Early hominins—particularly the australopithecines, whose brains and anatomy are in many ways more similar to ancestral non-human apes—are less often referred to as "human" than hominins of the genus Homo. Some of the latter used fire, occupied much of Eurasia, and gave rise to anatomically modern Homo sapiens in Africa about 200,000 years ago. They began to exhibit evidence of behavioral modernity around 50,000 years ago, and migrated in successive waves to occupy all but the smallest, driest, and coldest lands. In the last 100 years, this has extended to permanently manned bases in Antarctica, offshore platforms, orbiting the Earth and landing on the Moon.
Publication Information
- Title : People of Earth / Human
- Scientific Classification :
- Kingdom : Animalia
- Phylum : Chordata
- Class : Mammalia
- Order : Primates
- Suborder : Haplorhini
- Family : Hominidae
- Genus : Homo
- Species : H. sapiens
- Binomial Name :
- Homo sapiens
- Linnaeus, 1758
- Subspecies :
- †Homo sapiens idaltu White et al., 2003
- Homo sapiens sapiens
Etymology and Definition
In common usage, the word "human" generally refers to the only extant species of the genus Homo — anatomically and behaviorally modern Homo sapiens. Its usage often designates differences between that species as a whole and any other group or entity. In scientific terms, the meanings of "hominid" and "hominin" have changed during the recent decades with advances in the discovery and study of the fossil ancestors of modern humans. The previously clear boundary between humans and apes has blurred, resulting in now acknowledging the hominids as encompassing multiple species, and Homo and close relatives since the split from chimpanzees as the only hominins. There is also a distinction between anatomically modern humans and Archaic Homo sapiens, the earliest fossil members of the species.
The species binomial Homo sapiens was coined by Carl Linnaeus in his 18th century work Systema Naturae. The generic name Homo is a learned 18th century derivation from Latin homō "man", ultimately "earthly being" (Old Latin hemō, a cognate to Old English guma "man", from PIE dʰǵʰemon-, meaning "earth" or "ground"). The species-name sapiens means "wise" or "sapient". Note that the Latin word homo refers to humans of either gender, and that sapiens is the singular form (while there is no such word as sapien).
History
Evolution and range
The genus Homo evolved and diverged from other hominins in Africa, after the human clade split from the chimpanzee lineage of the hominids (great apes) branch of the primates. Modern humans, defined as the species Homo sapiens or specifically to the single extant subspecies Homo sapiens sapiens, proceeded to colonize all the continents and larger islands, arriving in Eurasia 125,000–60,000 years ago,[19][20] Australia around 40,000 years ago, the Americas around 15,000 years ago, and remote islands such as Hawaii, Easter Island, Madagascar, and New Zealand between the years 300 and 1280
Evidence from molecular biology
The closest living relatives of humans are chimpanzees (genus Pan) and gorillas (genus Gorilla). With the sequencing of both the human and chimpanzee genome, current estimates of similarity between human and chimpanzee DNA sequences range between 95% and 99%. By using the technique called a molecular clock which estimates the time required for the number of divergent mutations to accumulate between two lineages, the approximate date for the split between lineages can be calculated. The gibbons (Hylobatidae) and orangutans (genus Pongo) were the first groups to split from the line leading to the humans, then gorillas (genus Gorilla) followed by the chimpanzees (genus Pan). The splitting date between human and chimpanzee lineages is placed around 4–8 million years ago during the late Miocene epoch. During this split, chromosome 2 was formed from two other chromosomes, leaving humans with only 23 pairs of chromosomes, compared to 24 for the other apes.
Evidence from the fossil record
There is little fossil evidence for the divergence of the gorilla, chimpanzee and hominin lineages. The earliest fossils that have been proposed as members of the hominin lineage are Sahelanthropus tchadensis dating from 7 million years ago, Orrorin tugenensis dating from 5.7 million years ago, and Ardipithecus kadabba dating to 5.6 million years ago. Each of these species has been argued to be a bipedal ancestor of later hominins, but all such claims are contested. It is also possible that any one of the three is an ancestor of another branch of African apes, or is an ancestor shared between hominins and other African Hominoidea (apes). The question of the relation between these early fossil species and the hominin lineage is still to be resolved. From these early species the australopithecines arose around 4 million years ago diverged into robust (also called Paranthropus) and gracile branches, possibly one of which (such as A. garhi, dating to 2.5 million years ago) is a direct ancestor of the genus Homo.
Anatomical adaptations
Human evolution is characterized by a number of morphological, developmental, physiological, and behavioral changes that have taken place since the split between the last common ancestor of humans and chimpanzees. The most significant of these adaptations are 1. bipedalism, 2. increased brain size, 3. lengthened ontogeny (gestation and infancy), 4. decreased sexual dimorphism. The relationship between all these changes is the subject of ongoing debate. Other significant morphological changes included the evolution of a power and precision grip, a change first occurring in H. erectus.
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