ugnet_: The missing link

[J Ssemakula]

Image: COURTESY OF KALLIOPI MONOYIOS
April 02, 2004
Fossil Illuminates Evolution of Limbs from Fins
The discovery of a 365-million-year-old forelimb is helping scientists better understand how ancient creatures made the transition from water to land. A report published today in the journal Science describes the fossil, which represents an intermediate stage in the evolution of fish fins into vertebrate limbs. Neil H. Shubin of the University of Chicago and his colleagues recovered the bone, which was encased in a brick-size piece of red sandstone, from the side of a highway in north central Pennsylvania. The layered rocks are the remains of a stream system dating back to the Late Devonian Period. "We knew it was a humerus," study co-author Michael I. Coates of the University of Chicago recalls, "but it was an entirely different kind. We had never seen one like it before." For example, compared with the anatomy of other tetrapods of the same age there is a large space for chest muscle attachment, the scientists report. This added brawn would have enabled a motion similar to a benchpress or push-up. Based on the apparent size and extent of the muscles, the authors posit that the humerus played a significant role in the support and movement of the animal. The findings indicate that the ability to prop up the body is more ancient than previously believed. Says Coates, "This means that many of the features that we thought evolved to enable life on land originally evolved in fish living in aquatic ecosystems." Other fossils recovered from the same site indicate that the waterway was home to a variety of plant and animal life. The forelimb would have allowed the animal to propel itself along the bottom of the riverbed or elevate its head out of the water. In an accompanying commentary Jennifer A. Clack of the University of Cambridge notes that Devonian tetrapods "probably did not walk efficiently, but their modes of locomotion certainly varied, as they adapted skeletons and sensory organs for the challenges posed by emergence from the water." --Sarah Graham ------
March 31, 2004
Birds Share 'Language' Gene with Humans
The process by which baby birds learn to sing shares a number of traits with that by which toddlers learn to talk. Now researchers have identified a common gene between birds and people that underlies both abilities. The discovery marks the start of an effort to explore the genetic underpinnings of vocal learning. Vocal learning is characteristic of a number of animals, including humans, dolphins, whales and birds. To probe how genetics guides this process, Sebastian Haesler of the Max Planck Institute for Molecular Genetics in Berlin and Kazuhiro Wada of Duke University Medical Center and their colleagues focused on a gene known as FoxP2, mutatation of which is associated with language problems in people. "In affected humans, the mutation causes a very specific dysfunction," study co-author Erich Jarvis of Duke University explains. "These people have largely normal motor coordination, but an inability to correctly pronounce words or form them into grammatically correct sentences. What�s more, they have trouble understanding complex language." The team analyzed _expression_ of FoxP2 in a number of bird species, both vocal learners and nonlearners, and in crocodiles, the closest living relative of birds. In both humans and birds the gene is expressed in a brain region known as the basal ganglia, the researchers report today in the Journal of Neuroscience. "We found that the levels of FoxP2 seem to be increasing at times just before the bird begins to change its songs," Jarvis says. "So this is consistent with a cause-and-effect role, in which the gene switches on, allowing the song-learning circuitry to become more plastic, which allows the birds to imitate sounds." In nonvocal-learning species, in contrast, the team did not observe any localization or differential levels of FoxP2 activity. The team next plans to investigate whether there are small FoxP2 sequence differences between birds that learn to sing and those that do not, and study how mutations to the gene affect vocal learning. Other factors, such as connections between the brain and motor neurons controlling the voice, also contribute to vocal learning. But it is intriguing, Jarvis no tes, "that an ancient gene like FoxP2 appears to have something to do with learned vocalizations both in humans and in birds." --Sarah Graham
� 1996-2004 Scientific American, Inc. All rights reserved. ----		News June 03, 2003   Vocal Learning Similar in Humans, Birds A baby songbird doesn't emerge from the egg singing perfectly. It starts out babbling and gradually refines its tune over time. Human infants follow a similar developmental path when learning to talk. Scientists have thus often compared the acquisition of human speech to that of birdsong. But whether the mechanisms of vocal development are the same in humans and birds is a question few studies have tackled. To that end, new research should prove insightful. According to a report published online this week by the Proceedings of the National Academy of Sciences, babbling human babies respond to social cues from their mothers in much the way that avian babies do. Previous efforts to understand how babies learn to talk had focused on the role of imitation in speech acquisition. In the new work, psychologist Michael H. Goldstein of Franklin and Marshall College and his colleagues turned their attention to social interactions between eight-month-old infants and their mothers. The researchers directed the mothers to act in certain ways while responding to their baby's utterances during 30-minute play sessions. "The mothers did not change how they talked but whether they touched or smiled at the baby," team member Meredith West of Indiana University explains. Like songbird chicks, the investigators found, the babies registered the social consequences of sound-making and adjusted their babbling accordingly. West describes the findings as the first to show "that babies change how they vocalize in response to social responses--not sounds, but sights--by using more mature sounds." Remarks Goldstein: "This project shows that maternal behavior and infant sensory capacities interact to generate the development of more advanced infant behavior. It shows that social learning is a crucial part of vocal development." --Kate Wong
� 1996-2004 Scientific American, Inc. All rights reserved. ----

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