Topic: Some human evolution articles.

[Nemesis]

Link to Neanderthal article

Preliminary analysis shows the bundle of DNA responsible for maleness in the Neanderthal - its Y chromosome - is very different from modern human and chimpanzee Y chromosomes; more so than for the other chromosomes in the genome.

This might suggest that little interbreeding occurred between our own species and the Neanderthals.

Link to first chimp article

The best explanation for these surprising findings - the relatively young and variable divergence dates between the human and chimp lineages, and the evidence for strong selection on the X chromosome - would be if the two lineages split sometime before the time of the first proto-human fossils, but later rehybridised (see Diagram) in a "reverse speciation" event (see "When evolution runs backwards"). Natural selection would favour those hybrid individuals whose X chromosomes carried fewest of the genes that lower fertility.

So far, Reich admits, this is only a plausible hypothesis, not a proven fact. For example, he calibrated his molecular clock using the divergence time between humans and macaques, which is estimated at no more than 20 million years ago. If this divergence happened earlier, that would push back the human-chimp split to an earlier date as well - perhaps far enough that there would be no need to invoke hybridisation. At the very least, though, Reich's study shows that the separation between humans and chimps was a long, drawn-out process.

Link to second chimp article

Past studies that compared human and chimp DNA could only offer a point estimate of how long ago the two species split by averaging the amount of divergence in their genes. Generally, those studies come up with a figure of about seven million years ago.

But since the completion of the chimpanzee genome project in September it is possible to look at how specific sections of the genetic code have evolved. The Broad Institute study, which will be published in a future issue of the journal Nature, is one of the first to do that.

Some interesting ideas. 

[Nemesis]

Homo floresiensis 3 article links debating new species or not.

Link 1

"Some of the material [at Liang Bua] is believed to go back to 70,000 years and the most recent material to 12,000 years. We're not talking about one individual at one point in time. This morphology is represented over a considerable period in time," he said.

Dr Martin also challenges Professor Falk's comparison of the adult LB1 with a specimen from a 10-year-old microcephalic. He contends the Indonesian example should have been matched against individuals with a mild form of microcephaly that permitted survival into adulthood.

The Field Museum researcher provides his own microcephalic specimens by way of comparison. But in their response, Dr Falk and colleagues described Dr Martin's comparison as "inadequate" and lacking "crucial details".

Link 2

"This defective plaster copy of a microcephalic skull used in the study by Falk et al., published in Science March 4, 2005, is inappropriate for any scientific study, especially one dealing with a topic as demanding and high-profile as this one," Dr. Martin says. "Quite simply, it was the worst possible choice for this study. The cranial capacity turned out to be only 260 cc, just over half of that recorded for the LB1 skull, and is one of the smallest that I have so far found in a survey of over 100 human microcephalics."

This leaves the theory that LB1 was a microcephalic modern human as the only plausible explanation for the Flores fossils, according to Drs. Martin and Phillips and their colleagues.

Link 3

“Although we only have one cranium,” says Morwood, “the other bones we found show that LB1 was a normal member of an endemically dwarfed hominid population.” The distinctive traits of reduced body mass, reduced brain size and short thick legs mirror those found in other island endemic populations of large mammals, Morwood says. He calls the microcephaly explanation “bizarre”. It ignores other evidence from Liang Bua and the literature on island endemic evolution, he says.

[Nemesis]

Link to full article

"What was very clear from my perspective looking at the Hobbit's wrist bones is that it does not belong in the group that includes modern humans and Neanderthals. It basically has the same type of wrist that we see in [the ancient hominid] Homo habilis, that we see in Australopithecus (the famous 'Lucy' fossil) and that we see in living chimps and gorillas today," Matthew Tocheri told BBC News.

[Nemesis]

Just read through the Scientific American special edition "What makes us Human?"  Some interesting articles.

The article on Homo Floresiensis claims it is not a dwarfed Homo Erectus but an offshoot from an earlier time.  Possibly immediately before or after Homo Habilis.  Details of the wrist, legs and feet are wrong for Erectus - too ape like.

The brain investigations show one over sized lobe that is believed to contribute heavily to more abstract thought which would explain its relatively advanced stone work in spite of a chimp sized brain. 

The big discussion on that topic is how it got there as it is too primitive to have spread that far.  Strangely they don't have any trouble with the even more "primitive" ancestor of the Orangutans spreading to Sumatra and Borneo from Africa which is nearly as far.  Worse for the Orangutan spreading is it is primarily arboreal where the so called Hobbit is not. 

[knightstorm]

Well, this article seems to suggest the opposite regarding human/neanderthal hybridization
http://www.sciencemag.org/content/328/5979/710

Regarding floriensis, one problem with identifying an earlier hominid as its ancestor is the lack of a fossil record.  If an earlier homo made its way across Asia, why aren't there any fossils of it?

[Starfox1701]

Fossilization is not an exact process  and when the time scale of human evolution is taken into consideration it is considerably shorter then the age of dinosaurs for example. It is not without reason that whole evolutionary populations have passed beyond the veil and we will never find fossil evidence of them. As much as we like to think of ourselves as the great sharpers of our world humanities works are not more durable the the great mountain ranges or dead rivers of the past. It is only by the great luck that we have the scattered clues of our own past  that we now hold. And so we look at the great puzzle of our own evolution with only a fraction of pieces needed to see the whole of it.

[Nemesis]

Most creatures don't leave fossils.  If Homo Floresiensis lived in the "wrong" type of environment to leave fossils normally then there will be very few.  Especially few if their population was low and only present in an area for a short time.  In addition their bones are fairly fine and fragile much less likely to survive intact.

However there may in fact be fossils just misidentified.  Consider Denisova woman the finger bone that was found could easily be mistaken for other hominids such as Sapiens or Neandertal.  Only a genetic analysis showed it to be of a different species.  Partial remains of the Hobbits would easiy be mislabeled based on the found portions.  Ape feet, wrists and shoulder blades. 

[intermech]

I'm not an evolutionist, so I am trying to better understand what I am reading here. It looks to me like generally they are thinking some of these species are chronologically parallel rather than as linear as they thought.

[Nemesis]

Don`t forget that a species may split in 2 and the original species continues as does the new species. 

[knightstorm]

I'm not an evolutionist, so I am trying to better understand what I am reading here. It looks to me like generally they are thinking some of these species are chronologically parallel rather than as linear as they thought.

Which articles are you referring to?

[Starfox1701]

Don`t forget that a species may split in 2 and the original species continues as does the new species.

This is likely more true then you realize. It is both possible and probable that the various strains of human ancestors battled each other for territory and resources. It is also likely that they interbred with each other captured females and young further spreading genetic diversity amongst these groups and creating new branches on the tree in the same way they did in more recent times. Such is the nature of our race.

[Nemesis]

Homo Sapiens
Neandertal
Denisovans
Homo Idalto
Homo Floriensis

5 known already overlapping I wouldn't be surprised at more.  Also would be surprised if earlier forms didn't overlap each other. 

[knightstorm]

The brain investigations show one over sized lobe that is believed to contribute heavily to more abstract thought which would explain its relatively advanced stone work in spite of a chimp sized brain. 

Or, the tools could have been left by subsequent AMH inhabitants in the cave, or the hobbits could have mimiced AMH stonework, or possibly even stolen tools from AMHs.

[Nemesis]

The tools seem to predate modern human presence on the island.

[Nemesis]

Link to full article

Argue and her team studied 133 different characteristics of the Homo floresiensis skull, jaw, teeth, shoulders, legs and arms, and compared them to all other known hominid species.

They found that it's a long-surviving cousin of Homo habilis, an early human ancestor with roots in Africa. None of their tests yielded evidence to support the theory that Homo floresiensis evolved from Homo erectus.

"These two species are most likely to have shared a unique common ancestor that was not shared with any other species in our analysis," she said. "But [Homo floresiensis] lived half a world away, and is separated in time by maybe two million years."