I have a couple of things to air out and Wikipedia is the quickest source once again.There is discussion about the practical definition of species under the headings for "Species"
http://en.wikipedia.org/wiki/Species
and especially the subsection, "Definition of Species", and then on the redirect section on "Species Problem"
http://en.wikipedia.org/wiki/Species_problem
For the most part I am one of the adherants of the point of view that the definition of species should be measured by a fixed unit of genetic distance, as much as possible. My working definition is that a million years' worth of evolutionary divergence equals a clear distinction between species. Most workers are vague about the distinction between species and subspecies: I personally regard subspecies as an arbitrary unit, which is useful to field ecologists but not of any value as a taxonomic grade. That part is not important in this discussion.
The Wikipedia article has a chart of species, which are estimated to be still awaiting discovery. That chart is attached in this article and the discovery of new animal species is exactly what cryptozoology is all about. Something like 61,000 species of vertebrates are awaiting discovery by the chart, which would include quite a few large land and s
ea mammals, on the usual flat cross-section percentage. The number of mammal species alone could number in the tens of thousands, and the number of LARGE mammal species yet to be discovered in the thousands, and still be only a very small cut out of that estimated figure.
Now my own expertise is in physical anthropology and to be precise, the measurement and comparison of fossil hominin skulls. I have several times made the statement that even if most wildmen reported are relic hominids, they could still be members of the same species as us. Here is a section out of the Wikipedia article on Homo heidelburgensis:
http://en.wikipedia.org/wiki/Homo_heidelbergensis
Divergent evolution
Most experts now agree that H. heidelbergensis is the direct ancestor of H. sapiens (with some uncertainty about such specimens as H. antecessor, now largely considered H. heidelbergensis) and H. neanderthalensis. Because of the radiation of H. heidelbergensis out of Africa and into Europe, the two populations were mostly isolated during the Wolstonian Stage and Ipswichian Stage, the last of the prolonged Quaternary glacial periods. Neanderthals diverged from H. heidelbergensis probably some 300,000 years ago in Europe, during the Wolstonian Stage; H. sapiens probably diverged between 200,000 and 100,000 years ago in Africa. Such fossils as the Atapuerca skull and the Kabwe skull bear witness to the two branches of the H. heidelbergensis tree.
http://en.wikipedia.org/wiki/Species
and especially the subsection, "Definition of Species", and then on the redirect section on "Species Problem"
http://en.wikipedia.org/wiki/Species_problem
For the most part I am one of the adherants of the point of view that the definition of species should be measured by a fixed unit of genetic distance, as much as possible. My working definition is that a million years' worth of evolutionary divergence equals a clear distinction between species. Most workers are vague about the distinction between species and subspecies: I personally regard subspecies as an arbitrary unit, which is useful to field ecologists but not of any value as a taxonomic grade. That part is not important in this discussion.
The Wikipedia article has a chart of species, which are estimated to be still awaiting discovery. That chart is attached in this article and the discovery of new animal species is exactly what cryptozoology is all about. Something like 61,000 species of vertebrates are awaiting discovery by the chart, which would include quite a few large land and s
ea mammals, on the usual flat cross-section percentage. The number of mammal species alone could number in the tens of thousands, and the number of LARGE mammal species yet to be discovered in the thousands, and still be only a very small cut out of that estimated figure.Now my own expertise is in physical anthropology and to be precise, the measurement and comparison of fossil hominin skulls. I have several times made the statement that even if most wildmen reported are relic hominids, they could still be members of the same species as us. Here is a section out of the Wikipedia article on Homo heidelburgensis:
http://en.wikipedia.org/wiki/Homo_heidelbergensis
Divergent evolution
Most experts now agree that H. heidelbergensis is the direct ancestor of H. sapiens (with some uncertainty about such specimens as H. antecessor, now largely considered H. heidelbergensis) and H. neanderthalensis. Because of the radiation of H. heidelbergensis out of Africa and into Europe, the two populations were mostly isolated during the Wolstonian Stage and Ipswichian Stage, the last of the prolonged Quaternary glacial periods. Neanderthals diverged from H. heidelbergensis probably some 300,000 years ago in Europe, during the Wolstonian Stage; H. sapiens probably diverged between 200,000 and 100,000 years ago in Africa. Such fossils as the Atapuerca skull and the Kabwe skull bear witness to the two branches of the H. heidelbergensis tree.
Homo neanderthalensis retained most of the features of H. heidelbergensis after its divergent evolution. Though shorter, Neanderthals were more robust, had large brow-ridges, a slightly protruding face and lack of prominent chin. They also had a larger brain than all other hominins. Homo sapiens, on the other hand, has the smallest brows of any known hominin, was tall and lanky, and had a flat face with a protruding chin. H. sapiens has a larger brain than H. heidelbergensis, and a smaller brain than H. neanderthalensis, on average. To date, H. sapiens is the only known hominin with a high forehead, flat face, and thin, flat brows.
[And to this we can add, the only hominin KNOWN to have lost the hirsute coat of body hair-DD]
Some believe that H. heidelbergensis is a distinct species, and some that it is a cladistic ancestor to other Homo forms sometimes improperly linked to [called a] distinct species in terms of populational genetics.
Some scenarios of survival include
H heidelbergensis > H. neanderthalensis
H. heidelbergensis > H. rhodesiensis > H. sapiens idaltu > H sapiens sapiens
H heidelbergensis > H. neanderthalensis
H. heidelbergensis > H. rhodesiensis > H. sapiens idaltu > H sapiens sapiens
Those supporting a multiregional origin of modern humans envision fertile reproduction between many evolutionary stages and homo[lateral] walking, or gene transfer between adjacent populations due to gene passage and spreading in successive generations.
--This I would call a fair statement all around with the glaringly obvious (to me) amendment that the time of divergence between H. sapiens and H. neandethalensis from the common ancestral stock (H. heidelbergensis including H. antecessor) is not long enough to create distinct species. It is a fair statement to say that the anatomy does display speciation in process, but all would be the same species and that species' name would be Homo sapiens by priority. 200,000 to 300,000 years' worth of genetic distance is nowhere near enough to consider any two other animal species as sufficiently divergent to qualify for separate species status.
This message encountered transmission difficulties when I sent it to Jon. I sent a second message for clarification but there is still one statement which should be changed. The line in this version says "The number of large mammal species alone could be in the tens of thousands" and it should have read "the number of mammal species alone could number in the tens of thousands, and the number of LARGE mammal species yet to be discovered in the thousands"
ReplyDeleteAnd I know even after that adjustment, the statement is liable to draw fire. Those are not MY figures, I am merely drawing attention to the figures that were posted.