Hominin fossils discovered near the site of the ‘hobbit’ Homo floresiensis provide yet more evidence that the human lineage is more diverse than was ever imagined.
Arthur C. Clarke wrote in 2001: A Space Odyssey that behind every person now living stand 30 ghosts, for that is by how many the dead outnumber the living. That was in 1968 — the number reckoned today would probably be greater. The human lineage diverged from that of chimpanzees some 5 million to 7 million years ago. Were we able to mark the remains of all our ancestors from that point, the world would be one enormous cemetery.
The most likely fate of any living organism is dissociation into its component molecules, if not reabsorption as food into something else. That makes the chance ineffably remote that the remains of any one individual will be fossilized in any recognizable form, and, this having been achieved, be recognized as such by a passing palaeontologist before the fossil, too, crumbles to dust.
It is possible that many human species once existed, but became extinct with such finality that even those few that were fossilized have since disappeared, leaving absolutely no trace that generations of a distinct species lived and died on this planet — a kind of double extinction, without hope of memorial or discovery. Fossils from the human lineage are scarce, and, given the numbers that must once have lived, the percentage recovered must hardly be significantly different from zero. (You can read about some of those that have been found in our Nature collection at go.nature.com/1zjssjs.)
Long-lost relations
Hence the surprise when, in 2004, a group of scientists in Indonesia and Australia announced the discovery of what became known as Homo floresiensis, a species of unusual, dwarfed hominin — that is, a creature living or extinct more closely related to us than to chimps — whose remains were found in Liang Bua cave on the island of Flores in Indonesia (P. Brown et al. Nature 431, 1055–1061; 2004).
There was some doubt at the time that H. floresiensis represented a real species rather than a variant of modern humans affected by some disease or pathological condition, but this dissent was gradually eroded, not only by a long palaeontological record at Liang Bua, but also by a rich archaeological record in the island’s Soa Basin, some distance to the east, showing that hominins of some sort had lived in the region for up to one million years (A. Brumm et al. Nature 464, 748–752; 2010). Yet direct evidence, in the form of bones and teeth, was elusive. Until now.
In this week’s issue, researchers report a fragment of mandible and six isolated teeth of hominins from Mata Menge in the Soa Basin that they describe as similar to those of H. floresiensis, but more primitive in some respects and — if anything — even smaller. In an accompanying paper, they show that the remains were deposited 700,000 years ago, many thousands of years before those from Liang Bua.
The researchers take the appropriately cautious and parsimonious view that these hominins were most closely related to early Asian Homo erectus, on the grounds that this is the only species of hominin otherwise known to have inhabited that part of the world at that time. However, it remains possible, as an accompanying News & Views explains, that these creatures might represent some very early, pre-H. erectus exodus from Africa. If so, that expands our ignorance from a barely manageable ocean into a gulf of interstellar magnitude, implying that a wholly unknown plethora of hominins lived in Eurasia millions of years earlier than anyone suspected, just one of whose number has been found in the region’s southeastern extremity to betray the possibility that such an array of species ever existed.
Is this unwarranted speculation? Perhaps not: the discovery of H. floresiensis prompted a sea change in palaeoanthropologists’ attitudes to the unknown. Researchers are less eager than they once were to string fossils together into confident chains of ancestry and descent. They are more likely to reappraise the various oddities of human evolution, no longer dismissing them as fossils that are hard to fit into the current paradigm of ancestry and descent, but seeing them as representatives of entirely unsuspected branches of the human family tree. One thinks of the many hominin remains recovered over the past few decades from China, some of which do not quite fit into any current species. Or of Homo heidelbergensis, an increasingly unwieldy catch-all for hominins from the Middle Pleistocene epoch (781,000–126,000 years ago); or of H. erectus itself, a grouping of such variety that some have found it hard to accept that all the fossils ascribed to it comprise a single species. And there are others less familiar, such as skulls from Iwo Eleru in Nigeria that look surprisingly archaic, despite being assigned a relatively recent date of as few as 11,700 years ago (K. Harvati et al. PLoS ONE 6, e24024; 2011).
Studies on human DNA, ancient and modern, have reinforced this trend. The recovery of an entire genome of a hitherto unknown archaic hominin from a single finger bone from Denisova Cave in Siberia was — and is — an astonishing achievement, both for the discovery itself and for its implications (D. Reich et al. Nature 468, 1053–1060; 2010). It reinforces hints that the scarcity of human fossils belies what might once have been hitherto unimaginable diversity. The finding, reported in the same paper, that Denisovan DNA lives on in people from southeast Asia and the western Pacific, just as Neanderthal DNA survives in Eurasians generally, proves that fossils tell us much less than we would like of the human career. And as with Iwo Eleru, so with DNA: there are signs that the genomes of some modern Africans contain elements derived from archaic hominins not found in the fossil record (M. F. Hammer et al. Proc. Natl Acad. Sci. USA 108, 15123–15128; 2011).
These early human relatives left signs of their passing as evanescent and enigmatic as the Cheshire Cat from Alice’s Adventures in Wonderland — slowly fading from view, with just its smile hanging on, until that, too, disappears.
Nature 534, 151 (09 June 2016) doi:10.1038/534151a
lunes, 8 de agosto de 2016
miércoles, 20 de julio de 2016
Información ancestral en el cerebro
La geometría de la superficie cortical humana contiene abundante información ancestral. En concreto, las circunvalaciones y los surcos de la corteza cerebral son las estructuras que aportan más datos. Investigadores de la Universidad de California en San Diego compararon las segmentaciones superficiales, los giros y surcos del cerebro de más de 500 jóvenes con su herencia genética.
Hallaron que los sujetos cuyos antepasados procedían de poblaciones primitivas norteamericanas presentaban curvaturas frontales y occipitales aplanadas. Los patrones anatómicos del cerebro de otros participantes situaban sus raíces en África Occidental, Asia Oriental o Europa.
Las imágenes muestran los prototipos corticales que Chun Chieh Fan y sus colaboradores determinaron para los linajes genéticos de estas cuatro partes del mundo. Las líneas de colores indican el contorno tridimensional de la corteza cerebral de los diferentes grupos de población, además de representar la dimensión espacial (longitudinal, sagital o transversal) hacia la que se han desplazado los vértices de los respectivos repliegues.
Los autores no encontraron ninguna relación entre la forma del cerebro de los probandos y sus respectivas capacidades cognitivas. En otras palabras, la geometría cerebral no tiene nada que ver con la inteligencia.
Fuente: «Modeling the 3D geometry of the cortical surface with genetic ancestry». C. Fun et al., en Current Biology, vol. 25, n.o 15, págs. 1988-1992, 2015
miércoles, 29 de junio de 2016
‘Hobbit’ relatives found after ten-year hunt
Jaw and teeth discovered in Indonesia are triumph for team that almost gave up hope.
Ewen Callaway
More than a decade after the discovery that a diminutive relative of modern humans once lived on the Indonesian island of Flores, Gerrit van den Bergh was losing faith that he would find any clues to the ancestors of the ‘hobbit’. It was October 2014, and for four years he had co-led an industrial-scale excavation near the cave where the metre-tall skeleton had been found. Then, weeks before packing it in for the year, a local worker found a 700,000-year-old molar. More teeth and a partial jaw quickly followed.
“We had given up hope we would find anything, then it was ‘bingo!’,” says van den Bergh, a palaeontologist at the University of Wollongong, Australia, whose team reports the finds in two papers in this issue (G. D. van den Bergh et al. Nature 534, 245–248; 2016; and A. Brumm et al. Nature 534, 249–253; 2016). “We had this enormous party. We had a cow slaughter and there was dancing. It was marvellous.”
The unusually petite jaw and teeth are from at least one adult and two children — the first possible ancestors of Homo floresiensis ever to be discovered — and resemble the hobbit remains found on the island, which are between 60,000 and 100,000 years old.
The jaw and teeth address two questions that have dogged the study of the species — where did it come from and how did it get so small? But as with all things hobbit, there is little consensus among researchers, who say that firm conclusions require more fossils.
The hobbit’s discovery in 2003 in Liang Bua cave, by a team led by the late Australia-based rock-art specialist Mike Morwood, was an instant sensation. But its place in the human family tree is contentious. Morwood’s team proposed that it was a shrunken Homo erectus, the same species that probably evolved into Homo sapiens in Africa and that roamed as far as Europe and Asia. Other scientists who have examined features of H. floresiensis, such as its long, flat feet, think that it descended from a smaller, more primitive human relative such as Homo habilis or even Australopithecus, known only from remains in sub-Saharan Africa.
Seeking the hobbit’s ancestors, in 2004, Morwood’s team returned to a site 74 kilometres from Liang Bua called Mata Menge, where elephant bones and tools had been found in the 1960s. The dig started small, but in 2010 the team scaled up. Bulldozers cleared an area of 2,000 metres square, and more than 100 locals then dug for 6 days a week using chisels and hammers. They found hundreds of stone tools, thousands of fossils from animals such as crocodiles, rats and komodo dragons, but no hominin bones.
By then ill with advanced prostate cancer, Morwood visited the area for the last time in 2012. “He really made an effort to walk through the site, you could see he was in pain, but he was so detailed-minded,” van den Bergh says. “He increased the pressure to dig more holes and go faster. He really wanted to find them.”
Morwood, who died in 2013 before the teeth and jawbone were found, is an author on the Nature papers, which were co-led by scientists based in Japan, Australia and Indonesia.
The team concludes that the jaw excavated at Mata Menge is from an adult (its wisdom tooth had erupted) who was even smaller than the hobbit, and that two canines are the milk teeth of two different children. The thin jaw looks more like that of H. erectus and H. floresiensis than the beefier jaws of more primitive hominins such as H. habilis. The square-shaped teeth are intermediate between H. erectus and H. floresiensis. One tooth and the rock around it led the team to estimate that the remains are some 700,000 years old. The oldest artefacts in the region, meanwhile, suggest that a group of Homo erectus arrived on Flores about one million years ago, says van den Bergh.
Dwarfed by diet
He and his team note that the remains point to large-bodied H. erectus as the likeliest ancestor of the hobbit, and propose that it became dwarfed in just a few hundred thousand years to cope with the meagre resources on Flores. Elephants and other large creatures have been known to shrink over time to cope with the lack of food typical of islands, and red deer on the island of Jersey in the English Channel became one-sixth of their original size in just 6,000 years, says van den Bergh.
Both Fred Spoor, a palaeontologist at University College London, and palaeoanthropologist Chris Stringer at London’s Natural History Museum agree that H. erectus is now the best fit for the hobbit’s ancestor, although Stringer isn’t so sure that the shrinkage happened on Flores. It’s just as likely that the hobbit emerged on another island, such as Sulawesi, and then moved to Flores, he says.
But William Jungers, a palaeoanthropologist at Stony Brook University in New York, says that the fossils are not complete enough to favour the H. erectus origin: “I don’t believe these scrappy new dental specimens inform the competing hypotheses for the origin of the species one way or another.”
A small river that leads down a hill deposited the sandstone in which the teeth and jaw were found, and van den Bergh expects that more hominin remains lie there. His colleagues, meanwhile, have found stone tools in Sulawesi, north of Flores. For once, the prospect of more hobbits isn’t looking so bleak.
Nature 534, 164–165 (09 June 2016) doi:10.1038/534164a
Tomado de: http://www.nature.com/news/hobbit-relatives-found-after-ten-year-hunt-1.20045?WT.ec_id=NEWS-20160609&spMailingID=51569420&spUserID=NDE2OTkzMjMwMjMS1&spJobID=941259260&spReportId=OTQxMjU5MjYwS0
Ewen Callaway
More than a decade after the discovery that a diminutive relative of modern humans once lived on the Indonesian island of Flores, Gerrit van den Bergh was losing faith that he would find any clues to the ancestors of the ‘hobbit’. It was October 2014, and for four years he had co-led an industrial-scale excavation near the cave where the metre-tall skeleton had been found. Then, weeks before packing it in for the year, a local worker found a 700,000-year-old molar. More teeth and a partial jaw quickly followed.
“We had given up hope we would find anything, then it was ‘bingo!’,” says van den Bergh, a palaeontologist at the University of Wollongong, Australia, whose team reports the finds in two papers in this issue (G. D. van den Bergh et al. Nature 534, 245–248; 2016; and A. Brumm et al. Nature 534, 249–253; 2016). “We had this enormous party. We had a cow slaughter and there was dancing. It was marvellous.”
The unusually petite jaw and teeth are from at least one adult and two children — the first possible ancestors of Homo floresiensis ever to be discovered — and resemble the hobbit remains found on the island, which are between 60,000 and 100,000 years old.
The jaw and teeth address two questions that have dogged the study of the species — where did it come from and how did it get so small? But as with all things hobbit, there is little consensus among researchers, who say that firm conclusions require more fossils.
The hobbit’s discovery in 2003 in Liang Bua cave, by a team led by the late Australia-based rock-art specialist Mike Morwood, was an instant sensation. But its place in the human family tree is contentious. Morwood’s team proposed that it was a shrunken Homo erectus, the same species that probably evolved into Homo sapiens in Africa and that roamed as far as Europe and Asia. Other scientists who have examined features of H. floresiensis, such as its long, flat feet, think that it descended from a smaller, more primitive human relative such as Homo habilis or even Australopithecus, known only from remains in sub-Saharan Africa.
 |
| The late rock-art specialist Mike Morwood at Liang Bua cave, where his team discovered Homo floresiensis. |
By then ill with advanced prostate cancer, Morwood visited the area for the last time in 2012. “He really made an effort to walk through the site, you could see he was in pain, but he was so detailed-minded,” van den Bergh says. “He increased the pressure to dig more holes and go faster. He really wanted to find them.”
Morwood, who died in 2013 before the teeth and jawbone were found, is an author on the Nature papers, which were co-led by scientists based in Japan, Australia and Indonesia.
 | ||
| G. D. van den Bergh et al. | The jaw bone found on Flores is from an adult who was even smaller than the hobbit. |
Dwarfed by diet
He and his team note that the remains point to large-bodied H. erectus as the likeliest ancestor of the hobbit, and propose that it became dwarfed in just a few hundred thousand years to cope with the meagre resources on Flores. Elephants and other large creatures have been known to shrink over time to cope with the lack of food typical of islands, and red deer on the island of Jersey in the English Channel became one-sixth of their original size in just 6,000 years, says van den Bergh.
 | ||
| G. D. van den Bergh et al. | Teeth found at the Mata Menge site |
Both Fred Spoor, a palaeontologist at University College London, and palaeoanthropologist Chris Stringer at London’s Natural History Museum agree that H. erectus is now the best fit for the hobbit’s ancestor, although Stringer isn’t so sure that the shrinkage happened on Flores. It’s just as likely that the hobbit emerged on another island, such as Sulawesi, and then moved to Flores, he says.
But William Jungers, a palaeoanthropologist at Stony Brook University in New York, says that the fossils are not complete enough to favour the H. erectus origin: “I don’t believe these scrappy new dental specimens inform the competing hypotheses for the origin of the species one way or another.”
A small river that leads down a hill deposited the sandstone in which the teeth and jaw were found, and van den Bergh expects that more hominin remains lie there. His colleagues, meanwhile, have found stone tools in Sulawesi, north of Flores. For once, the prospect of more hobbits isn’t looking so bleak.
Nature 534, 164–165 (09 June 2016) doi:10.1038/534164a
Tomado de: http://www.nature.com/news/hobbit-relatives-found-after-ten-year-hunt-1.20045?WT.ec_id=NEWS-20160609&spMailingID=51569420&spUserID=NDE2OTkzMjMwMjMS1&spJobID=941259260&spReportId=OTQxMjU5MjYwS0
lunes, 27 de junio de 2016
Los chimpancés que jugaban con «muñecas» … de piedra
¿A qué niña no le gusta jugar con muñecas? ¿A qué niño no le gustan los Playmobil o las figuritas de superhéroes como Spiderman y Batman? Tanto en los días en los que Santa Claus o los Reyes Magos visitan los hogares humanos, como en cualquier aniversario o celebración que se precie, ambas preguntas tienen una clara respuesta. No es cuestión de género, pero no hay duda de que a los niños y niñas humanos les gustan los muñecos y las muñecas.
No obstante, pocos de nosotros nos paramos a pensar si este tipo de juego simbólico «tan humano» está ni siquiera presente en cualquier otra especie que no sea Homo sapiens. Pero la Primatología no deja de sorprendernos y el equipo del Prof. Richard Wrangham es uno de los responsables.
La primera ocasión fue el pasado 21 de diciembre de 2010. La prestigiosa revista Current Biology publicó la primera prueba documentada de juego con «muñecas/os» en chimpancés en libertad. Tal como comentan Richard Wrangham (Harvard University) y Sonya Kahlenberg (Bates College): «encontramos que los chimpancés juveniles tendían a llevar palos de una manera que sugería una muñeca rudimentaria, y que tal como sucede en animales cautivos y en niños, este comportamiento era más común en las hembras que en los machos».
Tomado de: http://www.investigacionyciencia.es/blogs/medicina-y-biologia/62/posts/los-chimpancs-que-jugaban-con-muecas-de-piedra-14175?utm_source=boletin&utm_medium=email&utm_campaign=Ciencias+sociales+-+Junio
No obstante, pocos de nosotros nos paramos a pensar si este tipo de juego simbólico «tan humano» está ni siquiera presente en cualquier otra especie que no sea Homo sapiens. Pero la Primatología no deja de sorprendernos y el equipo del Prof. Richard Wrangham es uno de los responsables.
La primera ocasión fue el pasado 21 de diciembre de 2010. La prestigiosa revista Current Biology publicó la primera prueba documentada de juego con «muñecas/os» en chimpancés en libertad. Tal como comentan Richard Wrangham (Harvard University) y Sonya Kahlenberg (Bates College): «encontramos que los chimpancés juveniles tendían a llevar palos de una manera que sugería una muñeca rudimentaria, y que tal como sucede en animales cautivos y en niños, este comportamiento era más común en las hembras que en los machos».
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| Elementos de madera utilizados como «muñecas» el el artículo original de Current Biology 2010. |
 |
| Chimpancé con bastón de madera. Fuente: Current Biology, 2010. |
Lejos de ser una conclusión precipitada o puramente anecdótica, el estudio se basó en 14 años de trabajo de campo con 68 chimpancés. Eran unos resultados realmente sorprendentes, no tanto por «descubrir» algo que se desconocía —ya había sido un comportamiento documentado de manera anecdótica en chimpancés cautivos— sino por documentarla en libertad, con una amplia muestra de individuos y con unas claras diferencias entre sexos para esta conducta.
Pero el estudio prosiguió y el equipo de Harvard ha continuado proporcionándonos sorpresas. En un reciente vídeo publicado en la web de la BBC, Wrangham explica la manera en la que los jóvenes chimpancés de los bosques de Uganda «juegan» con piedras como si de muñecos y muñecas se tratase. Los jóvenes chimpancés las manipulan y transportan durante unos pocos minutos o incluso durante horas. Las llevan con ellos mientras comen y mientras trepan por los árboles y las ramas. Acarrean con ellas incluso en los nidos, donde llegan a dormir junto a sus «muñecas de piedra».
Desde el punto de vista de Wrangham «este tipo de comportamientos es difícilmente comprensible si no asumimos que los jóvenes chimpancés tratan a esas piedras como si fueran bebés». De la misma manera que ocurría en el trabajo original publicado en 2010 con las «muñecas de madera», las hembras juegan con las piedras entre 3 y 4 veces más que los machos. Estas hembras dejan de jugar con las piedras en el momento que tienen a su primer bebé.
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| Secuencia de chimpancé jugando con una piedra. Fuente: BBC |
¿Es esta una nueva prueba de que la singularidad humana está en entredicho? Si bien puede ser un poco aventurado afirmarlo, sí que parece cierto que la «imaginación», el simbolismo y quizá la capacidad de abstracción a través del juego puede cumplir una función esencial en el desarrollo de habilidades fundamentales para la vida adulta como el hecho de ser madres y padres. ¿Significa además que las diferencias entre géneros tienen una base biológica y evolutiva? ¿Podemos seguir pensando que todas la diferencias de género han sido impuestas culturalmente? El debate está abierto.
Fuente: Citation: “Sex differences in chimpanzees’ use of sticks as play objects resemble those of children.” By Sonya M Kahlenberg and Richard W Wrangham. Current Biology, Vol. 20 Issue 24, Dec. 21, 2010.
Tomado de: http://www.investigacionyciencia.es/blogs/medicina-y-biologia/62/posts/los-chimpancs-que-jugaban-con-muecas-de-piedra-14175?utm_source=boletin&utm_medium=email&utm_campaign=Ciencias+sociales+-+Junio
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