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Category: Evolution (page 2 of 4)

03.15.2013

is the paleo diet scientific?

The paleo diet recommends eating a diet rich in meats, seafood, vegetables, fruits, and nuts while avoiding refined grains and sugars. The thinking is that the human body is best served on a diet that mimics what hunter-gatherers ate. Laura Miller argues that the diet is not scientific in Salon:

For this reason, generalizations about the typical hunter-gatherer lifestyle are spurious; it doesn’t exist. With respect to what people ate (especially how much meat), the only safe assumption was “whatever they could get,” something that to this day varies greatly depending on where they live. Recently, researchers discovered evidence that people in Europe were grinding and cooking grain (a paleo-diet bugaboo) as far back as 30,000 years ago, even if they weren’t actually cultivating it. “A strong body of evidence,” Zuk writes, “points to many changes in our genome since humans spread across the planet and developed agriculture, making it difficult at best to point to a single way of eating to which we were, and remain, best suited.”…

Furthermore, the fossil record of the Stone Age is so small and necessarily incomplete that its ability to tell us about paleolithic society is severely limited. Consider this: For all we know, the first tools were not stone implements but woven slings designed to allow a mother to carry an infant while foraging; it’s just that stone happens to survive longer than fibers.

01.24.2013

dogs, wolves and carbs

Domesticated dog breeds evolved long ago from the wolf. In a study published in Nature, researchers examined differences in the genomes of modern domesticated breeds and wolves and made some interesting discoveries. They expected differences in the nervous systems since the species behave differently. They also found many differences in genes effecting metabolism, especially digestion of carbohydrates. Domesticated breeds digest starches much better than wolves.  From Science News:

The new study focuses on genetic differences between 60 dogs representing 14 breeds and 12 wolves from around the world. Those changes, the researchers reasoned, could identify genes that were important in separating dogs from wolves.

The researchers determined the genetic makeup of groups of dogs and compared the results to those from wolves, concentrating on parts of the genetic instruction book that differ between the two species. As they had expected, the researchers uncovered differences in many genes relating to the brain. But the search also revealed lots of genes involved in starch digestion and metabolism, and in the use of fats. Dogs, the team found, have more copies than wolves do of the AMY2B gene, which produces an enzyme that breaks starch into easily digestible sugars.

Other genetic variants seem to contribute to dogs’ increased ability to convert a sugar called maltose to glucose, the sugar that cells prefer to burn for energy. Yet other genetic changes improve dogs’ ability to move glucose into their cells. Combined, the tweaks alter dogs’ metabolism so they can get more energy out of a carbohydrate-rich diet than wolves can, the researchers conclude. The scientists confirmed the effect of the genetic variants by identifying biochemical differences in starch metabolism in blood and tissue samples from dogs and wolves.

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.

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