1 March 2007

Doch noch nicht so lange her?

Aus ScienceNow (27 February 2007; nicht frei erhältlich):
A Recent Split of Humans and Chimps?

By Ann Gibbons
ScienceNOW Daily News

In recent years, paleoanthropologists have been closing in on the exact time and place where the ancestors of humans and chimpanzees went their separate ways. As they uncovered several types of fossils from the dawn of humankind, they proposed that these early hominids lived between 5 million and 7 million years ago--dates that match up nicely with molecular studies. Now, however, this satisfying consensus is being challenged by a new study that proposes a surprisingly recent separation.

In a report published online in the February issue of PLoS Genetics [Hobolth et al. (2007), Genomic Relationships and Speciation Times of Human, Chimpanzee, and Gorilla Inferred from a Coalescent Hidden Markov Model; Volltext frei erhältlich], Danish postdoctoral researcher Asger Hobolth of North Carolina State University in Raleigh and his colleagues compared 1.9 million basepairs of DNA in four regions of the genomes of humans, chimpanzees, gorillas, and orangutans. They then used a well-known statistical method called the hidden Markov model, which was developed in the 1960s for speech recognition, to help them identify subtle patterns in the genomes of apes and humans. [...]

More to the point, the researchers could then calculate the order--and relative timing--in which various lineages split apart on the primate family tree, with orangutans appearing first, followed by gorillas, chimps, and then humans. They dated the branching points by using fossils of orangutan ancestors, which were 18 million years old, to set a starting time at the base of the tree for a "molecular clock." Although molecules mutate at various rates, the average is relatively constant if enough time passes--and those mutations can be used like a clock to date how long ago two species split. The team ended up with a date of 4.1 million plus or minus 400,000 years for the human-chimp split. It was so recent it even surprised the authors, says Hobolth.

Some researchers say the date is so recent, something must be wrong with this application of the Markov methodology. It would bump all the earliest fossils out of the human tree--including a 4.1-million-year-old fossil from Kenya called Australopithecus anamensis, which was already well on its way toward becoming human; it already walked upright, which is a defining character of being ancestral to humans, but not apes. "A 4.1-million-year split for humans and chimps ... is hard to defend because fossils practically reject it," says evolutionary biologist Blair Hedges of Pennsylvania State University in State College. [...]
Echt spannend.
Der letzte Abschnitt zeigt auch schön, dass es keineswegs so ist, wie Kreationisten oder IDler gerne behaupten, *nichts* würde veröffentlicht, das "die herrschende Lehrmeinung" angreift oder sonst wie kontrovers ist.
Zum Beispiel hier (Institute for Creation Research):
Their [Anm.: scientists] scientific method involves careful testing and replication of experimental data, without regard to personal beliefs.

Such ideals are not always attained, unfortunately. Scientists are fallible, sinful human beings, just like everyone else. Often they are downright bigoted, especially when asked to consider a concept outside their naturalistic worldview. Their process of "peer review" screens out all other worldviews and any data which support them.

(Man beachte auch den Gebrauch des paranoiden "THEM" (siehe Evil Atheist Conspiracy) - dabei behaupten sie doch, dass sie selbst Wissenschaftler sind.)

Ich würde jedenfalls sagen, das kontroverse (und gut belegte - daran scheiterts nämlich tatsächlich bei "IHNEN") Ergebnisse eine ausgezeichnete Chance haben, in wirklich guten Journals eine Veröffentlichung oder Erwähnung zu bekommen.


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