La importancia de la extinción de los dinosaurios para la evolución cerebral de los mamíferos

El Ser Humano es considerablemente más corpulento que casi todos sus ancestros. Según algunas estimaciones, los padres de los tatarabuelos de bastantes personas actuales eran como promedio unos 10 centímetros más bajos que éstas.

Yendo mucho más atrás en el tiempo, la diferencia aumenta de modo impresionante. Los ancestros del Ser Humano y de los mamíferos modernos en general, que vivieron hace unos 80 millones de años, pesaban menos de 100 gramos y por lo general medían sólo unos pocos centímetros. Los nichos ecológicos que les habrían permitido tener un cuerpo más grande estaban ocupados por los dinosaurios. Sólo la gran extinción que acabó con los dinosaurios hace 65 millones de años permitió que nuestros ancestros experimentasen un espectacular aumento de tamaño. En sólo unos pocos millones de años, los mamíferos pasaron a ser más de 100 veces más grandes que sus ancestros del Mesozoico.

Un equipo internacional de investigadores dirigido por científicos del Instituto Max Planck para la Dinámica y la Autoorganización, la Universidad de Gotinga, la Universidad Goethe en Fráncfort y el Centro Bernstein en Gotinga, en Alemania todas estas instituciones, ha llegado a la conclusión de que este crecimiento acelerado probablemente condujo a un "rediseño" fundamental de circuitos neuronales en el cerebro, y ha aclarado algunos detalles al respecto.

Tal como descubrió el equipo de Wolfgang Keil y Fred Wolf, los circuitos neuronales en la corteza visual del cerebro, correspondientes a los detalles más pequeños, evolucionaron de forma independiente en linajes diferentes. Las simulaciones por ordenador y los cálculos matemáticos muestran que esta correspondencia refleja leyes básicas de la autoorganización de redes neuronales de gran escala. Los investigadores señalan la existencia de "fósiles vivientes del desarrollo del cerebro". Estos son especies que han conservado hasta la actualidad la arquitectura de los circuitos neuronales de nuestros ancestros evolutivos. Entre ellos, sorprendentemente, está también uno de los parientes más cercanos de los primates: el ratón.

Ancestro, a la izquierda, y descendiente, a la derecha. (Foto: © MPIDS)

Un aspecto esencial de la evolución humana fue el aumento del tamaño del cerebro, y especialmente de la corteza cerebral, cuyas funciones incluyen la percepción consciente, la toma de decisiones, y muchos de procesos de la memoria. En el Ser Humano, así como en muchos otros mamíferos, esta región cerebral está dividida en módulos en los que grupos de neuronas están interconectadas conformando redes densas y contribuyen a realizar tareas comunes, como por ejemplo la percepción de un color determinado.

Biology: Research blurs line between human and animal Monkeys do math, baboons seem to read, orangutans do planning

By SETH BORENSTEINASSOCIATED PRESS
WASHINGTON — The more we study animals, the less special we seem.
Baboons can distinguish between written words and gibberish. Monkeys seem to be able to do multiplication. Apes can delay instant gratification longer than a human child can. They plan ahead. They make war and peace. They show empathy. They share.
“It’s not a question of whether they think — it’s how they think,” says Duke University scientist Brian Hare.
Now scientists wonder if apes are capable of thinking about what other apes are thinking.
The evidence that animals are more intelligent and more social than we thought seems to grow each year, especially when it comes to primates. It’s an increasingly hot scientific field with the number of ape and monkey cognition studies doubling in recent years, often with better technology and neuroscience paving the way to unusual discoveries.
This month scientists mapping the DNA of the bonobo ape found that, like the chimp, bonobos are only 1.3 per cent different from humans.
Says Josep Call, director of the primate research centre at the Max Planck Institute in Germany: “Every year we discover things that we thought they could not do.”
Call says one of his recent more surprising studies showed that apes can set goals and follow through with them.
Orangutans and bonobos in a zoo were offered eight possible tools — two of which would help them get at some food. At times when they chose the proper tool, researchers moved the apes to a different area before they could get the food, and then kept them waiting as much as 14 hours. In nearly every case, when the apes realized they were being moved, they took their tool with them so they could use it to get food the next day, remembering that even after sleeping. The goal and series of tasks didn’t leave the apes’ minds.
Call says this is similar to a person packing luggage a day before a trip: “For humans it’s such a central ability, it’s so important.”
For a few years, scientists have watched chimpanzees in zoos collect and store rocks as weapons for later use. In May, a study found they even add deception to the mix. They created haystacks to conceal their stash of stones from opponents, just like nations do with bombs.
Hare points to studies where competing chimpanzees enter an arena where one bit of food is hidden from view for only one chimp. The chimp that can see the hidden food, quickly learns that his foe can’t see it and uses that to his advantage, displaying the ability to perceive another ape’s situation. That’s a trait humans develop as toddlers, but something we thought other animals never got, Hare said.
And then there is the amazing monkey memory.
At the National Zoo in Washington, humans who try to match their recall skills with an orangutan’s are humbled. Zoo associate director Don Moore says: “I’ve got a Ph.D., for God’s sake, you would think I could out-think an orang and I can’t.”
In French research, at least two baboons kept memorizing so many pictures — several thousand — that after three years researchers ran out of time before the baboons reached their limit. Researcher Joel Fagot at the French National Center for Scientific Research figured they could memorize at least 10,000 and probably more.

And a chimp in Japan named Ayumu who sees strings of numbers flash on a screen for a split-second regularly beats humans at accurately duplicating the lineup. He’s a YouTube sensation, along with orangutans in a Miami zoo that use iPads.
It’s not just primates that demonstrate surprising abilities.
Dolphins, whose brains are 25 per cent heavier than humans, recognize themselves in a mirror. So do elephants. A study in June finds that black bears can do primitive counting, something even pigeons have done, by putting two dots before five, or 10 before 20 in one experiment.
The trend in research is to identify some new thinking skill that chimps can do, revealing that certain abilities are “not uniquely human,” said Emory University primatologist Frans de Waal. Then the scientists find that same ability in other primates further removed from humans genetically. Then they see it in dogs and elephants.
“Capacities that we think in humans are very special and complex are probably not so special and not so complex,” de Waal said. “This research in animals elevates the animals, but it also brings down the humans.... If monkeys can do it and maybe dogs and other animals, maybe it’s not as complex as you think.”
At Duke, professor Elizabeth Brannon shows videos of monkeys that appear to be doing a “fuzzy representation” of multiplication by following the number of dots that go into a box on a computer screen and choosing the right answer to come out of the box. This is after they’ve already done addition and subtraction.
This spring in France, researchers showed that six baboons could distinguish between fake and real four-letter words — BRRU vs. KITE, for example. And they chose to do these computer-based exercises of their own free will, either for fun or a snack.
It was once thought the control of emotions and the ability to empathize and socialize separated us from our primate cousins. But chimps console, and fight, each other. They also try to soothe an upset companion, grooming and putting their arms around him.
“I see plenty of empathy in my chimpanzees,” de Waal said. But studies have shown they also go to war against neighbouring colonies, killing the males and taking the females. That’s something that also is very human and led people to believe that war-making must go back in our lineage six million years, de Waal said.
When scientists look at our other closest relative, the bonobo, they see a difference. Bonobos don’t kill. Hare says his experiments show bonobos give food to newcomer bonobos, even when they could choose to keep all the food themselves.
One reason scientists are learning more about animal intellect is computers, including touch screens. In some cases, scientists are setting up banks of computers available to primates 24-7. In the French word recognition experiment, Fagot found he got more and better data when it was the baboons’ choice to work.

Animal cognition researcher Steve Ross at the Lincoln Park Zoo in Chicago agrees.
“The apes in our case seem to be working better when they have that control, that choice to perform,” he said.
Brain scans on monkeys and apes also have helped correct mistaken views about ape brain power. It was once thought the prefrontal cortex, the area in charge of higher reasoning, was disproportionately larger than the rest of the brain only in humans, giving us a cognitive advantage, Hare said. But imaging shows that monkey and ape prefrontal cortexes have that same larger scale, he said.
What’s different is that the human communication system in the prefrontal cortex is more complex, Hare said.
So there are limits to what non-human primates can do. Animals don’t have the ability to communicate with the complexity of human language. In the French study, the baboons can recognize that the letters KITE make a word because through trial and error they learn which letters tend to go together in what order. But the baboons don’t have a clue of what KITE means. It’s that gap that’s key.
“The boundaries are not as sharp as people think, but there are certain things you can’t overcome and language is one of them,” said Columbia University animal cognition researcher Herbert Terrace.
And that leads to another difference, Ross said. Because apes lack language skills, they learn by watching and mimicking. Humans teach with language and explanation, which is faster and better, Ross said.
Some of the shifts in scientific understanding of animals are leading to ethical debates. When Emory University researcher Lori Marino in 2001 co-wrote a groundbreaking study on dolphins recognizing themselves in mirrors, proving they have a sense of self similar to humans, she had a revelation.
“The more you learn about them, the more you realize that they do have the capacity and characteristics that we think of as a person,” Marino said. “I think it’s impossible to ignore the ethical implications of these kinds of findings.”
After the two dolphins she studied died when transferred to another aquarium, she decided never to work on captive dolphins again. She then became a science adviser to the Nonhuman Rights Project, which seeks legal rights or status for animals. The idea, Marino said, is to get animals such as dolphins “to be deemed a person, not property.”
The intelligence of primates was one of the factors behind a report last year by the Institute of Medicine that said the U.S. National Institutes of Health should reduce dramatically the number of chimpanzees it uses in biomedical research.
The NIH is working on guidelines that would further limit federal medical chimpanzee use down from its current few dozen chimps at any given time, said NIH program planning chief James Anderson. Chimps are a special case, with their use “very, very limited,” he said. But he raises the question: “What happens if your child is sick or your mother is dying” and animal research might lead to a cure?

The issue is more about animal welfare and giving them the right “not to be killed, not to be tortured, not to be confined unnecessarily” than giving them legal standing, said David DeGrazia, a philosophy and ethics professor at George Washington University.
Hare says that focusing on animal rights ignores the problem of treatment of chimps in research settings. He contends that for behavioural studies and even for many medical research tests they could be kept in zoos or sanctuaries rather than labs.
Animals performing tasks in near-natural habitats “is like an Ivy League college” for the apes, Hare said. “We’re going to see them do stunning and sophisticated things.”
DOLPHINS UNDERSTAND ZERO, ELEPHANTS RESCUE EACH OTHER
WASHINGTON — It’s not just man’s closer primate relatives that exhibit brain power. Dolphins, dogs and elephants are teaching us a few lessons, too.
Dolphin brains involve completely different wiring from primates, especially in the neocortex, which is central to higher functions such as reasoning and conscious thought.
Dolphins are so distantly related to humans that it’s been 95 million years since we had even a remotely common ancestor. Yet when it comes to intelligence, social behaviour and communications, some researchers say dolphins come as close to humans as our ape and monkey cousins.
Maybe closer.
“They understand concepts like zero, abstract concepts. They do everything that chimpanzees do and bonobos can do,” said Lori Marino, a neuroscientist at Emory University who specializes in dolphin research. “The fact is that they are so different from us and so much like us at the same time.”
In recent years, animal researchers have found that thought processes in critters aren’t a matter of how closely related they are to humans. You don’t have to be a primate to be smart.
Dolphin brains look nothing like human brains, Marino said. Yet, she says, “the more you learn about them, the more you realize that they do have the capacity and characteristics that we think of when we think of a person.”
These mammals recognize themselves in the mirror and have a sense of social identity. They not only know who they are, but they also have a sense of who, where and what their groups are. They interact and comprehend the health and feelings of other dolphins so fast it as if they are online with each other, Marino said.
Animal intelligence “is not a linear thing,” said Duke University researcher Brian Hare, who studies bonobos, which are one of man’s closest relatives, and dogs, which are not.
“Think of it like a toolbox,” he said. “Some species have an amazing hammer. Some species have an amazing screwdriver.”
For dogs, a primary tool is their obsessive observation of humans and ability to understand human communication, Hare said. For example, dogs follow human pointing so well that they understand it whether it’s done with a hand or a foot; chimps don’t, said Hare, whose upcoming book is called “The Genius of Dogs.”

Then there are elephants.
They empathize, they help each other, they work together. In a classic co-operation game, in which animals only get food if two animals pull opposite ends of a rope at the same time, elephants learned to do that much quicker than chimps, said researcher Josh Plotnik, head of elephant research at the Golden Triangle Asian Elephant Foundation in Thailand.
They do even better than monkeys at empathy and rescue, said Plotnik. In the wild, he has seen elephants stop and work together to rescue another elephant that fell in a pit.
“There is something in the environment, in the evolution of this species that is unique,” he says.

© Copyright (c) The Vancouver Sun

El enigma de los diez mil individuos que formaban la humanidad de hace cien mil años

Muchos indicios apuntan a que hace unos 100.000 años, la evolución humana experimentó un misterioso "cuello de botella": Al parecer, la población humana de aquella época se redujo hasta llegar a ser de sólo entre 5.000 y 10.000 individuos, que vivían en África.

Sin embargo, con el paso del tiempo, de esta población surgirían humanos con "conducta moderna", cuyo número y área de distribución geográfica crecerían de modo considerable, sustituyendo finalmente a todos los demás primos evolutivos con los que coexistieron, como por ejemplo los neandertales.

Aún se desconoce la causa de este cuello de botella, y las explicaciones propuestas van desde mutaciones genéticas perniciosas hasta catástrofes que alteraron el clima, entre ellas una erupción volcánica colosal.

Ahora parece claro que hay que añadir otro posible factor: una gran incidencia de enfermedades infecciosas, que diezmó a la población humana, pero no pudo acabar con los portadores de una rara mutación que les hacía más resistentes a esas enfermedades. Esos supervivientes y sus descendientes acabaron repoblando el mundo.

Un equipo internacional de investigadores, dirigido por científicos de la Escuela de Medicina de la Universidad de California en San Diego, sugiere que la desactivación de dos genes asociados al sistema inmunitario fue la mutación específica que pudo dar a esos ancestros de los humanos modernos una mejor protección contra algunas cepas de bacterias patógenas, incluyendo Escherichia coli K1 y estreptococos del grupo B, principales causantes de septicemia y meningitis en fetos, recién nacidos y niños pequeños humanos.

El equipo del Dr. Ajit Varki, profesor de medicina celular y molecular en la citada universidad, ha descubierto dos genes que no son funcionales en los humanos, pero que sí lo son en los primates emparentados evolutivamente con nosotros. Estos dos genes pudieron constituir un punto débil crucial explotado por patógenos bacterianos, particularmente letales para recién nacidos y niños pequeños. Matar a los más jóvenes puede tener un impacto demográfico importante en la especie humana.

La supervivencia de la especie pudo depender tanto de resistir al patógeno como de eliminar las proteínas de las que éste se valía para derrotar al sistema inmunitario.

En este caso, el equipo de Varki cree que ocurrió esto último.

Trabajando con el Dr. Victor Nizet, profesor de pediatría y farmacia, el grupo de Varki había mostrado previamente que algunos patógenos pueden valerse de ciertos receptores de señales controlados por genes específicos del organismo invadido para alterar las respuestas inmunitarias de éste en favor del microbio.

Bacterias Escherichia coli. (Foto: UCSD)

En el último estudio, los científicos descubrieron que el gen para el receptor Siglec-13 ya no forma parte del genoma humano moderno, aunque permanece intacto y funcional en los chimpancés, los primos evolutivos más estrechamente emparentados con nosotros. El otro gen, el del receptor Siglec-17, todavía es expresado en los humanos, pero está ligeramente modificado, de tal modo que a partir de él se produce una proteína corta e inactiva que de nada sirve a los patógenos invasores.

En un novedoso experimento, los científicos, incluyendo al Dr. Eric D. Green, director del Instituto Nacional estadounidense de Investigación del Genoma Humano, dependiente de los Institutos Nacionales estadounidenses de Salud, "resucitaron" estos "fósiles moleculares" y comprobaron que las proteínas eran reconocidas por cepas patógenas actuales de E. coli y de estreptococos del grupo B.

Aunque es imposible saber exactamente qué ocurrió durante la citada fase crítica de la evolución humana, los investigadores creen que los ancestros de los humanos modernos se vieron diezmados por una gran amenaza patógena hace entre 100.000 y 200.000 años. Sólo los individuos con esa mutación en dos genes sobrevivieron, convirtiéndose así en la exigua pero resistente población de humanos anatómicamente modernos de la que descendemos todas las personas actuales.

Conviene matizar que, tal como reconoce Varki, es probable que el cuello de botella evolutivo experimentado por la humanidad de aquella época fuese el complejo resultado de múltiples factores interactuando unos con otros. Pero el papel de las citadas enfermedades infecciosas seguramente fue un factor importante, acaso el principal.

How You Feel What Another Body Feels Empathy's surprising roots in the sense of touch

By Jakub Limanowski 

When a friend hits her thumb with a hammer, you don't have to put much effort into imagining how this feels. You know it immediately. You will probably tense up, your "Ouch!" may arise even quicker than your friend's, and chances are that you will feel a little pain yourself. Of course, you will then thoughtfully offer consolation and bandages, but your initial reaction seems just about automatic. Why?
Neuroscience now offers you an answer: A recent line of research has demonstrated that seeing other people being touched activates primary sensory areas of your brain, much like experiencing the same touch yourself would do. What these findings suggest is beautiful in its simplicity—that you literally "feel with" others.
There is no denying that the exceptional interpersonal understanding we humans show is by and large a product of our emotional responsiveness. We are automatically affected by other people’s feelings, even without explicit communication. Our involvement is sometimes so powerful that we have to flee it, turning our heads away when we see someone get hurt in a movie. Researchers hold that this capacity emerged long before humans evolved. However, only quite recently has it been given a name: A mere hundred years ago, the word "Empathy"—a combination of the Greek "in" (em-) and "feeling" (pathos)—was coined by the British psychologist E. B. Titchener during his endeavor to translate the German Einfühlungsvermögen ("the ability to feel into").
Despite the lack of a universally agreed-upon definition of empathy, the mechanisms of sharing and understanding another’s experience have always been of scientific and public interest—and particularly so since the introduction of “mirror neurons.” This important discovery was made two decades ago by  Giacomo Rizzolatti and his co-workers at the University of Parma, who were studying motor neuron properties in macaque monkeys. To compensate for the tedious electrophysiological recordings required, the monkey was occasionally given food rewards. During these incidental actions something unexpected happened: When the monkey, remaining perfectly still, saw the food being grasped by an experimenter in a specific way, some of its motor neurons discharged. Remarkably, these neurons normally fired when the monkey itself grasped the food in this way. It was as if the monkey’s brain was directly mirroring the actions it observed. This “neural resonance,” which was later also demonstrated in humans, suggested the existence of a special type of "mirror" neurons that help us understand other people’s actions.
Do you find yourself wondering, now, whether a similar mirror mechanism could have caused your pungent empathic reaction to your friend maltreating herself with a hammer? A group of scientists led by Christian Keysers believed so. The researchers had their participants watch short movie clips of people being touched, while using functional magnetic resonance imaging (fMRI) to record their brain activity. The brain scans revealed that the somatosensory cortex, a complex of brain regions processing touch information, was highly active during the movie presentations—although participants were not being touched at all. As was later confirmed by other studies, this activity strongly resembled the somatosensory response participants showed when they were actually touched in the same way. A recent study by Esther Kuehn and colleagues even found that, during the observation of a human hand being touched, parts of the somatosensory cortex were particularly active when (judging by perspective) the hand clearly belonged to another person.