Homo habilis is an extinct species of archaic human from the Early Pleistocene of East and South Africa about 2.3 million years ago to 1.65 million years ago (mya). Upon species description in 1964, H. habilis was highly contested, with many researchers recommending it be synonymised with Australopithecus africanus, the only other early hominin known at the time, but H. habilis received more recognition as time went on and more relevant discoveries were made. By the 1980s, H. habilis was proposed to have been a human ancestor, directly evolving into Homo erectus, which directly led to modern humans. This viewpoint is now debated. Several specimens with insecure species identification were assigned to H. habilis, leading to arguments for splitting, namely into "H. rudolfensis" and "H. gautengensis" of which only the former has received wide support.
Sexual selection is a mechanism of evolution in which members of one biological sex choose mates of the other sex to mate with, and compete with members of the same sex for access to members of the opposite sex. These two forms of selection mean that some individuals have greater reproductive success than others within a population, for example because they are more attractive or prefer more attractive partners to produce offspring. Successful males benefit from frequent mating and monopolizing access to one or more fertile females. Females can maximise the return on the energy they invest in reproduction by selecting and mating with the best males.
Sex is the biological trait that determines whether a sexually reproducing organism produces male or female gametes. During sexual reproduction, a male and a female gamete fuse to form a zygote, which develops into an offspring that inherits traits from each parent. By convention, organisms that produce smaller, more mobile gametes are called male, while organisms that produce larger, non-mobile gametes are called female. An organism that produces both types of gamete is hermaphrodite.
Birds of prey or predatory birds, also known as raptors, are hypercarnivorous bird species that actively hunt and feed on other vertebrates. In addition to speed and strength, these predators have keen eyesight for detecting prey from a distance or during flight, strong feet with sharp talons for grasping or killing prey, and powerful, curved beaks for tearing off flesh. Although predatory birds primarily hunt live prey, many species also scavenge and eat carrion.
Sexual dimorphism is the condition where sexes of the same species exhibit different morphological characteristics, including characteristics not directly involved in reproduction. The condition occurs in most dioecious species, which consist of most animals and some plants. Differences may include secondary sex characteristics, size, weight, color, markings, or behavioral or cognitive traits. Male-male reproductive competition has evolved a diverse array of sexually dimorphic traits. Aggressive utility traits such as "battle" teeth and blunt heads reinforced as battering rams are used as weapons in aggressive interactions between rivals. Passive displays such as ornamental feathering or song-calling have also evolved mainly through sexual selection. These differences may be subtle or exaggerated and may be subjected to sexual selection and natural selection. The opposite of dimorphism is monomorphism, when both biological sexes are phenotypically indistinguishable from each other.
Waders or shorebirds are birds of the order Charadriiformes commonly found wading along shorelines and mudflats in order to forage for food crawling or burrowing in the mud and sand, usually small arthropods such as aquatic insects or crustaceans. The term "wader" is used in Europe, while "shorebird" is used in North America, where "wader" may be used instead to refer to long-legged wading birds such as storks and herons.
The Bovidae comprise the biological family of cloven-hoofed, ruminant mammals that includes cattle, bison, buffalo, antelopes, sheep and goats. A member of this family is called a bovid. With 143 extant species and 300 known extinct species, the family Bovidae consists of 11 major subfamilies and thirteen major tribes. The family evolved 20 million years ago, in the early Miocene.
Australopithecus afarensis is an extinct species of australopithecine which lived from about 3.9–2.9 million years ago (mya) in the Pliocene of East Africa. The first fossils were discovered in the 1930s, but major fossil finds would not take place until the 1970s. From 1972 to 1977, the International Afar Research Expedition—led by anthropologists Maurice Taieb, Donald Johanson and Yves Coppens—unearthed several hundreds of hominin specimens in Hadar, Ethiopia, the most significant being the exceedingly well-preserved skeleton AL 288-1 ("Lucy") and the site AL 333. Beginning in 1974, Mary Leakey led an expedition into Laetoli, Tanzania, and notably recovered fossil trackways. In 1978, the species was first described, but this was followed by arguments for splitting the wealth of specimens into different species given the wide range of variation which had been attributed to sexual dimorphism. A. afarensis probably descended from A. anamensis and is hypothesised to have given rise to Homo, though the latter is debated.
Paraceratherium is an extinct genus of hornless rhinocerotoids belonging to the family Paraceratheriidae. It is one of the largest terrestrial mammals that has ever existed and lived from the early to late Oligocene epoch. The first fossils were discovered in what is now Pakistan, and remains have been found across Eurasia between China and the Balkans. Paraceratherium means "near the hornless beast", in reference to Aceratherium, the genus in which the type species P. bugtiense was originally placed.
Monogamous pairing in animals refers to the natural history of mating systems in which species pair bond to raise offspring. This is associated, usually implicitly, with sexual monogamy.
Nephila pilipes is a species of golden orb-web spider. It resides all over countries in East and Southeast Asia as well as Oceania. It is commonly found in primary and secondary forests and gardens. Females are large and grow to a body size of 30–50 mm, with males growing to 5–6 mm. It is the second largest of the orb-weaving spiders apart from the recently discovered Nephila komaci. The first, second, and fourth pairs of legs of juvenile females have dense hairy brushes, but these brushes disappear as the spider matures.
Iranotherium is an extinct genus of large elasmotheriine rhinocerotids, comparable in size to a modern white rhino. It is known from the Late Miocene (Tortonian) of Maragha, Iran and the middle part of the Liushu formation of northwestern China. It was a precursor to the related Sinotherium and may have been ultimately outcompeted by its descendant. This species is most well known for showing unique sexual dimorphism among rhinos.
Chilotherium is an extinct genus of rhinocerotids endemic to Eurasia during the Miocene through Pliocene living for 13.7—3.4 mya, existing for approximately 10.3 million years.
Sexual dimorphism describes the morphological, physiological, and behavioral differences between males and females of the same species. Most primates are sexually dimorphic for different biological characteristics, such as body size, canine tooth size, craniofacial structure, skeletal dimensions, pelage color and markings, and vocalization. However, such sex differences are primarily limited to the anthropoid primates; most of the strepsirrhine primates and tarsiers are monomorphic.
Gracile capuchin monkeys are capuchin monkeys in the genus Cebus. At one time all capuchin monkeys were included within the genus Cebus. In 2011, Jessica Lynch Alfaro et al. proposed splitting the genus between the robust capuchin monkeys, such as the tufted capuchin, and the gracile capuchins. The gracile capuchins retain the genus name Cebus, while the robust species have been transferred to Sapajus.
Onthophagus taurus, the taurus scarab, is a species of dung beetle in the genus Onthophagus and the family Scarabaeidae. Also known as the bull-headed dung beetle, it is a species that specializes in cattle dung and is widely utilized to maintain clean pastures, making it agriculturally valuable. These beetles are typically 8–10 millimetres (0.31–0.39 in) in size. The males of this species exhibit distinct characteristics: large “major” males possess long, sweeping, curved horns resembling those of a longhorn bull, while small “minor” males have tiny horns that project upward from the back of their heads. Females, on the other hand, lack horns. These small beetles are oval shaped, the color is usually black or reddish brown. Sometimes the pronotum has a weak metallic sheen.
Sexual selection in mammals is a process the study of which started with Charles Darwin's observations concerning sexual selection, including sexual selection in humans, and in other mammals, consisting of male–male competition and mate choice that mold the development of future phenotypes in a population for a given species.
Sexual selection in scaled reptiles studies how sexual selection manifests in snakes and lizards, which constitute the order Squamata of reptiles. Each of the over three thousand snakes use different tactics in acquiring mates. Ritual combat between males for the females they want to mate with includes topping, a behavior exhibited by most viperids in which one male will twist around the vertically elevated fore body of its opponent and forcing it downward. It is common for neck biting to occur while the snakes are entwined.
Sexual selection in amphibians involves sexual selection processes in amphibians, including frogs, salamanders and newts. Prolonged breeders, the majority of frog species, have breeding seasons at regular intervals where male-male competition occurs with males arriving at the waters edge first in large number and producing a wide range of vocalizations, with variations in depth of calls the speed of calls and other complex behaviours to attract mates. The fittest males will have the deepest croaks and the best territories, with females making their mate choices at least partly based on the males depth of croaking. This has led to sexual dimorphism, with females being larger than males in 90% of species, males in 10% and males fighting for groups of females.
Sexual dimorphism is the condition where sexes of the same species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. Sexual dimorphism in carnivorans, in which males are larger than females, is common. Sexual selection is frequently cited as the cause of the intraspecific divergence in body proportions and craniomandibular morphology between the sexes within the Carnivora order. It is anticipated that animals with polygynous mating systems and high levels of territoriality and solitary behavior will exhibit the highest levels of sexual size dimorphism. Pinnipeds offer an illustration for this.
