The musk deer (Moschidae) of Asia and chevrotains (Tragulidae) of tropical African and Asian forests are separate families that are also in the ruminant clade Ruminantia; they are not especially closely related to Cervidae.

[4] For many types of deer in modern English usage, the male is a buck and the female a doe, but the terms vary with dialect, and according to the size of the species.

There are also several species of deer that are highly specialized and live almost exclusively in mountains, grasslands, swamps, and "wet" savannas, or riparian corridors surrounded by deserts.

The White-tailed deer have recently expanded their range within the foothills and river valley bottoms of the Canadian Rockies owing to conversion of land to cropland and the clearing of coniferous forests allowing more deciduous vegetation to grow up the mountain slopes.

"European" fallow deer historically lived over much of Europe during the Ice Ages, but afterwards became restricted primarily to the Anatolian Peninsula, in present-day Turkey.

As a result of acclimatisation society releases in the 19th century, Australia has six introduced species of deer that have established sustainable wild populations.

[9] Though of a similar build, deer are strongly distinguished from antelopes by their antlers, which are temporary and regularly regrown unlike the permanent horns of bovids.

[15] Antler development begins from the pedicel, a bony structure that appears on the top of the skull by the time the animal is a year old.

Deer are browsers, and feed primarily on foliage of grasses, sedges, forbs, shrubs and trees, secondarily on lichens in northern latitudes during winter.

The deer require a large amount of minerals such as calcium and phosphate in order to support antler growth, and this further necessitates a nutrient-rich diet.

There are some reports of deer engaging in carnivorous activity, such as eating dead alewives along lakeshores[48] or depredating the nests of northern bobwhites.

[54] The white-tailed deer Odocoileus virginianus has been confirmed as the sole maintenance host in the Michigan outbreak of bovine tuberculosis which remains a significant barrier to the US nationwide eradication of the disease in livestock.

Out of an abundance of caution hunters are advised to avoid contact with specified risk material (SRM) such as the brain, spinal column or lymph nodes.

[65] Another contemporaneous form was the four-horned protoceratid Protoceras, that was replaced by Syndyoceras in the Miocene; these animals were unique in having a horn on the nose.

[58] Late Eocene fossils dated approximately 35 million years ago, which were found in North America, show that Syndyoceras had bony skull outgrowths that resembled non-deciduous antlers.

The tribe Muntiacini made its appearance as † Muntiacus leilaoensis around 7–8 Mya;[72] The early muntjacs varied in size–as small as hares or as large as fallow deer.

[73] Around this period, the Tethys Ocean disappeared to give way to vast stretches of grassland; these provided the deer with abundant protein-rich vegetation that led to the development of ornamental antlers and allowed populations to flourish and colonise areas.

[73] This implies the Bering Strait could be crossed during the late Miocene–Pliocene; this appears highly probable as the camelids migrated into Asia from North America around the same time.

[77] Deer invaded South America in the late Pliocene (2.5–3 Mya) as part of the Great American Interchange, thanks to the recently formed Isthmus of Panama, and emerged successful due to the small number of competing ruminants in the continent.

[78] Large deer with impressive antlers evolved during the early Pleistocene, probably as a result of abundant resources to drive evolution.

[87] Molecular phylogenetic analyses since the latter half of the 2000s all show that hydropotes is a sister taxon of Capreolus, and “Hydropotinae” became outdated subfamily.

Then a phylogenetic study by Alexandre Hassanin (of National Museum of Natural History, France) and colleagues, based on mitochondrial and nuclear analyses, revealed that Moschidae and Bovidae form a clade sister to Cervidae.

The 2006 study identified two lineages in Cervinae, Cervini (comprising the genera Axis, Cervus, Dama and Rucervus) and Muntiacini (Muntiacus and Elaphodus).

In the Upper Palaeolithic, the reindeer was the staple food for Cro-Magnon people,[94] while the cave paintings at Lascaux in southwestern France include some 90 images of stags.

Coats of arms featuring deer include those of Baden-Württemberg, Dotternhausen, Thierachern, Friolzheim, Bauen, Albstadt, and Dassel in Germany; of the Earls Bathurst in England;[105] of Balakhna,[106] Gusev,[107] Nizhny Novgorod,[108] Odintsovo,[109] Slavsk[110] and Yamalo-Nenets[111] in Russia; of Berezhany, Sambir in Ukraine; of Åland,[112] Finland; of Gjemnes,[113] Hitra,[114] Hjartdal[115] and Rendalen[116] in Norway; of Jelenia Góra,[117] Poland; of Umeå,[118] Sweden; of Queensland,[119] Australia; of Cervera,[120] Catalonia; of Selonia[121] and Semigallia[122] in Latvia; and of Chile.

Deer hunting is a popular activity in the U.S. that can provide the hunter's family with high quality meat and generates revenue for states and the federal government from the sales of licenses, permits and tags.

Fish and Wildlife Service estimates that big game hunting for deer and elk generates approximately $11.8 billion annually in hunting-related travel, equipment and related expenditures.

The Sami of Scandinavia and the Kola Peninsula of Russia and other nomadic peoples of northern Asia use reindeer for food, clothing, and transport.

They compete with livestock for resources, as well as cause excess erosion and wreak havoc on wild plant species and agriculture alike.

They can also have an effect on the conservation efforts of other plant and animal species, as they can critically offset the balance within an environment by drastically depleting diversity within forests.