Message 1 of 2 (845748)
12-19-2018 5:10 PM
It's been a while ...
‘Little Foot’ skeleton analysis reignites debate over the hominid’s species
|FOSSIL PUZZLE Paleoanthropologist Ron Clarke excavates the skull of a hominid skeleton known as Little Foot. |
Controversial new investigations of the adult female conclude that she lived in southern Africa nearly 3.7 million
years ago and belonged to a species that many researchers don’t regard as valid.
A nearly complete hominid skeleton known as Little Foot has finally been largely freed from the stony shell in which it was discovered in a South African cave more than 20 years ago. And in the first formal analyses of the fossils, researchers say the 3.67-million-year-old Little Foot belonged to its own species.
In four papers posted online at bioRxiv.org between November 29 and December 5, paleoanthropologist Ronald Clarke of the University of the Witwatersrand in Johannesburg and colleagues assign Little Foot to a previously proposed species, Australopithecus prometheus, that has failed to gain traction among many researchers.
Many other researchers, however, regard Little Foot as an early member of a hominid species called Australopithecus africanus. Anthropologist Raymond Dart first identified A. africanus in 1924 from an ancient youngster’s skull called the Taung Child. Hundreds of A. africanus fossils have since been found in South African caves, including Sterkfontein. One of those caves, Makapansgat, produced a partial braincase that Dart assigned to A. prometheus in 1948. But Dart dropped that label after 1955, assigning the braincase and another Makapansgat fossil to A. africanus.
Based on their research, Clarke and colleagues say that Little Foot’s distinctive skeleton, an adult female that is at least 90 percent complete, justifies reviving the rejected species. “Little Foot fits comfortably in A. prometheus,” Clarke says.
In one new study, Clarke and Witwatersrand colleague Kathleen Kuman describe skull features that the duo says set Little Foot apart from A. africanus. For example, the researchers point to the vertical sides of Little Foot’s braincase relative to A. africanus’ sloping sides and to heavily worn teeth from the front of the mouth to the first molars. Such wear probably resulted from eating tubers, leaves and fruits with tough skins, Clarke says. A. africanus ate a greater variety of foods that took a lesser toll on teeth, he adds.
A second investigation, led by evolutionary biologist Robin Crompton of the University of Liverpool in England, finds that Little Foot had humanlike hips and limb proportions, with longer legs than arms, indicative of upright walking. Those features are most comparable to a 3.6-million-year-old Australopithecus afarensis skeleton from East Africa dubbed Big Man, suggesting that the ability to walk upright evolved at the same time in different regions (SN: 7/17/10, p. 5).
Independent studies of Little Foot’s body parts will help to resolve controversies about her evolutionary identity and way of life, predicts paleoanthropologist Carol Ward of the University of Missouri in Columbia. “This skeleton holds so much scientific potential.”
... since we head a lumper/splitter "controversy.
The controversy is over what species we call little-foot, not whether it is transitional along the path from early ape to human.
Australopithecus afarensis (Like Lucy)
A "Splitter generally prefers more groups while a "Lumpre" generally prefers fewer groups, and it all comes down to arbitrary distinctions of groups along the path from ape to modern human
And I also recall the discussion on New Species of Homo Discovered: Homo naledi of a "braided" history ... from the article:
This Face Changes the Human Story. But How?
Berger himself thinks the right metaphor for human evolution, instead of a tree branching from a single root, is a braided stream: a river that divides into channels, only to merge again downstream. Similarly, the various hominin types that inhabited the landscapes of Africa must at some point have diverged from a common ancestor. But then farther down the river of time they may have coalesced again, so that we, at the river’s mouth, carry in us today a bit of East Africa, a bit of South Africa, and a whole lot of history we have no notion of whatsoever. ...
Because Homo naledi is a mosaic of features some modern derived features and some preserved ancestral features, and that applies to other species, such that there is some mixing and matching going on, this suggests some hybridization in the past. We also know from DNA analysis that there was some hybridization with Homo neanderthalus (alt Homo sapiens neanderthalus )
Likewise we have the Denisovans
The Denisovans or Denisova hominins ( /dɪˈniːsəvə/ di-NEE-sə-və ) are an extinct species or subspecies of archaic humans in the genus Homo. Pending its status as either species or subspecies, it currently carries the temporary names Homo sapiens [subspecies] denisova, and Homo sp. Altai. In March 2010, scientists announced the discovery of an undated finger bone fragment of a juvenile female found in the Denisova Cave in the Altai Mountains in Siberia, a cave that has also been inhabited by Neanderthals and modern humans. The mitochondrial DNA (mtDNA) of the finger bone showed it to be genetically distinct from Neanderthals and modern humans. The nuclear genome from this specimen suggested that Denisovans shared a common origin with Neanderthals, that they ranged from Siberia to Southeast Asia, and that they lived among and interbred with the ancestors of some modern humans, with about 3% to 5% of the DNA of Melanesians and Aboriginal Australians and around 6% in Papuans deriving from Denisovans.
|The evolution and geographic spread of Denisovans as compared with other groups|
A 2013 comparison with the genome of another Neanderthal from the Denisova cave revealed local interbreeding with local Neanderthal DNA representing 17% of the Denisovan genome, and evidence of interbreeding with an as yet unidentified ancient human lineage. Analysis of DNA from two teeth found in layers different from the finger bone revealed an unexpected degree of mtDNA divergence among Denisovans. Two teeth belonging to different members of the Denisova cave population have been reported. In November 2015, a tooth fossil containing DNA was reported to have been found and studied.
Denisovans and Neanderthals split from Homo sapiens around 600,000 up to 744,000 years ago and diverged from each other about 200,000 years later.
Some cross-breeding is beneficial, Wikipedia defines Heterosis as:
Heterosis, hybrid vigor, or outbreeding enhancement, is the improved or increased function of any biological quality in a hybrid offspring. The adjective derived from heterosis is heterotic.
An offspring exhibits heterosis if its traits are enhanced as a result of mixing the genetic contributions of its parents. These effects can be due to Mendelian or non-Mendelian inheritance.
Heterosis is often discussed as the opposite of inbreeding depression although differences in these two concepts can be seen in evolutionary considerations such as the role of genetic variation or the effects of genetic drift in small populations on these concepts. Inbreeding depression occurs when related parents have children with traits that negatively influence their fitness largely due to homozygosity. In such instances, outcrossing should result in heterosis.
Not all outcrosses result in heterosis. For example, when a hybrid inherits traits from its parents that are not fully compatible, fitness can be reduced. This is a form of outbreeding depression.
So there can be inter-breeding of developing daughter species before full reproductive isolation is achieved, if it ever is. All extant Human varieties are capable of interbreeding, all extant varieties of Equines less so.
Personally I think "species" designations are fluid distinctions we use for identifying and discussing stages along the path of evolution. This is because the breeding population is where evolution occurs, and so all the stages all occur with a breeding population, ie - a species, you never see specification from within the breeding population, just the process of evolution, because that is how life survives and reproduces: it seems messy and complicated but it's actually quite simple.
Basically the final uncovering and documentation of little-foot skeleton (including the skull) fills in the blanks for this specimen, they are a welcome addition to the bank of fossils that fully support the evolution of humankind from early apes at about 3 to 4 million years ago.