| Homininae | |
|---|---|
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| Three hominines – an adulthuman male (Leonard Carmichael) holding a juvenilegorilla (left) and a juvenilechimpanzee (right). | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Primates |
| Family: | Hominidae |
| Subfamily: | Homininae Gray, 1825 |
| Type species | |
| Homo sapiens Linnaeus, 1758 | |
| Tribes | |
TheHomininae (/hɒmɪˈnaɪniː/;hominines) is asubfamily of the familyHominidae (hominids). The Homininae encompass humans, and are also called "African hominids" or "African apes".[1][2] This subfamily includes two tribes,Hominini andGorillini, both havingextant (or living) species as well asextinct species.
TribeHominini includes: the extant genusHomo, which comprises only one extant species — modernhuman (Homo sapiens), and numerous extinct human species; and the extant genusPan, which includes two extant species,chimpanzees andbonobos. TribeGorillini (gorillas) contains one extant genus,Gorilla, with two extant species, with variants, and one known extinct genus. Alternatively, the genusPan is considered by some to belong, instead of to a subtribePanina, to its own separate tribe, (so-called) "Panini," which would be a third tribe for Homininae.
Some classification schemes provide a more comprehensive account of extinct groups (see section "Taxonomic Classification" below). For example, tribe Hominini shows two subtribes: subtribeHominina, which contains at least two extinctgenera; and subtribe Panina, which presents only the extant genus,Pan (chimpanzees/bonobos), as fossils of extinct chimpanzees/bonobos are very rarely found.
The Homininae comprise allhominids that arose after the subfamilyPonginae (orangutans) split from the line of thegreat apes. The Homininaecladogram has three main branches leading to gorillas (via the tribe Gorillini), to humans, and to chimpanzees (via the tribe Hominini and subtribes Hominina and Panina, see graphic "Evolutionary tree" below). There are two living species each of Panina, chimpanzees and bonobos, and two living and one extinct species of gorillas. Traces of extinctHomo species, includingHomo floresiensis, have been found with dates as recent as 40,000 years ago. Individual members of this subfamily are calledhominine orhominines — not to be confused with the termshominins orHominini.[Note 1]
Until 1970, the family (and term) Hominidae meant humans only; the non-humangreat apes were assigned to the then-familyPongidae.[3] Later discoveries led to revised classifications, with the greatapes then united with humans (now in subfamily Homininae)[4] as members of family Hominidae[5] By 1990, it was recognized thatgorillas andchimpanzees are more closely related tohumans than they are toorangutans, leading to their (gorillas' and chimpanzees') placement in subfamily Homininae as well.[6]
The subfamily Homininae can be further subdivided into three branches, the tribeGorillini (gorillas), the tribeHominini with subtribesPanina (chimpanzees/bonobos) andHominina (humans and their extinct relatives), and the extinct tribeDryopithecini. TheLate Miocene fossilNakalipithecus nakayamai, described in 2007, is abasal member of thisclade, as is, perhaps, its contemporaryOuranopithecus; that is, they are not assignable to any of the three extant branches. Their existence suggests that the Homininae tribes diverged not earlier than about 8 million years ago (seeHuman evolutionary genetics).
Today, chimpanzees and gorillas live intropical forests with acid soils that rarely preserve fossils. Although no fossil gorillas have been reported, four chimpanzee teeth about 500,000 years old have been discovered in the East-African rift valley (Kapthurin Formation, Kenya), where many fossils from the human lineage (hominins)[Note 1] have been found.[7] This shows that some chimpanzees lived close toHomo (H. erectus orH. rhodesiensis) at the time; the same is likely true for gorillas.[4]
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| Hominoidea (Apes) | |
| Hominidae (Great apes) |
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Homininae
The age of the subfamily Homininae (of theHomininae–Ponginae last common ancestor) is estimated at some 14[9] to 12.5 million years (Sivapithecus).[10][11] Its separation into Gorillini and Hominini (the "gorilla–human last common ancestor", GHLCA) is estimated to have occurred at about8 to 10 million years ago (TGHLCA) during the lateMiocene, close to the age ofNakalipithecus nakayamai.[12]
There is evidence there was interbreeding of Gorillas and the Pan–Homo ancestors until right up to the Pan–Homo split.[13]
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Recent studies ofArdipithecus ramidus (4.4 million years old) andOrrorin tugenensis (6 million years old) suggest some degree of bipedalism.Australopithecus and earlyParanthropus may have beenbipedal. Very early hominins such asArdipithecus ramidus may have possessed an arboreal type of bipedalism.[14]
The evolution ofbipedalism encouraged multiple changes among hominins especially when it came tobipedalism in humans as they were now able to do many other things as they began to walk with their feet. These changes included the ability to now use their hands to create tools or carry things with their hands, the ability to travel longer distances at a faster speed, and the ability to hunt for food. According to researchers, humans were able to be bipedalists due to Darwin's Principle ofnatural selection. Darwin himself believed that larger brains in humans made an upright gait necessary, but had no hypothesis for how the mechanism evolved.
The first major theory attempting to directly explanation the origins ofbipedalism was theSavannah hypothesis (Dart 1925.) This theory hypothesized that hominins became bipedalists due to the environment of the Savanna such as the tall grass and dry climate. This was later proven to be incorrect due to fossil records that showed that hominins were still climbing trees during this era.
AnthropologistOwen Lovejoy has suggested thatbipedalism was a result ofsexual dimorphism in efforts to help with the collecting of food. In his Male Provisioning Hypothesis introduced in 1981, lowered birth rates in early hominids increased pressure on males to provide for females and offspring. While females groomed and cared for their children with the family group, males ranged to seek food and returned bipadally with full arms. Males who could better provide for females in this model were more likely to mate and produce offspring.[15]
Anthropologist Yohannes Haile-Selassie, an expert onAustralopithecus anamensis, discusses the evidence that Australopithecus were one of the first hominins to evolve into obligate bipedalists. The remains of this subfamily are very important in the field of research as it presents possible information regarding how these primates adapted from tree life to terrestrial life. This was a huge adaptation as it encouraged many evolutionary changes within hominins including the ability to use their hand to make tools and gather food, as well as a larger brain development due to their change in diet.[16]
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There has been a gradual increase in brain volume (brain size) as the ancestors of modern humans progressed along thetimeline of human evolution, starting from about 600 cm3 inHomo habilis up to 1500 cm3 inHomo neanderthalensis. However, modernHomo sapiens have a brain volume slightly smaller (1250 cm3) than Neanderthals, women have a brain slightly smaller than men and the Flores hominids (Homo floresiensis), nicknamed hobbits, had a cranial capacity of about 380 cm3 (considered small for a chimpanzee), about a third of theHomo erectus average. It is proposed that they evolved fromH. erectus as a case of insular dwarfism.[citation needed] In spite of their smaller brain, there is evidence thatH. floresiensis used fire and made stone tools at least as sophisticated as those of their proposed ancestorsH. erectus.[17] In this case, it seems that for intelligence, the structure of the brain is more important than its size.[18]
The current size of the human brain is a big distinguishing factor that separates humans from other primates. Recent examination of the human brain shows that the brain of a human is about more than four times the size ofgreat apes and 20 times larger than the brain size ofold world monkeys. A study[19] was conducted to help determine the evolution of the brain size within the sub family Homininae that tested the genes ASPM (abnormal spindle-like microcephaly associated) and MCHP1(microcephalin-1) and their association with the human brain. In this study researchers discovered that the increase in brain size is correlated to the increase of both ASP and MCPH1. MCPH1 is very polymorphic in humans compared togibbons,Old World monkeys. This gene helps encouragegrowth of the brain. Further research indicated that the MCPH1 gene in humans could have also been an encouraging factor of population expansion. Other researchers have included that the diet was an encouraging factor to brain size as protein intake increased this helped brain development.[19]
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Sexuality is related to family structure and partly shapes it. The involvement of fathers in education is quite unique to humans, at least when compared to other Homininae.Concealed ovulation andmenopause in females also occur in a few other primates, but are uncommon in other species.Testis andpenis size seem to be related to family structure:monogamy orpromiscuity, orharem, in humans, chimpanzees or gorillas, respectively.[20][21] The levels ofsexual dimorphism are generally seen as a marker ofsexual selection. Studies have suggested that the earliest hominins were dimorphic and that this lessened over the course of the evolution of the genusHomo, correlating with humans becoming more monogamous, whereas gorillas, who live in harems, show a large degree of sexual dimorphism. Concealed (or "hidden") ovulation means that the phase of fertility is not detectable in women, whereas chimpanzees advertise ovulation via an obvious swelling of the genitals. Females can be partly aware of their ovulation along with their menstrual phases, but men are essentially unable to detect ovulation in women. Most primates have semi-concealed ovulation. Thus, one can think that the common ancestor had semi-concealed ovulation, which was inherited by gorillas, and that later evolved in concealed ovulation in humans and advertised ovulation in chimpanzees. Menopause also occurs inrhesus monkeys, and possibly in chimpanzees, but does not in gorillas and is quite uncommon in other primates (and other mammal groups).[21]
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