Phylogenetics in the context of "Evolution of the horse"

Biodiversity is the variability of life on Earth. It can be measured on various levels, for example, genetic variability, species diversity, ecosystem diversity and phylogenetic diversity. Diversity is not distributed evenly on Earth—it is greater in the tropics as a result of the warm climate and high primary productivity in the region near the equator. Tropical forest ecosystems cover less than one-fifth of Earth's terrestrial area and contain about 50% of the world's species. There are latitudinal gradients in species diversity for both marine and terrestrial taxa.

Since life began on Earth, six major mass extinctions and several minor events have led to large and sudden drops in biodiversity. The Phanerozoic aeon (the last 540 million years) marked a rapid growth in biodiversity via the Cambrian explosion. In this period, the majority of multicellular phyla first appeared. The next 400 million years included repeated, massive biodiversity losses. Those events have been classified as mass extinction events. In the Carboniferous, rainforest collapse may have led to a great loss of plant and animal life. The Permian–Triassic extinction event, 251 million years ago, was the worst; vertebrate recovery took 30 million years.

Charles Robert Darwin (/ˈdɑːrwɪn/ DAR-win; 12 February 1809 – 19 April 1882) was an English naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all species of life have descended from a common ancestor is now generally accepted and considered a fundamental scientific concept. In a joint presentation with Alfred Russel Wallace, he introduced his scientific theory that this branching pattern of evolution resulted from a process he called natural selection, in which the struggle for existence has a similar effect to the artificial selection involved in selective breeding. Darwin has been described as one of the most influential figures in human history and was honoured by burial in Westminster Abbey.

Darwin's early interest in nature led him to neglect his medical education at the University of Edinburgh; instead, he helped Grant to investigate marine invertebrates. His studies at the University of Cambridge's Christ's College from 1828 to 1831 encouraged his passion for natural science. However, it was his five-year voyage on HMS Beagle from 1831 to 1836 that truly established Darwin as an eminent geologist. The observations and theories he developed during his voyage supported Charles Lyell's concept of gradual geological change. Publication of his journal of the voyage made Darwin famous as a popular author. His first scientific work was The Structure and Distribution of Coral Reefs (1842). Along with his work on barnacles, it won him the Royal Medal in 1853.

Eumetazoa (from Ancient Greek εὖ (eû) 'well' μετά (metá) 'after' and ζῷον (zôion) 'animal'), also known as Epitheliozoa or Histozoa, is a proposed basal animal subkingdom as a sister group of Porifera (sponges). The basal eumetazoan clades are the Ctenophora and the ParaHoxozoa. Placozoa is now also seen as a eumetazoan in the ParaHoxozoa. The competing hypothesis is the Myriazoa clade. The subkingdom Parazoa and Agnotozoa are the other taxa, and agnotozoa may be fake or even nonexistent at studies. Parazoa or Agnotozoa are a main sister group to eumetazoans, forming clade Blastozoa/Diploblastozoa. Alternatively,Parazoa was considered as a sister group to Agnotozoa (now considered polyphyletic).Several other extinct or obscure life forms, such as Iotuba and Thectardis, appear to have emerged in the group. Characteristics of eumetazoans include true tissues organized into germ layers, the presence of neurons and muscles, and an embryo that goes through a gastrula stage.

Some phylogenists once speculated the sponges and eumetazoans evolved separately from different single-celled organisms, which would have meant that the animal kingdom does not form a clade (a complete grouping of all organisms descended from a common ancestor). However, genetic studies and some morphological characteristics, like the common presence of choanocytes, now unanimously support a common origin.

A fish is an aquatic, anamniotic, gill-bearing vertebrate animal with swimming fins and a hard skull, but lacking limbs with digits. Fish can be grouped into the more basal jawless fish and the more common jawed fish, the latter including all living cartilaginous and bony fish, as well as the extinct placoderms and acanthodians. In a break from the long tradition of grouping all fish into a single class (Pisces), modern phylogenetics views fish as a paraphyletic group which includes all vertebrates except tetrapods. In English, the plural of "fish" is fish when referring to individuals and fishes when referring to species.

Most fish are cold-blooded, their body temperature varying with the surrounding water, though some large, active swimmers like the white shark and tuna can maintain a higher core temperature. Many fish can communicate acoustically with each other, such as during courtship displays. The study of fish is known as ichthyology.

Zoogeography is the branch of the science of biogeography that is concerned with geographic distribution (present and past) of animal species.

As a multifaceted field of study, zoogeography incorporates methods of molecular biology, genetics, morphology, phylogenetics, and Geographic Information Systems (GIS) to delineate evolutionary events within defined regions of study around the globe. As proposed by Alfred Russel Wallace, known as the father of zoogeography, phylogenetic affinities can be quantified among zoogeographic regions, further elucidating the phenomena surrounding geographic distributions of organisms and explaining evolutionary relationships of taxa.

Plankton are organisms that drift in water (or air) but are unable to actively propel themselves against currents (or wind). Marine plankton include drifting organisms that inhabit the saltwater of oceans and the brackish waters of estuaries. Freshwater plankton are similar to marine plankton, but are found in lakes and rivers. An individual plankton organism in the plankton is called a plankter. In the ocean plankton provide a crucial source of food, particularly for larger filter-feeding animals, such as bivalves, sponges, forage fish and baleen whales.

Plankton includes organisms from species across all the major biological kingdoms, ranging in size from the microscopic (such as bacteria, archaea, protozoa and microscopic algae and fungi) to larger organisms (such as jellyfish and ctenophores). This is because plankton are defined by their ecological niche and level of motility rather than by any phylogenetic or taxonomic classification. The plankton category differentiates organisms from those that can swim against a current, called nekton, and those that live on the deep sea floor, called benthos. Organisms that float on or near the water's surface are called neuston. Neuston that drift as water currents or wind take them, and lack the swimming ability to counter this, form a special subgroup of plankton. Mostly plankton just drift where currents take them, though some, like jellyfish, swim slowly but not fast enough to generally overcome the influence of currents.

Human anatomy (gr. ἀνατομία, "dissection", from ἀνά, "up", and τέμνειν, "cut") is primarily the scientific study of the morphology of the human body. Anatomy is subdivided into gross anatomy and microscopic anatomy. Gross anatomy (also called macroscopic anatomy, topographical anatomy, regional anatomy, or anthropotomy) is the study of anatomical structures that can be seen by the naked eye. Microscopic anatomy is the study of minute anatomical structures assisted with microscopes, which includes histology (the study of the organization of tissues), and cytology (the study of cells). Anatomy, human physiology (the study of function), and biochemistry (the study of the chemistry of living structures) are complementary basic medical sciences that are generally together (or in tandem) to students studying medical sciences.

In some of its facets human anatomy is closely related to embryology, comparative anatomy and comparative embryology, through common roots in evolution; for example, much of the human body maintains the ancient segmental pattern that is present in all vertebrates with basic units being repeated, which is particularly obvious in the vertebral column and in the ribcage, and can be traced from very early embryos.

Guinea fowl (/ˈɡɪnifaʊl/) are birds of the family Numididae in the order Galliformes. They are endemic to Africa and rank among the oldest of the gallinaceous birds. Phylogenetically, they branched off from the core Galliformes after the Cracidae (chachalacas, guans, and curassows) and before the Odontophoridae (New World quail). An Eocene fossil lineage Telecrex has been associated with guinea fowl; Telecrex inhabited Mongolia, and may have given rise to the oldest of the true phasianids, such as blood pheasants and eared pheasants, which evolved into high-altitude, montane-adapted species with the rise of the Tibetan Plateau. While modern guinea fowl species are endemic to Africa, the helmeted guinea fowl has been introduced as a domesticated bird widely elsewhere.