evolution – Page 2

11.29.2012

eating meat helped our brains evolve

From Christopher Wanjek in the Washington Post:

At the core of this research is the understanding that the modern human brain consumes 20 percent of the body’s energy at rest, twice that of other primates. Meat and cooked foods were needed to provide the necessary calorie boost to feed a growing brain.

One study, published last month in the Proceedings of the National Academy of Sciences, examined the brain size of several primates. For the most part, larger bodies have larger brains across species. Yet humans have exceptionally large, neuron-rich brains for our body size, while gorillas — three times as massive as humans — have smaller brains with one-third the neurons. Why?

The answer, it seems, is the gorillas’ raw, vegan diet (devoid of animal protein), which requires hours upon hours of eating to provide enough calories to support their mass.

Researchers from Brazil, led by Suzana Herculano-Houzel, a neuroscientist at the Federal University of Rio de Janeiro, calculated that adding neurons to the primate brain comes at a fixed cost of approximately six calories per billion neurons.

For gorillas to evolve a humanlike brain, they would need an additional 733 calories a day, which would require two more hours of feeding, the authors wrote. A gorilla already spends as much as 80 percent of the tropics’ 12 hours of daylight eating.

Tell your vegetarian friends to chew on that.

11.27.2012

tracing the origins of chickens

Photograph of a chicken. Image from PLOS via Scienceblogs

Researchers are interested in tracking down the genetic origins of today’s domesticated chickens. From Science:

Their genes, and those of other isolated populations, are now being sequenced (see sidebar, p. 1022) as part of a larger effort to understand the world’s most common bird and biggest source of animal protein. In 2009, Americans ate 36 billion pounds of chicken, and the numbers keep growing, especially in developing countries in Asia and Africa. That importance is highlighted by the fact that the chicken was the first farm animal to have its genome published, back in 2004. Since then, the proliferation of factory farms, mass bird deaths from avian influenza, and dwindling diversity in chickens have raised concerns about this critical source of food.

A key thrust of research in the past decade has been to track the genetic changes that turned a remarkably shy creature into today’s meat-and-eggs dynamo, with an eye to protecting and improving breeds. But this research has also given scientists the opportunity to unravel a long-standing mystery that fascinated Charles Darwin: Where, when, and how was the chicken domesticated?…

The advent of sequencing tools in the 1990s promised a new line of evidence that went beyond physical characteristics. The results, however, have only heightened the controversy. A draft of the chicken genome, for example, isn’t enough to trace the bird’s evolution: Researchers need ancestral birds for comparison. Geneticists first used mitochondrial DNA (mtDNA) to trace the female line of the species back to its origin. Akishinomiya Fumihito, an ornithologist and prince in Japan’s royal family, extracted sections of mtDNA from Thai red jungle fowl and asserted in a 1994 paper that the findings suggested a single domestication in Thailand. Eight years later, another team used mtDNA from native Chinese chickens to support that idea.

In 2006, however, a team led by Yi-Ping Liu of China’s Kunming Institute of Zoology found nine separate clades—that is, groups descended from a common ancestor—in the mtDNA of a large sample of wild and domestic modern birds. The distribution of the clades suggests a distinct and separate expansion of lineages in southern China, Southeast Asia, and the Indian subcontinent, supporting a multiple origins theory. Another team published a study this week in Heredity based on nuclear DNA, which is not limited to the maternal line, supporting that view.

Much more at the source link. [Subscription may be required.]

10.23.2012

on the origins of blood types

Different antigens are present in A,B, AB and O type blood.

Humans can have blood types A, B, AB or O depending on what type of antigens are present on their red blood cells. A recent study in PNAS determined that these blood types existed in early humans and even in apes and chimps. From Science News:

Different forms of a single blood type gene determine what types of molecules sit on your red blood cells: type A molecules, type B molecules, A and B together, or no intact surface molecules in the case of type O (O was originally called type C, then was changed to O for the German “ohne,” meaning “without”).

The A, B and O versions of the gene differ only slightly, and scientists have debated two scenarios to explain their evolution. One posits that the A version of the gene existed long ago, and the B and/or O versions later cropped up independently in several species (including humans, gorillas, baboons and chimps). Alternatively, all of those species may have inherited the A and B types from a single ancestor.

To get some bloody perspective on the matter, researchers led by Ségurel looked at a particular stretch of DNA in the blood type gene in humans, bonobos, chimpanzees, gorillas, orangutans and several species of monkey. Then the scientists compared that stretch of DNA across species on the larger primate family tree. The pattern they saw suggests that the A and B blood groups were around at least 20 million years ago, well before the chimp-human split, and probably as far back as the common ancestor of humans and old-world monkeys. Sections of DNA in the human A version, for example, more closely matched the A version that gibbons have than the human B version of the gene.

Exactly why evolution would favor a mix of blood types in so many species is a mystery. Depending on blood type, people are more or less susceptible to particular pathogens. Type O people, for example, are more susceptible to cholera and plague, while people with type A are more susceptible to smallpox. Blood group diversity may have been maintained for so long because each version was immunologically advantageous in certain times and places.

GOLLYGEE!

Tag: evolution (page 2 of 4)

eating meat helped our brains evolve

tracing the origins of chickens

on the origins of blood types