miércoles, 26 de julio de 2006

Human Ancestors May Have Hit the Ground Running


New findings raise the interesting possibility that the step from a tree-dwelling ape to a terrestrial biped might not have been as drastic as previously thought.

Scientists find muscles gibbons use for climbing and swinging through trees might also help the apes run.

Humans are the upright apes, but much remains unknown as to how our ancestors first found their footing. To shed light on the past, Evie Vereecke at the University of Antwerp in Belgium and her colleagues looked at how modern cousins of humanity such as gibbons and bonobos amble.

For two months, Vereecke's team monitored how four white-handed gibbons at a local zoo strode at speeds ranging from strolls to sprints across a 13-foot-long walkway surrounded with video cameras and loaded with scientific instruments such as force plates and pressure mats.

The gibbons collaborated well, "especially when you rewarded them with some raisins," Vereecke said.

Walking vs. running

While bonobos are our closest relatives and probably have a similar anatomy to our ancestors, gibbons are the most bipedal nonhuman apes, and the researchers wanted to see whether their gaits resembled any of humans.

Walking saves energy by converting the kinetic energy from a step to potential energy as walkers move over their supporting feet, energy that is ready to get recovered back as kinetic energy when walkers move into their next step. Running, on the other hand, stores energy from each bound as elastic energy in the tendons, muscles and ligaments before it gets recycled back as recoil for the next step.

Most legged animals walk at low speeds and run, trot, hop or gallop at high speeds. By monitoring how much force the gibbons stepped down with, the researchers calculated that gibbons almost always seemed to bounce along using the energetics linked with running, even though their footfall patterns were more like those of walks, the scientists reported in the Journal of Experimental Biology.

This suggests the step for humans from a tree-dwelling ape to a terrestrial biped might not have been as drastic as previously thought, Vereecke said.

Hop on down

The bouncy energetics of running makes sense for tree-dwellers, since the stiff-legged motions often associated with walking can shake the unsteady branches the apes might find themselves on.

When it comes to how the ancestors of humans started on their legs, scientists are divided between the terrestrial theory, assuming we became bipedal through a four-legged stage on the ground, or the arboreal theory, that sees the biomechanics of climbing and swinging through trees as potential precursors for bipedalism.

These findings support the arboreal theory, although they do not exclude the terrestrial one.

By Charles Q. Choi
Special to LiveScience
posted: 24 July 2006
01:36 pm ET

Publicado en: http://www.livescience.com/animalworld/060724_gibbons_walking.html

Study hints language skills came early in primates


Tue Jul 25, 2006 10:48am ET

WASHINGTON (Reuters) - Language centers in the brains of rhesus macaques light up when the monkeys hear calls and screams from fellow monkeys, researchers said in a study that suggests language skills evolved early in primates.

Researchers who scanned the brains of monkeys while playing them various sounds found the animals used the same areas of the brain when they heard monkey calls as humans do when listening to speech.

Writing in this week's issue of the journal Nature Neuroscience , the international team of researchers said this finding suggests that early ancestors of humans possessed the brain structures needed for language before they developed language itself.

"This intriguing finding brings us closer to understanding the point at which the building blocks of language appeared on the evolutionary timeline," said Dr. James Battey, director of the National Institute on Deafness and Other Communication Disorders, which helped conduct the study.

"While the fossil record cannot answer this question for us, we can turn to the here and now -- through brain imaging of living nonhuman primates -- for a glimpse into how language, or at least the neural circuitry required for language, came to be."

The NIDCD's Allen Braun and colleagues trained rhesus monkeys to sit quietly in PET scanners. Positron emission tomography detects active cells and can be used to see which parts of the brain are working.

They played coos and screams made by rhesus monkeys that the test animals did not know, as well as "nonbiological sounds" such as music and computer-generated noises.

The monkey sounds activated areas of the brain corresponding to those used by humans in processing language -- known as Broca's area, and Wernicke's area, the researchers said.

In contrast, music and computer sounds mostly activated the brain's primary auditory areas.

"This finding suggests the possibility that the last common ancestor of macaques and humans, which lived 25 to 30 million years ago, possessed key neural mechanisms (that may have been used) ... during the evolution of language," the researchers wrote.

"Although monkeys do not have language, they do possess a repertoire of species-specific vocalizations that -- like human speech -- seem to encode meaning in arbitrary sound patterns."

For instance, many species of monkeys have calls to warn of danger from above, such as an eagle, calls referring specifically to leopards and also have various sounds used while socializing.

Publicado en: http://today.reuters.com/news/newsArticle.aspx?type=scienceNews&storyID=2006-07-25T144823Z_01_N25143557_RTRUKOC_0_US-SCIENCE-LANGUAGE.xml