Difference between revisions of "Hominin" - New World Encyclopedia

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{{Taxobox | color = pink
 
{{Taxobox | color = pink
 
| name = Hominini
 
| name = Hominini
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| subfamilia = [[Homininae]]
 
| subfamilia = [[Homininae]]
 
| tribus = '''Hominini'''
 
| tribus = '''Hominini'''
| tribus_authority = [[John Edward Gray|Gray]], [[1825]]
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| tribus_authority = [[John Edward Gray|Gray]], 1825
 
| subdivision_ranks = [[Genus|Genera]]
 
| subdivision_ranks = [[Genus|Genera]]
 
| subdivision =  
 
| subdivision =  
 
Subtribe [[Panina (subtribe)|Panina]]
 
Subtribe [[Panina (subtribe)|Panina]]
*''[[Chimpanzee|Pan]]'' ([[chimpanzee]]s)
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*''[[Chimpanzee|Pan]]'' (chimpanzees)
 
Subtribe [[Hominina]]  
 
Subtribe [[Hominina]]  
 
*''[[Homo (genus)|Homo]]'' ([[human]]s)
 
*''[[Homo (genus)|Homo]]'' ([[human]]s)
*†''[[Paranthropus]]''
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*†''[[Australopithecus|Paranthropus]]''
 
*†''[[Australopithecus]]''
 
*†''[[Australopithecus]]''
 
*†''[[Sahelanthropus]]''
 
*†''[[Sahelanthropus]]''
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{{dablink|For an explanation of very similar terms see ''[[Hominid]]''.}}
 
{{dablink|For an explanation of very similar terms see ''[[Hominid]]''.}}
  
'''Hominin''' is a member of the tribe '''Hominini''', primate group that only includes [[human]] ([[Homo (genus)|genus ''Homo''), [[chimpanzee]]s (''Pan''), and their [[extinct]] ancestors.  
+
A '''Hominin''' is any member of the [[primate]] tribe '''Hominini,''' a [[taxonomy|classification]] that generally is considered to include only [[human]]s ([[Homo (genus)|genus ''Homo'']]), [[chimpanzee]]s (''Pan''), and their [[extinct]] ancestors. In recent classifications, Hominini is a tribe of the subfamily Homininae (humans, chimpanzees, [[gorilla]]s) of the family Hominidae (humans, chimpanzees, gorillas, and [[orangutan]]s).
  
The creation of this taxon is the result of the current idea that the least similar species of a [[trichotomy]] should be separated from the other two. Through [[DNA]] comparison, scientists believe they have determined that the ''Pan/Homo'' split happened about 5 to 7 million years ago.<ref name=split> {{cite web | url = http://www.physorg.com/news9211.html | title =  Scientists narrow time limits for human, chimp split | accessdate = 2005-12-21 | data = 2005-12-20 | work = [http://www.physorg.com PhysOrg.com]}}</ref> It is interesting to note that no fossil species on the ''Pan'' side of the split have been determined; all of the extinct genera listed to the right are ancestral to ''Homo'', or are offshoots of such. However, both ''[[Orrorin]]'' and ''[[Sahelanthropus]]'' existed around the time of the split, and so may be ancestral to both humans and chimpanzees.
+
Chimpanzees and humans are placed together in Hominini because of their remarkable anatomical and biochemical similarities and because research suggests chimpanzees are ''Homo's'' closest living relatives. Indeed, chimpanzees and humans share over 98 percent genetic similarity (see [[Chimpanzee#chimpanzees and humans|chimpanzee]] article).
 +
 
 +
However, in addition to numerous physical differences&mdash;chimpanzees rarely have heart attacks, are resistant to [[malaria]] caused by ''Plasmodium falciparum,'' and do not go through menopause (Wood 2006), for example&mdash;it should be noted that humans define themselves not only according to morphology and DNA structure, but also in terms of culture, psychology, intelligence, behavior, religion, and other aspects. In such ways, there is a striking gap between humans and chimpanzees. (See [[chimpanzee#Chimpanzees and humans|Chimpanzees and humans]], [[Hominidae]], and ''[[Homo sapiens]]'' for uniqueness of humans.)
 +
 
 +
==Overview of Hominini classification==
 +
 
 +
Primate classification has undergone many revisions over the years, from the 1960s when humans were the only extant species in the family Hominidae, until today, when it is common to place [[chimpanzee]]s, [[gorilla]]s, and [[orangutan]]s in Hominidae as well. There are even other taxonomic schemes, such as placing extant and extinct chimpanzees and gorillas in the family Panidae, orangutans in the historical group Pongidae, and humans in Hominidae.
 +
 
 +
The creation of the taxon Hominini is the result of the current idea that the least similar species of a trichotomy should be separated from the other two. Thus, orangutans are separated into the subfamily Ponginae while the other great apes are placed in subfamily Homininae. By various methods ([[protein]] differences, [[DNA]] differences, etc.), it is determined that the branching point between humans and chimpanzees is more recent than between chimpanzees and gorillas, thus suggesting that chimpanzees are the closest extant relatives of ''Homo.'' (Mayr 2001)). The gorillas are separated into tribe Gorillini, while extant and extinct humans and chimpanzees are placed in tribe Hominini.  
  
In the proposal of Mann and Weiss (1996),<ref name=Mann>{{cite journal | author = Mann, Alan and Mark Weiss | year = 1996 | title = Hominoid Phylogeny and Taxonomy: a consideration of the molecular and Fossil Evidence in an Historical Perspective | journal = Molecular Phylogenetics and Evolution | volume = 5 | issue = 1 | pages = 169-181}}</ref> the tribe ''Hominini'' includes ''Pan'' as well as ''Homo'' as separate subtribes. ''Homo'' (and, by inference, all bipedal apes) is by itself only in the subtribe [[Hominina]], while ''Pan'' is in the [[Panina (subtribe)|Panina]] subtribe.
 
 
[[Image:Hominini.PNG|left|frame|[[Extant]] Hominoid family tree]]
 
[[Image:Hominini.PNG|left|frame|[[Extant]] Hominoid family tree]]
 +
The anatomical and biochemical similarity between chimpanzees and humans is indeed striking. Various studies show that they have about 98 to 99.4 percent of their [[DNA]] in common (Wildman et al. 2003, Wood 2006). For example, comparisons between chimpanzees and humans in terms of [[protein]] sequences, [[allele]] differences, and DNA heteroduplex melting points show more than 98 percent identity (King and Wilson 1975; Wood 2006). Ebersberger et al. (2002) found a difference of only 1.24 percent when he aligned 1.9 million [[nucleotide]]s of chimpanzee DNA and compared them with the corresponding human sequences in the human genome (Wood 2006). Using a 4.97 million nucleotide portion of DNA from human chromosome 7 and comparing to chimpanzee orthologies yielded only 1.13 percent mismatches (Liu et al. 2003). Other biochemical comparisons can be seen in the article on [[chimpanzee#chimpanzees and humans|chimpanzees]].
  
The exact criteria for membership in the Homininae are not clear, but the subfamily generally includes those [[species]] which share more than 97% of their [[DNA]] with the modern human [[genome]], and exhibit a capacity for [[language]] or for simple [[culture]]s beyond the family or band. The [[theory of mind]] including such faculties as mental state attribution, empathy and even empathetic deception is a controversial criterion distinguishing the adult human alone among the hominids. Humans acquire this capacity at about four and a half years of age, whereas it has neither been proven nor disproven that gorillas and chimpanzees develop a theory of mind.<ref>{{cite journal | author = Heyes, C. M. | year = 1998 | title = THEORY OF MIND IN NONHUMAN PRIMATES | journal = Behavioral and Brain Sciences | id = bbs00000546 | url = http://www.bbsonline.org/documents/a/00/00/05/46/index.html}}</ref> This is also the case for some [[new world monkey]]s outside the family of great apes, as, for example, the [[Capuchin_monkey#Theory_of_mind|capuchin monkeys]].
+
In the 1996 proposal of Mann and Weiss, the tribe Hominini included the separate subtribes of Panina and Hominina. The genus [[Homo (genus)|Homo]], and, by inference, all bipedal apes, is by itself only in the subtribe Hominina, while ''Pan'' is in the Panina subtribe.  
  
However, without the ability to test whether early members of the Homininae (such as ''[[Homo erectus]]'', ''[[Homo neanderthalensis]]'', or even the australopithecines) had a theory of mind, it is difficult to ignore similarities seen in their living cousins. Despite an apparent lack of real culture and significant physiological and psychological differences, some say that the orangutan may also satisfy these criteria. These scientific debates take on political significance for advocates of [[Great Ape personhood]].
+
Chimpanzees are so similar to humans that some scientists have proposed that the two chimpanzee species, ''troglodytes'' and ''paniscus,'' belong with ''sapiens'' in the genus ''[[Homo (genus)|Homo]],'' rather than in ''Pan.'' Of course, this again considers only anatomical and genetic differences, rather than a comprehensive view that includes social, psychological, religious, and other factors.
  
In [[2002]], a 6&ndash;7 million year old [[fossil]] [[skull]] nicknamed "Toumaï" by its discoverers, and formally classified as ''[[Sahelanthropus tchadensis]]'', was discovered in [[Chad]] and is possibly the earliest hominid [[fossil]] ever found. In addition to its age, Toumaï, unlike the 3&ndash;4 million year younger [[gracile australopithecine]] dubbed "[[Australopithecus afarensis|Lucy]]", has a relatively flat face without the prominent snout seen on other pre-''[[Homo (genus)|Homo]]'' hominids. Some researchers have made the suggestion that this previously unknown species may in fact be a direct ancestor of modern humans (or at least closely related to a direct ancestor). Others contend that one fossil is not enough to make such a claim because it would overturn the conclusions of over 100 years of [[anthropology|anthropological]] study. A report on this finding was published in the journal ''[[Nature (journal)|Nature]]'' on [[July 11]], [[2002]]. While some scientists claim that it is merely the skull of a female gorilla, others have called it the most important hominin fossil since ''Australopithecus''.
+
==Pan/Homo split==
  
In addition to the Tourmai fossil, some experts use evidence from the genome to argue that the species associated with the chimpanzees and proto-humans split interbred over a long period of time, swapping genes, before making a final separation. A paper, whose authors include [[David Reich]] and [[Eric Lander]] (Harvard and the Massachusetts Institute of Technology (MIT)), was published in journal ''[[Nature (journal)|Nature]]'' in May 2006.
+
Through a study of [[protein]]s, comparison of [[DNA]], and use of a molecular clock (a method of calculating evolution based on the speed at which [[gene]]s mutate), scientists believe the''Pan/Homo'' split happened about 5 to 8 million years ago (Mayr 2001, Physorg 2005). One study, utilizing 167 nuclear protein-coding genes, showed the split to be roughly 5 to 7 million years ago (Kumar et al. 2005), while another analysis, utilizing 20 million aligned base pairs, revealed that human–chimpanzee [[speciation]] occurred less than 6.3 million years ago and probably more recently, such as 5.4 mya (Patterson et al. 2006). This later study compared key sequences of genes rather than looking at average genetic differences between human and chimp. Interestingly, this later study claims that study of chromosome X shows features that could best be explained if the chimpanzee and human lineages initially diverged, but then later exchanged genes before final separation.  
  
It is generally believed that the ''Pan/Homo'' split occurred about 6.5–7.4 million years ago, but the [[molecular clock]] (a method of calculating evolution based on the speed at which genes mutate) suggests the genera split 5.4–6.3 million years ago. Previous studies looked at average genetic differences between human and chimp. The new study compares the ages of key sequences of genes of modern humans and modern chimps. Some sequences are younger than others, indicating that chimps and humans gradually split apart over a period of 4 million years. The youngest human chromosome is the X sex chromosome which is about 1.2 million years more recent than the 22 autosomes. The X chromosome is known to be vulnerable to selective pressure. Its age suggests there was an initial split between the two species, followed by gradual divergence and interbreeding that resulted in younger genes, and then a final separation.
+
Kumar et al. (2005) note that hypotheses "about the timing of human-chimpanzee divergence demand more precise [[fossil]]-based calibrations." However, it is interesting to note that no fossil species on the ''Pan'' side of the split have been determined; all of the extinct genera are ancestral to ''Homo,'' or are offshoots of such. Mayr (2001), for example, notes that no [[hominid]] fossils (in the narrow sense of the word as including humans and their relatives) nor fossil chimpanzees have been found between 6 and 13 million years ago. However, both ''[[Orrorin]]'' and ''[[Sahelanthropus]]'' existed around the time of the split, and so may be ancestral to both humans and chimpanzees.
 +
 
 +
In 2002, a 6&ndash;7 million year old [[fossil]] skull nicknamed "Toumaï" by its discoverers, and formally classified as ''[[Sahelanthropus tchadensis]],'' was discovered in [[Chad]] and is possibly the earliest hominid fossil ever found. In addition to its age, Toumaï, unlike the 3&ndash;4 million year younger gracile [[australopithecine]] dubbed "[[Australopithecus afarensis|Lucy]]," has a relatively flat face without the prominent snout seen on other pre-''[[Homo (genus)|Homo]]'' hominids. Some researchers have made the suggestion that this previously unknown species may in fact be a direct ancestor of modern humans (or at least closely related to a direct ancestor). Others contend that one fossil is not enough to make such a claim because it would overturn the conclusions of over 100 years of [[anthropology|anthropological]] study. While some scientists claim that it is merely the skull of a female gorilla, others have called it the most important hominin fossil since ''Australopithecus.''
  
  
==See also==
 
*[[Cladistics]]
 
*[[Human evolution]]
 
<br clear="all" />
 
  
 
==References==
 
==References==
{{references-small}}
 
  
{{Human Evolution}}
+
* Ebersberger, I., D. Metzler, C. Schwarz, and S. Paabo. 2002. Genomewide comparison of DNA sequences between humans and chimpanzees. ''American Journal of Human Genetics'' 70:1490–97.
[[Category:apes]]
+
* King, M.C. and A.C. Wilson. 1975. Evolution at two levels in Humans and Chimpanzees. ''Science'' 188: 107-116
[[Category:Life sciences]]
+
* Kumar, S., A. Filipski, V. Swarna, A. Walker, and S. B. Hedges. 2005. Placing confidence limits on the molecular age of the human-chimpanzee divergence. ''PNAS'' December 19, 2005. Retrieved March 8, 2007.
 +
* Liu, G., NISC Comparative Sequencing Program, S. Zhao, J. A. Bailey, S. C. Sahinalp, C. Alkan, E. Tuzun, E. D. Green, and E. E. Eichler. 2003. Analysis of primate genomic variation reveals a repeat-driven expansion of the human genome. ''Genome Research'' 13:358–68.
 +
* Mann, A., and M. Weiss. 1996. Hominoid phylogeny and taxonomy: A consideration of the molecular and fossil evidence in an historical perspective. ''Molecular Phylogenetics and Evolution'' 5(1): 169-181.
 +
* Mayr, E. 2001. ''What Evolution Is.'' New York: Basic Books. ISBN 0465044255
 +
* Patterson, N., D. J. Richter, S. Gnerre, E. S. Lander, and D. Reich. 2006. Genetic evidence for complex speciation of humans and chimpanzees. ''Nature'' 441: 1103-1108.
 +
* Physorg. 2005. [http://www.physorg.com/news9211.html Scientists narrow time limits for human, chimp split.] ''Physorg.com.'' Retrieved December 21, 2005.
 +
* Wildman, D. E., M. Uddin, G. Liu, L. I. Grossman, and M. Goodman. 2003. Implications of natural selection in shaping 99.4% nonsynonymous DNA identity between humans and chimpanzees: Enlarging genus Homo. ''Proceedings of the National Academy of Sciences'' 100:7181–88.
 +
* Wood, T. C. 2006. [http://www.bryancore.org/bsg/opbsg/007.pdf The chimpanzee genome and the problem of biological similarity]. ''Occassional Papers of the BSG'' 7:1–18.
 +
 
 +
[[Category: Life sciences]]
 +
[[Category:Animals]]
 +
[[Category:Mammals]]
 +
[[Category:Primates]]
 +
[[Category:Human evolution]]
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{{credit|110396528}}
 
{{credit|110396528}}

Latest revision as of 08:52, 2 April 2008

Hominini
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Primates
Superfamily: Hominoidea
Family: Hominidae
Subfamily: Homininae
Tribe: Hominini
Gray, 1825
Genera

Subtribe Panina

  • Pan (chimpanzees)

Subtribe Hominina

A Hominin is any member of the primate tribe Hominini, a classification that generally is considered to include only humans (genus Homo), chimpanzees (Pan), and their extinct ancestors. In recent classifications, Hominini is a tribe of the subfamily Homininae (humans, chimpanzees, gorillas) of the family Hominidae (humans, chimpanzees, gorillas, and orangutans).

Chimpanzees and humans are placed together in Hominini because of their remarkable anatomical and biochemical similarities and because research suggests chimpanzees are Homo's closest living relatives. Indeed, chimpanzees and humans share over 98 percent genetic similarity (see chimpanzee article).

However, in addition to numerous physical differences—chimpanzees rarely have heart attacks, are resistant to malaria caused by Plasmodium falciparum, and do not go through menopause (Wood 2006), for example—it should be noted that humans define themselves not only according to morphology and DNA structure, but also in terms of culture, psychology, intelligence, behavior, religion, and other aspects. In such ways, there is a striking gap between humans and chimpanzees. (See Chimpanzees and humans, Hominidae, and Homo sapiens for uniqueness of humans.)

Overview of Hominini classification

Primate classification has undergone many revisions over the years, from the 1960s when humans were the only extant species in the family Hominidae, until today, when it is common to place chimpanzees, gorillas, and orangutans in Hominidae as well. There are even other taxonomic schemes, such as placing extant and extinct chimpanzees and gorillas in the family Panidae, orangutans in the historical group Pongidae, and humans in Hominidae.

The creation of the taxon Hominini is the result of the current idea that the least similar species of a trichotomy should be separated from the other two. Thus, orangutans are separated into the subfamily Ponginae while the other great apes are placed in subfamily Homininae. By various methods (protein differences, DNA differences, etc.), it is determined that the branching point between humans and chimpanzees is more recent than between chimpanzees and gorillas, thus suggesting that chimpanzees are the closest extant relatives of Homo. (Mayr 2001)). The gorillas are separated into tribe Gorillini, while extant and extinct humans and chimpanzees are placed in tribe Hominini.

Extant Hominoid family tree

The anatomical and biochemical similarity between chimpanzees and humans is indeed striking. Various studies show that they have about 98 to 99.4 percent of their DNA in common (Wildman et al. 2003, Wood 2006). For example, comparisons between chimpanzees and humans in terms of protein sequences, allele differences, and DNA heteroduplex melting points show more than 98 percent identity (King and Wilson 1975; Wood 2006). Ebersberger et al. (2002) found a difference of only 1.24 percent when he aligned 1.9 million nucleotides of chimpanzee DNA and compared them with the corresponding human sequences in the human genome (Wood 2006). Using a 4.97 million nucleotide portion of DNA from human chromosome 7 and comparing to chimpanzee orthologies yielded only 1.13 percent mismatches (Liu et al. 2003). Other biochemical comparisons can be seen in the article on chimpanzees.

In the 1996 proposal of Mann and Weiss, the tribe Hominini included the separate subtribes of Panina and Hominina. The genus Homo, and, by inference, all bipedal apes, is by itself only in the subtribe Hominina, while Pan is in the Panina subtribe.

Chimpanzees are so similar to humans that some scientists have proposed that the two chimpanzee species, troglodytes and paniscus, belong with sapiens in the genus Homo, rather than in Pan. Of course, this again considers only anatomical and genetic differences, rather than a comprehensive view that includes social, psychological, religious, and other factors.

Pan/Homo split

Through a study of proteins, comparison of DNA, and use of a molecular clock (a method of calculating evolution based on the speed at which genes mutate), scientists believe thePan/Homo split happened about 5 to 8 million years ago (Mayr 2001, Physorg 2005). One study, utilizing 167 nuclear protein-coding genes, showed the split to be roughly 5 to 7 million years ago (Kumar et al. 2005), while another analysis, utilizing 20 million aligned base pairs, revealed that human–chimpanzee speciation occurred less than 6.3 million years ago and probably more recently, such as 5.4 mya (Patterson et al. 2006). This later study compared key sequences of genes rather than looking at average genetic differences between human and chimp. Interestingly, this later study claims that study of chromosome X shows features that could best be explained if the chimpanzee and human lineages initially diverged, but then later exchanged genes before final separation.

Kumar et al. (2005) note that hypotheses "about the timing of human-chimpanzee divergence demand more precise fossil-based calibrations." However, it is interesting to note that no fossil species on the Pan side of the split have been determined; all of the extinct genera are ancestral to Homo, or are offshoots of such. Mayr (2001), for example, notes that no hominid fossils (in the narrow sense of the word as including humans and their relatives) nor fossil chimpanzees have been found between 6 and 13 million years ago. However, both Orrorin and Sahelanthropus existed around the time of the split, and so may be ancestral to both humans and chimpanzees.

In 2002, a 6–7 million year old fossil skull nicknamed "Toumaï" by its discoverers, and formally classified as Sahelanthropus tchadensis, was discovered in Chad and is possibly the earliest hominid fossil ever found. In addition to its age, Toumaï, unlike the 3–4 million year younger gracile australopithecine dubbed "Lucy," has a relatively flat face without the prominent snout seen on other pre-Homo hominids. Some researchers have made the suggestion that this previously unknown species may in fact be a direct ancestor of modern humans (or at least closely related to a direct ancestor). Others contend that one fossil is not enough to make such a claim because it would overturn the conclusions of over 100 years of anthropological study. While some scientists claim that it is merely the skull of a female gorilla, others have called it the most important hominin fossil since Australopithecus.


References
ISBN links support NWE through referral fees

  • Ebersberger, I., D. Metzler, C. Schwarz, and S. Paabo. 2002. Genomewide comparison of DNA sequences between humans and chimpanzees. American Journal of Human Genetics 70:1490–97.
  • King, M.C. and A.C. Wilson. 1975. Evolution at two levels in Humans and Chimpanzees. Science 188: 107-116
  • Kumar, S., A. Filipski, V. Swarna, A. Walker, and S. B. Hedges. 2005. Placing confidence limits on the molecular age of the human-chimpanzee divergence. PNAS December 19, 2005. Retrieved March 8, 2007.
  • Liu, G., NISC Comparative Sequencing Program, S. Zhao, J. A. Bailey, S. C. Sahinalp, C. Alkan, E. Tuzun, E. D. Green, and E. E. Eichler. 2003. Analysis of primate genomic variation reveals a repeat-driven expansion of the human genome. Genome Research 13:358–68.
  • Mann, A., and M. Weiss. 1996. Hominoid phylogeny and taxonomy: A consideration of the molecular and fossil evidence in an historical perspective. Molecular Phylogenetics and Evolution 5(1): 169-181.
  • Mayr, E. 2001. What Evolution Is. New York: Basic Books. ISBN 0465044255
  • Patterson, N., D. J. Richter, S. Gnerre, E. S. Lander, and D. Reich. 2006. Genetic evidence for complex speciation of humans and chimpanzees. Nature 441: 1103-1108.
  • Physorg. 2005. Scientists narrow time limits for human, chimp split. Physorg.com. Retrieved December 21, 2005.
  • Wildman, D. E., M. Uddin, G. Liu, L. I. Grossman, and M. Goodman. 2003. Implications of natural selection in shaping 99.4% nonsynonymous DNA identity between humans and chimpanzees: Enlarging genus Homo. Proceedings of the National Academy of Sciences 100:7181–88.
  • Wood, T. C. 2006. The chimpanzee genome and the problem of biological similarity. Occassional Papers of the BSG 7:1–18.

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