riecroonerza.tk In addition to skin tone variation, the scientists also noted a wide variation in eye colour among Latin Americans. But we show that eye colour is a broad continuum, and by studying the subtler variation within brown to black, we found two new genes linked to it", said Dr Anood Sohail University of Cambridge. The study's findings help explain the variation of skin, hair and eye colour of Latin Americans, shed light on human evolution, and inform an understanding of the genetic risk factors for conditions such as skin cancer.
Materials provided by University College London. Note: Content may be edited for style and length. Science News. Nature Communications , ; 10 1 DOI: ScienceDaily, 21 January University College London.
Genetic study provides novel insights into the evolution of skin color. Retrieved September 27, from www.
The findings help explain the vast range of skin color on the African His observations:. It is impossible to escape the impression that the duped monkey had acquired knowledge, and that as he reached for the cup he had an expectation or belief about what he would find underneath. His shriek reflected his outrage at this egregious betrayal of expectation.
Many years later, Ruth Colwill and Robert Rescorla carried out a more controlled version of the same experiment. They began by training rats to make two responses, pressing a lever and pulling a chain. When the rats pressed the lever they received a small food pellet; when they pulled the chain they received liquid sucrose. By the behaviorist view, the rats had learned only to press the lever or pull the chain whenever they saw them.
By the cognitive view, the rats had formed some kind of mental representation of the relation between a particular act and a specific type of food. To test between these hypotheses, Colwill and Rescorla made either the food pellet or the water unpalatable by adding lithium chloride, a substance that makes rats sick. If the rats had learned which food type was associated with which behavioral act, then those for whom the food pellet had been devalued would avoid the lever but continue to pull the chain, whereas those for whom the water had been devalued would do the opposite.
This is exactly what happened.
Through learning, animals acquire information about objects, events, and the relation between them. Their knowledge has content, and this content can be studied scientifically. This conclusion from the laboratory is important, because it encourages us to believe that Darwin was right: we can trace the causation of thought in different species, study its structure, and reconstruct its evolution. But while the scientific study of mind is an exciting prospect, a large dose of humility is in order.
For all of their failings, the behaviorists did understand that, whereas behavior can be unambiguously observed and measured, knowledge and the content of mental states are abstract, hard to measure, and difficult even to define. When we claim that a rat has formed an association between bar pressing and a particular type of food, what exactly is the nature of its knowledge? Does the rat think that the bar somehow stands for that food? Does it believe that pressing the bar causes the food to appear? Can rats distinguish between the relations A represents B and A causes B?
None of these questions is easy to answer. On first—and perhaps even further—inspection, baboons might seem less than ideal subjects for a study of the mind. Among other failings, they are not as closely related to humans as some other nonhuman primates.
Baboons are members of the genus Papio, Old World monkeys that shared a common ancestor with humans roughly 30 million years ago. Baboons are more closely related to humans than monkeys of the New World, but they are much less closely related than the African apes—especially chimpanzees Pan troglodytes —which diverged from our own ancestors roughly five to seven million years ago.
Moreover, the conservation status of baboons confers neither glamour nor prestige on those who study them. They flourish throughout the continent, occupying every ecological niche except the Sahara and tropical rain forests. They are quick to exploit campsites and farms and are widely regarded as aggressive, destructive, crop-raiding hooligans.
Finally, baboons are not particularly good-looking—many other monkeys are far more photogenic. Indeed, through the ages baboons have evoked as much if not more repulsion than admiration. Baboons are interesting, however, from a social perspective. Their groups number up to individuals and are therefore considerably larger than most chimpanzee communities. Each animal maintains a complex network of social relationships with relatives and nonrelatives—relationships that are simultaneously cooperative and competitive.
Navigating through this network would seem to require sophisticated social knowledge and skills. Moreover, the challenges that baboons confront are not just social but also ecological. Food must be found and defended, predators evaded and sometimes attacked. They also allow us to study social cognition in the absence of human training, in the social and ecological contexts in which it evolved. Traits arise or are maintained because they help the individuals who possess them to solve a problem, thereby giving those individuals an advantage over others in survival and reproduction.
A blunt, heavy beak allows a finch to crush hard, dry seeds and survive a withering dry season; antlers enable a stag to defeat his rivals and mate with more females. To understand the evolution of a trait, therefore, we need to understand how it works, and what it allows an individual to do that might otherwise be impossible. And brains, Darwin realized, were biological traits like any other.
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To understand how they evolved, we must understand the problems they were designed to solve. In recent years, studies of the brain, intelligence, and evolution in animals have produced two general conclusions that will guide our study of baboon metaphysics. First, natural selection often creates brains that are highly specialized. Yet despite these specialized skills, there is no evidence that terns, ants, bees, or nutcrackers are generally more intelligent than other species.
Specialized intelligence may be widespread in animals because brain tissue is costly to develop and maintain. The human brain uses energy at a rate comparable to that used by the leg muscles of a marathon runner when running. If brain tissue is energetically expensive, the cheapest way to evolve a specialized skill may be through a small number of especially dedicated brain cells rather than a larger, general-purpose brain.
For arctic terns, the ability to fly from pole to pole in the spring and fall is adaptive because it allows the birds to live in perpetual summer. But it has done so in the cheapest, most energy-efficient way possible—by selecting specifically for navigational skills. The second general conclusion to emerge from recent research is that the domain of expertise for baboons—and indeed for all monkeys and apes—is social life.
Most baboons live in multimale, multifemale groups that typically include eight or nine matrilineal families, a linear dominance hierarchy of males that changes often, and a linear hierarchy of females and their offspring that can be stable for generations. Daily life in a baboon group includes small-scale alliances that may involve only three individuals and occasional large-scale, familial battles that involve all of the members of three or four matrilines.
Males and females can form short-term bonds that lead to reproduction, or longer-term friendships that lead to cooperative child rearing. We now have examples of two genetic groups of people who were adapting to this very harsh landscape. The genetic analysis points towards a divergence of all ancient Native Americans from a single east Asian source population somewhere between 36, to 25, years ago—well before humans crossed into Beringia, an area that includes the land bridge connecting Siberia and Alaska at the end of the last ice age.
That means that somewhere along the way, either in eastern Asia or in Beringia itself, a group of people became isolated from other east Asians for about 10, years, long enough to become a unique strain of humanity.
But since humans in North America are not reliably documented before 14, years ago, how and where these two groups could have been separated long enough to become genetically distinct is still unclear. The first is that the two groups became isolated while still in east Asia, and that they crossed the land bridge separately—perhaps at different times, or using different routes. A second theory is that a single group moved out of Asia, then split into Beringians and ancient Native Americans once in Beringia.
The Beringians lingered in the west and interior of Alaska, while the ancestors of modern Native Americans continued on south some time around 15, years ago. John Hoffecker , who studies the paleoecology of Beringia at the University of Colorado-Boulder, says there is still plenty of room for debate about the geographic locations of the ancestral splits.
But the new study fits well with where the thinking has been heading for the last decade, he adds. However, that same diversity—revealed through research on Native American cranial morphology and tooth structure —creates its own dilemma.