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Generally when you think about what separates humans from other species, features like upright walking, large brains and language come to mind.
But diet has actually played an enormous role in human evolution. Today at the annual meeting of the <a href="http://www.aaas.org" target="_blank" rel="noopener">American Association for the Advancement of Science</a>, a panel of anthropologists, geneticists and paleontologists got together to discuss how who we are has been shaped by what we eat.
Perhaps the most surprising conclusion was that – despite what some diet gurus may say – there is no &#8220;natural&#8221; human diet. Not only can humans thrive on a wide variety of diets, from the highly carnivorous fare of nomadic Siberians to the virtually all-potato menu consumed by native Peruvians, but thanks to evolution our species can change its diet surprisingly readily.
&#8220;You can find humans living well and healthily from a tremendous diversity of diets,&#8221; said William Leonard, an anthropologist at <a href="http://www.northwestern.edu/newscenter/stories/2009/02/leonard.html" target="_blank" rel="noopener">Northwestern University</a> in Evanston, Ill.
But all cultures have one dietary feature in common, said Harvard University primatologist Richard Wrangham – they cook their food. Wrangham believes the advent of cooking during human prehistory was a major evolutionary milestone, because it essentially pre-digested starches and proteins and softened food, helping increase the amount of energy that could be extracted on it. In fact, he pointed out that people in modern technological societies who take up so-called &#8220;raw food&#8221; diets usually lose substantial amounts of weight.
Many diet books advise following a high-protein, low-carbohydrate diet in order to emulate the eating habits of pre-agricultural humans. Whatever the benefits of such a diet, however, it is clear that in the 10,000 years since the development of farming our genes have responded to the increasing availability of foods such as rice, grains and milk.
&#8220;I would say most people who descend from agricultural populations are actually pretty well adapted to a starch diet, because most of the world eats a lot of rice, a lot of corn and a lot of potatoes, said Anne Stone, a geneticist at Arizona State University.
Stone and her colleagues have studied the gene AMY1, which encodes a salivary protein called amylase that breaks down starch. All people have multiple copies of the AMY1 genes. But those from traditionally agricultural populations, such as the Japanese and Europeans, have many more than those from cultures that have never practiced agriculture.
Customers of 23andMe may be able to see the evolutionary effects of an agricultural heritage in their own genetic data. Before people started herding cattle, goats and sheep, the human biological machinery for digesting milk was turned off not long after infancy – perhaps to prevent older children from getting in destructive fights over breast milk. But with herd animals on the scene, when a genetic modification that kept milk digestion functioning into adulthood arose in Europe around 8,000 years ago, it was so beneficial that it eventually spread throughout the continent.
23andMe customers have one modified version of the lactase gene for each A at the SNP rs4988235.
Similar scenarios happened in several other parts of the world as well, so that now many people of European and some of African ancestry can easily digest large amounts of milk.

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The Most Natural Human Diet: Just About Anything

The Blog has pointed out several times in the last few months that when researchers look for evidence of interbreeding between early humans and Neanderthals, they often fail to find any.
But there are still several geneticists who would like us to heed the words of former defense secretary Donald Rumsfeld, who once pointed out that &#8220;the absence of evidence is not evidence of absence.&#8221;
During a briefing for science writers this morning at Stanford University, geneticist Bruce Lahn argued that interbreeding with Neanderthals may have introduced a mutation that appears to confer an evolutionary advantage about brain development into the human gene pool.
&#8220;We argue that in modern humans, there may actually be some Neanderthal genes,&#8221; Lahn said at the Council for the Advancement of Science Writing&#8217;s New Horizons in Science briefings.

Lahn based his argument on a gene known as microcephalin. Because certain gene mutations can cause brain underdevelopment, microcephalin is assumed to be involved in that organ&#8217;s development.
Lahn described research he and several colleagues first described two years ago in the <a href="https://www.pnas.org/content/103/48/18178.full?sid=a8247834-aa24-4260-b390-4213ac428291" target="_blank" rel="noopener noreferrer">Proceedings of the National Academy of Sciences</a>. The researchers sequenced microcephalin in 89 people from populations around the world. They found that the sequences fell into two very different groups – so different, in fact, that they apparently traced back to a common ancestor older than the human species itself.
Moreover, each of the two groups appeared to have a very distinct history. One appeared to have arisen about a million years ago and diversified at a steady pace since then. The other group appeared to have arisen just 37,000 years ago and spread rapidly throughout 70% of the human population. That kind of pattern suggests what evolutionary biologists call a &#8220;selective sweep,&#8221; the introduction of an advantageous genetic variant that quickly wipes out older versions of the gene.
Usually, when geneticists see a selective sweep in action, the new variant appears to arise out of the pre-existing one. But in this case, Lahn argues, the new genetic variation traces back to a common ancestor that precedes both populations. He believes Neanderthals could have been that population and that they could have transferred the &#8220;new&#8221; variation into the human gene pool through interbreeding about 40,000 years ago.
It&#8217;s just a hypothesis at this point – and one that many geneticists consider challenging to <a href="https://www.nature.com/hdy/journal/v98/n4/full/6800953a.html" target="_blank" rel="noopener noreferrer">confirm</a>. But suppose ongoing efforts to sequence the Neanderthal genome find a version of the microcephalin gene identical to the one currently sweeping through the human population. In that case, Lahn will have strong evidence for his claim.

Did Neanderthals and Humans Mate?

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Before efforts to sequence the human genome began, scientists thought they’d find about 100,000 protein-coding genes in the three billion bases pairs of DNA that are found in almost every cell.
But much to everyone’s surprise, the true number turned out to be much lower. It’s now thought that the human genome contains only about 20,000 protein-coding genes, representing less than 2% of the contents of the genome.
<h6>Ultraconserved Elements</h6>
Much of the remaining 98% of the genome remains a mystery. Some chunks of this DNA are referred to as “ultraconserved elements” because they have remained practically unchanged through hundreds of millions of years of evolution in many species.
It is a basic principle of biology that if something goes unchanged for that long, it ought to be good for something. Yet the function of ultraconserved elements is completely unknown. In fact, laboratory studies in mice have shown that the animals <a href="http://biology.plosjournals.org/perlserv/?request=get-document&#038;doi=10.1371/journal.pbio.0050234&#038;ct=1" target="_blank" rel="noopener noreferrer">do just fine</a> when some of the ultraconserved elements are deleted.
<h6>Humans and Macaques</h6>
To find out if ultraconserved elements really are dispensable, Cory McLean and Gill Bejerano of Stanford University analyzed ultraconserved elements and non-conserved DNA sequences in five mammalian genomes.
Their results, published online today in <a href="https://genome.cshlp.org/cgi/content/abstract/gr.080184.108v1" target="_blank" rel="noopener noreferrer">Genome Research</a>, show that regions of DNA that are identical or very similar between humans, macaques, and dogs are about 300 times less likely to be missing in rats and mice than regions that are not as closely conserved between the primate and dog species.
It’s not that ultraconserved regions are somehow protected from change. The researchers suggest that in the wild, mutations in these elements put affected animals at a disadvantage, causing the changes to be swept away over time by natural selection. But in the lab there isn’t a whole lot of natural selection – in an environment where mice are treated to filtered air, an absence of predators, and all the food and water they could ever want, any loss of fitness due to lost ultraconserved elements doesn’t seem to have any observable consequences.
<h6>What it might mean</h6>
McLean and Bejerano also found that DNA sequences that can be traced farther back in evolutionary time are more likely to be conserved in diverse species today.
“The longer the sequence has been in us, the less likely it is to be lost. It’s almost like the bricks in the foundation of a building, which hold up the rest of the structure,” said Bejerano in a statement.
Detailed new genome sequences from a variety of mammals will allow Bejerano’s research team to further analyze ultraconserved elements and perhaps ultimately understand what it is they are doing in the genome.
“Evolution is a lot of fun,” said Bejerano. “You answer one question, and five others pop up. But one of the most rewarding things to me is the fact that we’re developing a growing appreciation for how much these regions actually matter.”

The Mystery of Ultraconserved Elements

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An animal&#8217;s ability to survive often depends on how well it can avoid predators.   Many species of fish, birds, and mammals have evolved ingenious methods of staying hidden from predators by blending into the background in one form or another.   But what about animals that do the opposite?   How and why would such attention-grabbing features as a lion’s mane, a male deer’s antlers, or a peacock’s tail evolve?   As it turns out, these traits can be explained by something called sexual selection.   Sexual selection is an aspect of evolutionary theory developed by Charles Darwin in the 19th century after he began to notice many traits that were exaggerated, especially among the male members of the species.   Darwin reasoned that within a species, there must be a &#8220;struggle between the individuals of one sex, generally the males, for the possession of the other sex.&#8221;   So in the same way that women may prefer men with broad shoulders, female peacocks prefer their male counterparts to have ornate feathers — the larger the better. Evolutionary biologists have understood the concept of sexual selection for years, but there has been much debate over how this process occurs at the genetic level.   For example, male and female lions have basically the same set of genes. So how are these genes modified such that male lions develop a mane while females do not?   The answer, as it turns out, is surprisingly simple.
 In this week’s issue of Cell, molecular biologists tackled the question of how sexual selection works by examining the genetics of fruit flies. Male fruit flies have evolved a unique coloring pattern on their abdomens that apparently attracts females in the same way that a peacock’s feathers do.   Females lack the markings, yet they have basically the same genome males do. So how is it that the same basic genome (aside from sex chromosomes) can lead males and females to develop different physical traits? According to University of Wisonsin-Madison biologist Sean Carroll, &#8220;The flies did not need new genes … they just changed how males and females use a common set of genes.&#8221; Carroll and his team discovered that while both male and female fruit flies have the genes necessary to create the abdominal coloring pattern, it is only the males who have that gene switched on.   In female fruit flies, this gene lies dormant. “With this particular trait, it evolved by exploiting (genetic) information that was already there to make male bodies different from female bodies,’ explains Carroll. So how does the genetics of a coloring pattern on fruit fly abdomens apply to sexual selection in other species?   According to Carroll and his colleagues, the same genetic mechanisms that are at play in the fruit fly also operate in a multitude of other animals — including lions, deer, peacocks, and even humans.   This study, in showing the genetic means for how sexual selection may operate, illustrates the ingenuity of evolution — how a seemingly simple genetic switch can create such beautiful and elaborate features in the male members of thousands of the world’s species.

evolution — Page 2

The Most Natural Human Diet: Just About Anything

Did Neanderthals and Humans Mate?

The Mystery of Ultraconserved Elements

Is That a Peacock Feather under your Coat … Or are You Just Happy to See Me?

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