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#4:
Fue mas o menos el 13 de marzo de 2004, los hombres fueron para un lado y los monos empezaron a hablar de conspiraciones...
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Fue mas o menos el 13 de marzo de 2004, los hombres fueron para un lado y los monos empezaron a hablar de conspiraciones...
#5 Esto pone en esa dirección: http://www.sciencemag.org/cgi/content/full/312/5776/985a
Science 19 May 2006:
Vol. 312. no. 5776, pp. 985 - 986
DOI: 10.1126/science.312.5776.985a
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News of the Week
HUMAN EVOLUTION:
Genomes Throw Kinks in Timing of Chimp-Human Split
Elizabeth Pennisi*
A new genomic analysis has added a provocative twist to the history of humans. After comparing the genomes of five primate species, researchers have concluded that the ancestors of chimps and humans went their separate ways about 6 million years ago–at least a million years later than fossils suggest. But that's not even the most controversial claim: Early hominids interbred with their chimp cousins, says David Reich, a geneticist at Harvard Medical School in Boston. This hybridization helped make the human genome a mosaic of DNA with varying degrees of similarity to the chimp genome, he and his colleagues report in a paper published online on 17 May by Nature.
Figure 1 Human roots. New DNA studies challenge the hominid status of the 7-million-year-old Toumaï fossil (bottom) by suggesting that humans (top) and chimps (middle) diverged much more recently.
CREDITS (TOP TO BOTTOM): PHOTOS.COM; DORLING KINDERSLEY/GETTY IMAGES; MPFT
Researchers are impressed by the huge amount of data Reich, Nick Patterson of the Broad Institute in Cambridge, Massachusetts, and their colleagues incorporated into their study. "The paper showed that the comparative genomic approach is very powerful," says geneticist Hideki Innan of the University of Texas Health Science Center in Houston. But some, particularly paleontologists whose fossils suddenly might become too old to be hominids, are more critical. Martin Pickford of the Collège de France in Paris predicts that the work will be "of passing significance."
For decades, anthropologists have argued about the timing of the chimp-human split, with estimates ranging from 10 million to 5 million years ago. The oldest fossil put forth as a human ancestor is a spectacular skull unearthed in Chad in 2002 nicknamed Toumaï. It dates back 7 million years, says co-discoverer Michel Brunet of the University of Poitiers, France. Two other hominid species were alive in Kenya and Ethiopia 5.8 million to 6 million years ago, according to other fossils.
This fossil record doesn't neatly fit with the new findings by Reich's team. They matched up DNA sequences from the human, chimp, orangutan, macaque, and gorilla genomes and documented the differences. Having DNA from the orangutan, and from an even less related species, the macaque, allowed the group to confirm that mutations accumulated at about the same rate in different lineages of apes and humans. This meant that the number of differences in each lineage could be compared directly and were reliable for calculating how long the branches between apes and humans on the tree should be.
The sequence comparisons provided relative "genetic" ages of the five species, and based on the ages of fossils of the ancestors of orangutans and macaques, the investigators concluded that the human lineage split from chimps no more than 6.3 million years ago and perhaps even more recently than 5.4 million years ago. That timing roughly agrees with another genetic analysis, reported in December 2005, by Blair Hedges, an evolutionary biologist at Pennsylvania State University in State College. "Together, they make a strong argument against the claims of older divergence times by paleontologists and other molecular evolutionists," says Hedges.
Brunet counters that it's too early to rewrite human history based on the DNA data. "Their explanation is just a hypothesis, while Toumaï is a true fossil," he says. Also, the difference between the dates from the molecular analyses and the age of the Chad fossil may not be significant. "There are broad confidence limits on genetic data," says Montgomery Slatkin, a population geneticist at the University of California, Berkeley.
But no matter when hominid speciation occurred, the genetic analysis revealed that the transition wasn't very smooth. By comparing discrete sections of the primate genomes, Reich's team was able to calculate at least a 4-million-year difference in the ages of the oldest and youngest parts of the human genome. The X chromosome's age was most surprising. Chimp and human X chromosomes are much more similar than are the rest of their chromosomes, says Reich. Based on this congruency, he and his colleagues calculate that the X chromosomes became species-specific 1.2 million years after the rest of the genomes.
To explain this oddity, Reich proposes that after evolving their separate ways for an unknown length of time, the earliest hominids and chimps hybridized. To be fertile, the hybrids had to have compatible X chromosomes, and thus there was intense selection to weed out any differences on that chromosome. Only after hybridization ceased did the X chromosome evolve into two different ones again.
Innan's analysis of just human and chimp DNA, published earlier this month in Molecular Biology and Evolution, supports the idea of hybridization between chimp and human ancestors. Still, Reich theory's is getting a tough reception. "I don't buy these hybrids," says Harvard anthropologist David Pilbeam, arguing that the ancestors of hominid and chimp were too different, morphologically and developmentally, to produce fertile offspring.
As more primate genomes are sequenced, the history of the X chromosome should become clearer, says Reich. Whether chimp ancestors interbred with human ancestors or not, notes Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, comparative genomics "tells us … things that paleontology can't."
#1 ¿Cuál no te deja? Yo puedo ver todos (paga la uni)
Chico mono busca chica mona
Pozí... a mi todavía me gustan las tías monas
eso no es nada nuevo!yo cuando i a Bush ya lo supe...(lo unico que no lo voy gritando por ahi)
Por lo visto en el partido Betis-Sevilla de ahora mismo hay un especimen que todavía no tiene los genes separados
Pero que herejes que somos.
Meneo.
el momento exacto.. antes/despues.. creo que el estudio genetico es mas exacto que el paleontologo, bueno.
al margen: el articulo de 20minutos referencia a un articulo de siencia magazine, en ingles, de donde han sacado casi todo el texto, no importa, el caso es que este articulo a su vez referencia a otro y este ultimo al intenta verlo dice:
YOU DO NOT HAVE ACCESS TO THIS ITEM (es de pago)
y te deja la lectura a la mitad, en fin
es este:
HUMAN EVOLUTION:
Genomes Throw Kinks in Timing of Chimp-Human Split
en esta direccion:
http://www.sciencemag.org/cgi/content/full/312/5776/985a
que es donde aparace el formulario de registro
gracias natrix
: )
quedo en deuda con tigo
De eso no cabe duda...