurgitating the semi-digested cud to re-chew it and thus extract the maximum possible food value.

Note that not all ruminants belong to the Ruminantia. Camels and llamas are among the exceptions, a suborder known as Tylopoda. Also, there are a number of other large grazing mammals that, while not strictly ruminants, have similar adaptations for surviving on large quantities of low-grade food. Kangaroos and horses are examples.

Landlocked seas

• Aral Sea
• Lake Balkhash
• Caspian Sea
• Lake Chad
• Lake Chilwa
• Chott Melrhir
• Dead Sea
• Lake Eyre
• Issyk Kul
• Namtso
• Sea of Galilee
• Great Salt Lake
• Qinghai Lake
• Salton Sea
• Tonle Sap
• Lake Torrens
• Lake Turkana
• Lake Van

Leather

Leather is a material created through the tanning of hides and skins of animals, primarily cattlehide. The tanning process converts the putrescible skin into a durable, long-lasting and versatile natural material for various uses.

Together with wood, leather formed the basis of much ancient technology. The leather industry and the fur industry are distinct industries that are differentiated by the importance of their raw materials. In the leather industry the raw materials are by-products of the meat industry, with the meat having higher value than the skin. The fur industry uses raw materials that are higher in value than the meat and hence the meat is classified as a by-product. Taxidermy also makes use of the skin of animals, but generally the head and part of the back are used. Hides and skins are also used in the manufacture of glue and gelatin

Chesapeake Bay impact crater

The Chesapeake Bay impact crater was formed by a bolide that impacted the eastern shore of North America about 35.5 million years ago, in the late Eocene epoch. It is one of the best-preserved "wet-target" or marine impact craters, and the largest impact crater in the U.S. Continued slumping of sediments over the rubble of the crater have helped shape Chesapeake Bay.