jueves, 26 de octubre de 2006

Study Suggests Evolutionary Link Between Diet, Brain Size In Orangutans

In a study of orangutans living on the Indonesian islands of Borneo and Sumatra, scientists from Duke University and the University of Zurich have found what they say is the first demonstration in primates of an evolutionary connection between available food supplies and brain size.

Andrea Taylor deduced brain size by measuring orangutan skulls. (Photo Credit: Megan Morr / Courtesy of Duke University)

Based on their comparative study, the scientists say orangutans confined to part of Borneo where food supplies are frequently depleted may have evolved through the process of natural selection comparatively smaller brains than orangs inhabiting the more bounteous Sumatra.

The findings "suggest that temporary, unavoidable food scarcity may select for a decrease in brain size, perhaps accompanied by only small or subtle decreases in body size," said Andrea Taylor and Carel van Schaik in a report now online in the Journal of Human Evolution.

Taylor is an assistant professor at Duke's departments of Biological Anthropology and Anatomy and of Community and Family Medicine. Van Schaik directs the University of Zurich's Anthropological Institute & Museum, and he also is an adjunct professor of biological anthropology and anatomy at Duke, where he had worked for 15 years.

"To our knowledge, this is the first such study to demonstrate a relationship between relative brain size and resource quality at this microevolutionary level in primates," they said.

Such a change would provide support for what Taylor called the "expensive tissue" hypothesis. "Compared to other tissues, brain tissue is metabolically expensive to grow and maintain," she said. "If there has to be a trade-off, brain tissue may have to give."

"The study suggests that animals facing periods of uncontrollable food scarcity may deal with that by reducing their energy requirement for one of the most expensive organs in their bodies: the brain," van Schaik added.

"This brings us closer to a good ecological theory of variation in brain size, and thus of the conditions steering cognitive evolution," he said. "Such a theory is vital for understanding what happened during human evolution, where, relative to our ancestors, our lineage underwent a threefold expansion of brain size in a few million years."

In their study, Taylor and van Schaik focused on several varieties of orangutans, an endangered primate closely related to humans.

Members of the orang species inhabiting Sumatra, called Pongo abelii, live in the island's most favored environment, where soils are best for growing the fruits they most like to eat. "They'll eat fruits as often as they can, and they'll travel farther away for them if not nearby," Taylor said.

Sumatra also appears to be less subject to periodic "El Niño" climatic fluctuations that disrupt vegetative growth on other islands in the Indonesian region, the researchers' report said.

The scientists found that the nutritionally well-off Sumatran orangutans differed most strikingly from Pongo pygmaeus morio, one of the three subspecies occupying the island of Borneo. The morio subspecies lives in the northeastern part of the island where soils are poorer, access to fruit is most iffy and the impact of El Niño events can be significant.

Those factors "converge to produce an environment for orangutans of eastern Borneo that is at times seriously resource-limited," the scientists wrote. During extensive fruit-short periods, the animals have to "resort to fallback foods with reduced energy and protein content, such as vegetation and bark," they added.

In previous studies, reported in the April 2006 issue of the Journal of Human Evolution, Taylor found evidence that orangs living in Borneo's northeast have jaws that are better able to handle tougher varieties of food than orangutans in other parts of Borneo or Sumatra.

This improved feeding efficiency, coupled with a relatively small brain, would enable such animals to adapt to their conditions by both maximizing their resources and conserving energy, she said.

In addition, studies by van Schaik and other scientists have suggested that Borneo's morio orangs bear offspring more frequently than do Sumatra's orangs. Such relatively short intervals between births could themselves be tied to smaller brains in such higher primates as orangutans, van Schaik and Taylor wrote in their current report.

"Larger-brained apes have slower-paced life histories," they said. "Assuming selection is acting on brain size, life history is prolonged because development of larger brains require more time."

Their previous work led Taylor, an anatomist who studies bones, to begin collaborating with van Schaik, a field biologist who studies living orangs in the wilds, to address the question of whether nutrition, brain size and interbirth intervals might be linked.

Other scientists working in the 1980s had found no differences in brain size among orangs from Borneo and Sumatra, Taylor said. But that work sampled animals only from west Borneo and not from resource-limited east Borneo, she added.

In their own studies, as well as in studies by other researchers, "we see greater anatomical differences amongst the Bornean populations than we see between the Bornean and Sumatran populations," Taylor said.

In addition to having physical differences, Bornean orangs also inhabit areas that vary more ecologically than do comparative orangutan habitats on Sumatra. "The eastern parts of Borneo suffer more from El Niño-related droughts than parts of western Borneo," the scientists wrote. "The effects of El Niño on tropical rain forest composition and diversity are also more marked in eastern compared to western parts."

So Taylor and van Schaik undertook "a comprehensive re-evaluation of brain size among all orangutan species and subspecies," they wrote.

Since they couldn't measure brain size in wild, living members of these endangered animals, Taylor sought out skulls from museums and other sources. In all, they compared 226 adult specimens from the four distinct populations occupying Sumatra and Borneo.

Among these populations, orangutans of the Pongo pygmaeus morio species on Borneo "consistently exhibit the absolutely and relatively smallest cranial capacity," the researchers concluded. Although the researchers found reduced brain sizes in both male and female orangutans, the differences within the small group of animals studied were statistically significant only for the females, they noted.

As to what may cause the gender difference, the researchers note that female morio are notably smaller than their male counterparts and that they generally are at greater risk for nutritional stress because of pregnancy and lactation and their smaller homes ranges.

"The general scenario supported by these results, then, is that an increase in the frequency of uncontrollable periods of low energy intake in one part of the orangutan's geographic range selected for a reduction in brain size," the researchers said.

Similar evolutionary pressures within resource-poor environments also may explain the smaller-than-normal brain size of a controversial 18,000-year-old skull recently found on the Indonesian island of Flores, Taylor and van Schaik said in their article.

In announcing the find in 2004, the skull's discoverers suggested that the small-brained specimen represented a new dwarf early human species that somehow survived until fairly recently. Critics argue that it actually is a modern human afflicted with microcephaly, a genetic disorder characterized by an abnormally small head and an underdeveloped brain.

Web address: http://www.sciencedaily.com/releases/2006/10/061023192505.htm

martes, 24 de octubre de 2006

La primera migración

  1. Una paleontóloga de Cambridge propone que los 'Homo sapiens' modernos poblaron la Tierra en dos oleadas
  2. Los aborígenes australianos son la herencia de la más antigua


Hace 70.000 años, unas tribus de Homo sapiens dejaron su cuna africana y se lanzaron a la colonización del mundo: partiendo de la actual Eritrea, cruzaron el estrecho de Bab el Mandeb, alcanzaron la península Arábiga y, con el paso de las generaciones, bordeando las costas o saltando de isla en isla, hollaron la lejana Australia hace 60.000 años. Los primeros emigrantes modernos llegaron ciertamente lejos, pues cubrieron 12.000 kilómetros, pero su éxito demográfico fue más bien escaso: la herencia genética de aquellas poblaciones solo es detectable hoy en día en unos cuantos miles de personas en Australia y en recónditos rincones de Asia oriental y el Índico.
No hay más herencia visible. Lo dice la genética: o se extinguieron o fueron asimilados sin dejar rastro, puesto que todo el resto del mundo, incluyendo el resto de África, desciende de una segunda expansión mucho más exitosa que aconteció hace 50.000 años. Esto es al menos lo que propone
Marta Mirazón Lahr, paleoantropóloga de la Universidad de Cambridge (Reino Unido), para quien las dos migraciones son la única forma de explicar las particularidades de los nativos australianos. Mirazón participó en un congreso en Barcelona invitada por el programa de ciencia de la Obra Social La Caixa.

"Es cierto que los estudios genéticos apuntan hacia una única migración porque todos los humanos somos muy parecidos, pero cuando uno estudia la morfología y las herramientas de los antiguos australianos se da cuenta de que algo no encaja", afirma.

Avance del desierto

Una crisis climática que desertizó el África tropical fue posiblemente el acicate que hace 70.000 años amplió los horizontes del Homo sapiens. Eso sí, fueron muy pocos, "quizá 500 o 1.000", los que realmente cruzaron Bab el Mandeb. Los colonizadores, adaptados a una dieta más marinera, siguieron por la costa de lo que hoy es Irán hasta llegar al delta del Indo y la India. Aunque varios estudios lo sugieren, Mirazón no cree que la colonización definitiva del planeta partiera de las poblaciones que se instalaron en esas regiones: "Habría que atravesar desiertos o bien los montes Zagros o el Himalaya. No parece fácil". En cambio, la paleoantropóloga considera que los sapiens de aquella época ya tenían suficiente destreza marinera como para sortear los numerosos estrechos que llevan a Australia, incluyendo uno último de 90 kilómetros de anchura. "Podían fabricar barcazas capaces de transportar a varias familias".
Uno de los escollos de la hipótesis de las dos migraciones es que no se han encontrado restos ni descendientes en la India, territorio por el que forzosamente debieron de pasar aquellos primitivos colonizadores. Mirazón Lahr afirma que la erupción del volcán Toba (Indonesia), la mayor en el último millón de años en la Tierra, pudo abocar a la extinción a las comunidades locales en la India y sepultar cualquier resto arqueológico. En su opinión, no es nada descabellado pensar en grandes extinciones porque la humanidad ha sufrido varios cuellos de botella en los últimos 200.000 años.
La migración de hace 70.000 años no ha dejado huella visible en la India, al menos por ahora, pero en cambio sí hay una indudable herencia en poblaciones actuales de las islas Nicobar y Andamán y en núcleos aislados de Filipinas, Malaisia e Indonesia. "Son tribus que quedaron arrinconadas". Originariamente, estas poblaciones reliquias no eran sustancialmente diferentes al grueso de los humanos modernos, pero el aislamiento acentuó ciertos rasgos, como la baja estatura, dice Mirazón.
¿Las diferencias entre los antepasados de los aborígenes australianos y el resto de la población mundial son debidas a una evolución separada, fruto del aislamiento, o a diferentes orígenes africanos? "No tenemos ni idea del proceso de diferenciación dentro de África que llevó al origen del hombre moderno hace 150.000 años. En líneas generales, los colonizadores de ambas migraciones eran muy parecidos, pero no creo salieran de los mismos linajes", concluye la paleontropóloga.

Fuente: El Periódico de Catalunya, 24-10-2006, www.elperiodico.cat

jueves, 12 de octubre de 2006

DNA trail points to human brain evolution

20061012101452-chimpsect6.jpg 12:01 11 October 2006
NewScientist.com news service
Roxanne Khamsi

The human brain may have evolved beyond that of our primate cousins because our brain cells are better at sticking in place, researchers say.

A new study comparing the genomes of humans, chimps, monkeys and mice found an unexpectedly high degree of genetic difference in the human DNA regions that influence nerve cell adhesion, compared with the DNA of the other animals.

Accelerated evolution here allowed human brain cell connections to form with greater complexity, enabling us to grow bigger brains, the researchers suggest.

The genetic assembly of the ten billion neurons in the human brain relies on precise expression of adhesion molecules that allow for thousands of connections between neurons and the matrix of proteins around them.

“Cell adhesion controls many aspects of brain development” including growth and structure, says Shyam Prabhakar at Lawrence Berkeley National Laboratory in Berkeley, California, US, who carried out the genetic analysis with colleagues.

Tests are now needed to reveal whether levels of proteins involved in nerve adhesion do in fact physically differ between the brains of monkeys, chimps and humans, as suggested by the DNA findings. “We don’t have any [physical] changes to link the genetic changes to,” explains Todd Preuss at Yerkes National Primate Research Center in Atlanta, Georgia, US.

Prabhakar will present the findings at the American Society of Human Genetics meeting in New Orleans, US, this week.

martes, 3 de octubre de 2006

¿Qué nos hace diferentes?


La revista "Time" dedica a su tema de portada un interesante artículo sobre qué nos hace diferentes del resto de primates.

Podeis encontrar el artículo en:

Time, October 9, vol.168, no.15. What make us different? By Michael D. Lemonick & Andrea Dorfman


Abstracts de Mona en Folia Primatologica


En el número de junio de 2006 de la prestigiosa revista de la Federación Europea de Primatología, "Folia Primatologica ", se han publicado los abstracts de las dos comunicaciones de Mona que se presentaron en el pasado Congreso de la Asociación Primatológica Española , celebrado en Madrid en 2005. De igual manera, ya están introducidas las referencias en la base de datos de primatología "PrimateLit" (http://primatelit.library.wisc.edu/ ).

Las referencias son las siguientes:

• Feliu, O., y Veà, J. (2006). Use of space in structural preferences by a group of humanized chimpanzees (Pan troglodytes troglodytes). Folia Primatologica, 77(4), 311.

• Mosquera, M., Llorente, M., Riba, D., y Feliu, O. (2006). Hand laterality in humanized chimpanzees (Pan troglodytes). Folia Primatologica, 77(4), 323.

Aquellas personas que estéis interesados en obtener los documentos no dudéis en poneros en contacto con Miquel Llorente: mllorente@fmrecerca.org

IPHES y MONA en el XI Congreso Nacional y VIII Iberoamericano de Etología

Los pósters que hemos presentado en el XI Congreso Nacional y VIII Iberoamericano de Etología , celebrado en Puerto de la Cruz, Tenerife, del 19 al 22 de septiembre, han tenido un gran éxito en la sesión de comunicaciones en panel. El interés del público y asistentes al congreso hacia los pósters presentados ha sido muy alto y superior al resto, cosa que nos enorgullece teniendo en cuenta el alto nivel de este tipo de reuniones científicas que organiza la Sociedad Española de Etología , y al que están acudiendo etólogos de España, Ibero América, EEUU y Europa.

Os recuerdo que las comunicaciones en panel presentadas eran las siguientes:

* Arós García, L., Llorente Espino, M., Pazos Ruiz, A. B., y Feliu Olleta, O. (2006a). Comportamiento postural en un grupo de chimpancés (Pan troglodytes) en semicautividad. Diferencias entre edades. Comunicación presentada en XI Congreso Nacional y VIII Iberoamericano de Etología, Puerto de la Cruz, Tenerife.

* Arós García, L., Llorente Espino, M., Pazos Ruiz, A. B., y Feliu Olleta, O. (2006b). Evaluación de los comportamientos asociados a la postura bípeda en chimpancés (Pan troglodytes). Comunicación presentada en XI Congreso Nacional y VIII Iberoamericano de Etología, Puerto de la Cruz, Tenerife.

* Llorente Espino, M., y Arós García, L. (2006). Análisis secuencial de un proceso de adopción en chimpancés (Pan troglodytes). Comunicación presentada en XI Congreso Nacional y
VIII Iberoamericano de Etología, Puerto de la Cruz, Tenerife.

Para más información podéis poneros en contacto con Miquel Llorente: mllorente@fmrecerca.org
Foto: Leonor Arós junto a uno de los pósters presentados en Tenerife.

Publicado artículo en LATERALITY


El pasado 28 de agostó se publicó online en la prestigiosa revista "Laterality: Asymmetries of Body, Brain and Cognition " un artículo sobre la investigación llevada a cabo en Fundación Mona sobra lateralización manual y especialización hemisférica en chimpancés.

Este proyecto de investigación fue llevado a cabo conjuntamente por miembros del IPHES , Fundación Mona, URV y el Centro UCM-ISCII de Evolución y Comportamiento Humanos.

En los próximos meses saldrá publicado en la edición en papel de la revista británica, editada por Psychology Press.

Adjunto la referencia y el abstract del artículo:

Mosquera, M., Llorente, M., Riba, D., Estebaranz, F., Gonzalez, M., Lorenzo, C., Sanmart, N., Toll, M., Carbonell, E., & Feliu, O. (2006). Ethological study of manual laterality in naturalistic housed chimpanzees (Pan troglodytes) from the Mona Foundation Sanctuary (Girona, Spain). Laterality, in press.


Ethological study of manual laterality in naturalistic housed chimpanzees (Pan troglodytes) from the Mona Foundation Sanctuary (Girona, Spain).


Marina Mosquera1, Miquel Llorente2,3, David Riba1, Ferran Estebaranz3, Mar González-Brao3, Carlos Lorenzo1,4, Neus Sanmartí3, Macarena Toll3, Eudald Carbonell1,2 y Olga Feliu3.


1 Universitat Rovira i Virgili, Tarragona, Spain

2 Institut Català de Paleoecologia Humana i Evolució Social (IPHES), Tarragona, Spain

3 Unitat de Recerca i Laboratori d’Etologia, Fundació Mona, Girona, Spain

4 Centro UCM-ISCIII de Evolución y Comportamiento Humanos, Madrid, Spain


Laterality, (in press).

Publicado online el 28 de agosto de 2006 (http://www.tandf.co.uk/journals/titles/1357650X.asp).

DOI: 10.1080/13576500600886754

Print ISSN: 1357-650X

Online ISSN: 1464-0678


During recent years, handedness of nonhuman primates has been the subject of several studies, especially focused on our closest relatives: the chimpanzees. These studies have dealt with both wild and captive chimpanzees, and they seem to point to divergent conclusions, which have been interpreted as a by-product of the human influence in the captive samples. Here we present the results of a study of 10 chimpanzees (Pan troglodytes). In the past, they were trained in circus and marketing tasks (humanised behaviours), until they were confiscated and accepted into the Mona Foundation (in northeast Spain) in 2000, where they live in a semi-naturalistic environment. This study has been performed through observational bouts without systematic human influence, recording the actions carried out by chimpanzees when performing spontaneous activities. Our results indicate that chimpanzees that were under strong human influence in the past show the same trend in handedness as those living in freedom: few significant lateralities were observed among either individuals or tasks. So, laterality may not be influenced by humanisation. However, this conclusion must be taken as preliminary because very few individuals were studied.


Miquel Llorente

Correo electrónico: mllorente@fmrecerca.org