University of Arizona

A photomicrograph shows an X chromosome at left, alongside a shrunken Y chromosome. The Y chromosome is passed down exclusively from father to son and can serve as an indicator of male-line human diversity.

Scientists say an African-American male's odd genetic signature suggests that the human Y chromosome's lineage goes back further in time than they thought — perhaps due to interbreeding with other populations such as Neanderthals.

"This really upsets a lot of ideas, but at the same time, it's understandable if we accept that human populations were structured in the past so that there were little pockets of diversity," said Michael Hammer, an evolutionary biologist at the University of Arizona who is one of the authors of a study published in the American Journal of Human Genetics.

The study focuses on the analysis of a DNA sample that was obtained from an African-American living in South Carolina and submitted to the Genographic Project, a National Geographic effort aimed at mapping human origins and migration. The funny thing about this sample is that it didn't match up with any of the previously known genetic signatures for the Y chromosome, which is passed down from father to son.

"Nobody expected to find anything like this," Hammer said in a news release.

A team led by Fernando Mendez, a researcher in Hammer's lab, analyzed more than 240,000 DNA base pairs on the African-American's Y chromosome. A comparison of the differences between the mystery genetic signature and previously known signatures led the team to conclude that the most recent common ancestor for the entire group lived about 338,000 years ago.

That goes further back than the fossil record goes for anatomically modern humans, Hammer said. "The fossil record speaks to 195,000 years or 200,000 years," he said. It also goes further back than the previous date for the most recent common ancestor based on Y-chromosome analysis, which is in the range of 142,000 years.

The researchers followed up on their discovery by searching through a genetic database for African populations, and turned up 11 men from western Cameroon who had virtually the same genetic signature.

Hammer said there could be two explanations for the previously unidentified Y-chromosome type: Either the genetic heritage of anatomically correct humans really does go back much further than what's reflected in the fossil record — or other populations, such as Neanderthals or the more recently identified Denisovans, interbred with modern humans. Anthropologists refer to that pattern of divergence followed by renewed interbreeding as introgression.

The results are "more consistent with introgression of an odd lineage," Hammer told NBC News. Over the past few years, scientists have been coming around to the view that such interbreeding did take place early in the history of our species. Recent analysis of Neanderthal and Denisovan DNA has indicated that a part of their genetic heritage survives in modern-day humans.

Melissa Wilson Sayres, a geneticist at the University of California at Berkeley who played no role in Hammer's study, said the new findings were "exciting" because they pointed to a Y-chromosome lineage more ancient than any others. "They just happened to come across this one Y chromosome that was hidden for so long, and it's very likely that there are more hidden Y chromosomes around the world," she told NBC News.

She said one of the biggest debates in the study of human genetics has to do with how to match mutation rates with time scales — and she expects this latest study to add to the debate. For example, some might continue to argue that the most recent common ancestor lived more recently than 338,000 years ago. "It will still be the oldest Y-chromosome heritage that we have, but I can foresee that some people might disagree with that specific age," she said.

More about our genetic origins:

• Y chromosome is an evolutionary marvel
• Humans had sex with now-extinct relatives
• So who didn't have sex with Neanderthals?

In addition to Hammer and Mendez, the authors of "An African American Paternal Lineage Adds an Extremely Ancient Root to the Human Y Chromosome Phylogenetic Tree" include Thomas Krahn, Bonnie Schrack, Astrid-Maria Krahn, Krishna R. Veeramah, August E. Woerner, Forka Leypey Mathew Fomine, Neil Bradman, Mark G. Thomas and Tatiana M. Karafet. The authors acknowledged Jacqueline Johnson and her male cousins, the descendants of Albert Perry (South Carolina) and participating Family Tree DNA customers.

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

Mandel Ngan / AFP - Getty Images file

A skull from an ancient specimen of Homo sapiens (foreground, right) is compared with a Neanderthal's skull at the Smithsonian's National Museum of Natural History in Washington. Researchers suggest that a gene linked to the immune system played a roundabout role in brain evolution.

Scientists say our genes contain the hints of an evolutionary tug of war that took place in the wombs of our ancestors, balancing the drive to bigger brains with the need for a strong immune system.

The push and pull of these genetic variants apparently became more pronounced after pre-humans branched off from the ancestors of chimpanzees, according to biologists Peter Parham of Stanford University and Ashley Moffett of the University of Cambridge.

Two years ago, Parham and other researchers suggested that interbreeding with now-extinct cousins such as Neanderthals and Denisovans may have given early humans a boost of immunity. Parham says the same kind of cross-species hanky-panky may have played a role in the genetic diversity that he and Moffett discuss in a paper published online by Nature Reviews Immunology.

"It quite nicely dovetails with all this other stuff," Parham told NBC News. "There is an inherent instability in the way the underlying mechanism works."

How natural killers work
The two biologists focus on how particular types of white blood cells, known as natural killer cells, work in the human immune system. In addition to fighting infections and tumors, natural killer cells help regulate the growth of the placenta during pregnancy. Humans are unique among primates in having two variants of the genes that control the receptors for natural killer cells.

"B haplotypes are favored during reproduction. A haplotypes are more specialized toward defending against infections," Parham explained. "These are subtle effects. On average, if you're an individual that has two A haplotypes and no B haplotype, you're going to have a slightly more robust immune system in terms of dealing with disease."

Having two B haplotypes, in contrast, would allow for a more robust placenta. That would provide the fetus in the womb with more of the nutrients needed to grow a bigger brain. "In the course of human evolution, you had the evolution of these B haplotypes, which really did enable the brain to get bigger. ... There are correlations between the size of the brain of the baby and these genetic factors," Parham said.

A detailed analysis of human genetic diversity suggests that the genes for the B haplotype emerged in the time frame lasting from about 7 million years ago to 1.7 million years ago. That would cover a period starting with the divergence of human and chimp ancestors, and ending with the human migration out of Africa.

The A-vs.-B breakdown is found in all present-day human populations, suggesting that both variants were important to have for different situations. Parham and Moffett speculate that the A variant was important when a population was facing a disease epidemic, while the B variant became important for brain-building once the epidemic passed.

The role of the birth canal
When our ancestors began walking upright, that introduced another push-pull effect for brain size. "It's difficult to document, but it's generally thought in the field of obstetrics that birthing is more difficult for humans than it is for other species," Parham said. The dimensions and layout of the human birth canal is one constraint: If a baby's skull were to get significantly bigger, it wouldn't fit through the canal.

Another constraint is pregnancy's effect on the mother's cardiovascular system. In some situations, a potentially fatal condition known as preeclampsia can occur.

"Part of the compromise is that the human population has tolerated a certain amount of death in childbirth, due to obstructed labor or preeclampsia. ... Both of these types of death in childbirth have been quite common in our species, as has been documented in so many 19th-century novels," Parham said.

The genetic record indicates that the human species passed through a series of "bottlenecks" in prehistoric times that reduced population diversity to perilously low levels. That's where interbreeding with Neanderthals could have played a part. "One way that modern humans replenished the genetic diversity lost in populations was through the selection of new variants ... another, and possibly more effective, mechanism was to acquire old variants by mating with archaic humans," Parham and Moffett write.

Today, modern medicine has leveled the evolutionary playing field. But in ancient times, all these genetic and physiological factors seem to have interacted to make our brains what they are today.

"Basically, we've got the nervous system and the brain putting pressure on the immune system and the reproductive system," Parham said.

More about human evolution:

• How sex with Neanderthals made us stronger
• Where did we get the energy for big brains?
• Brawn may have boosted the human brain

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

Primate researchers in Georgia have laid out what they say is the best laboratory evidence yet that chimpanzees have a human-style sense of fairness. Other researchers, however, say the study is flawed — and they're sticking to their view that fairness may be a uniquely human characteristic.

The debate focuses on a key question about human evolution: How long ago did our ancestors acquire what Abraham Lincoln called the "better angels of our nature"? These angelic traits — such as altruism, empathy and fairness — manifest themselves in behaviors that can run counter to our own self-interest.

The latest research, published in the Proceedings of the National Academy of Sciences, argues that a sense of fair play may have arisen millions of years ago, before our ancestors split off from the evolutionary line leading to other primates. The study's principal author, Darby Proctor of Emory University's Yerkes National Primate Research Center in Atlanta, told NBC News that the research "opens up the door for exploring the evolutionary roots of fairness in non-human animals."

"We've concluded that chimpanzees not only get very close to the human sense of fairness, but the animals may actually have exactly the same preferences as our own species," co-author Frans de Waal, director of Emory's Living Links Center, said in a university news release.

However, the Emory group's findings run counter to what other researchers have found in their own experiments over the past few years. One of the researchers behind those earlier studies, Keith Jensen of the University of Manchester, has said "our sense of fairness is a derived trait and may be unique to the human race."

Today, Jensen said he and his colleagues had serious reservations about the latest experiment. "I was excited to see a replication of our ultimatum game studies, seven years on, but was disappointed by the results," he told NBC News in an email.

How the experiment was run
The "ultimatum game" is a key concept in all these studies: The concept refers to an arrangement in which one player makes a proposal to another player to split up a reward. For example, a parent may offer six stickers to a little girl, on the condition that she divides the treasure with her brother. A researcher may offer six banana slices to a chimp, on the condition that it divides the goodies with another chimp.

Emory University

Researchers report that chimpanzees can change their strategy for dividing goodies, based on whether or not the chimps they're sharing with have any say over the deal.

If the shares are totally determined by the little girl, or the first chimp, their offer to the partner tends to be as low as possible. That's what's known as the "dictator game." But if the other partner has the power to veto a deal, it gets more complex. Make too low of an offer, and the partner might reject the proposition out of spite — even though the result is that no one gets a reward. That's the "ultimatum game."

The Georgia researchers ran a variety of games using tokens that could be traded for either equal or unequal shares of stickers (for 20 human children, ranging in age from 2 to 7) and bananas (for six adult chimpanzees). The researchers found that the results of the game were similar for the two groups.

If the one offering the goodies was in full control of the split, that individual kept the lion's share of the goodies. The results were different if the two partners had to agree on the split, however. "Humans typically offer generous portions, such as 50 percent of the reward, to their partners, and that's exactly what we recorded in our study with chimpanzees," Proctor said.

How the debate is playing out
Some questions surround the study: The second partner in the ultimatum game always accepted the offer of a split, whether it was equal or unequal. That applied to the kids as well as the chimps. Such behavior might suggest that the recipients would be happy with whatever they got, and didn't care about the fairness of the deal.

In Jensen's eyes, the fact that none of the chimps turned down an unequal split is a "fatal flaw."

"The ultimatum game hinges on the responder," Jensen said. "If the responder didn't understand the option of refusing, I would simply say the study did not work." Similarly, the children involved in the study may have been too young to understand that they could turn down an unfair deal — something that Proctor and her colleagues admit in their study.

They did report, however, that both the chimps and the children occasionally expressed displeasure about an unequal division. For the kids, it was voiced in complaints such as "You got more than me!" For the chimps, it took the form of spitting water at their selfish partner, or hitting a barrier between their cages.

Proctor and her colleagues cite other studies to back up their claim that chimps are sensitive to unfairness — such as anecdotal, non-experimental reports of chimps negotiating over the division of meat, or leafy branches. But such reports aren't yet rigorous enough to resolve the debate.

Proctor acknowledged that more research will be required to get a firmer grasp on the better angels of a chimpanzee's nature. "We can't be sure what all was going on between the chimps," Proctor said. "That's something we'd really like to explore in the future — how much communication is necessary to convey something to another chimp."

More about the better angels of animal nature:

• How monkeys handle moral outrage
• Sense of fairness goes back to monkeys
• What chimps can teach us
• Dogs can think 'no fair' too

In addition to Proctor and de Waal, the authors of "Chimpanzees Play the Ultimatum Game" include Rebecca Williamson and Sarah Brosnan.

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

Oxford Scientific / Getty Images Stock

Researchers found that it was easy to breed guppies with bigger brains, but the fish had smaller guts and also produced fewer progeny. The results serve as experimental evidence of evolutionary trade-offs.

Scientists have long suspected that big brains come with an evolutionary price — but now they've published the first experimental evidence to support that suspicion, based on their efforts to breed big-brained fish.

A Swedish team found it relatively easy to select and interbreed common guppies to produce bigger (or smaller) brains — as much as 9.3 percent bigger, to be precise. But the bigger-brained fish also tended to have smaller guts and produce fewer babies.

This finding is consistent with what's known as the "expensive-tissue hypothesis" — the idea that there's a trade-off between the demands of the brain and the demands of other organs. For example, we humans have bigger brains than other primates, relative to body size. About 20 percent of the energy we take in is used up by the brain, which represents just 2 percent fo our body mass. But the amount of energy devoted to digestion is smaller, relatively speaking.

Some evolutionary biologists have speculated that when our distant ancestors shifted to an easier-to-digest diet, that freed up the energy for bigger brains. But that speculation has been based primarily on comparative studies of brain size and gut size as they are in present-day species. And some of the recent studies on the subject have been interpreted as refuting the expensive-tissue hypothesis.

Niclas Kolm and his colleagues at Uppsala University used artificial evolution — that is, selective breeding — to show the tissue trade-off in action. Their results were published online today by the journal Current Biology.

The experiment put 48 of the guppies through an underwater arithmetic test to see whether better cognitive abilities came with the bigger brains. It turned out that the brainier fish were better at learning to recognize how many geometric symbols were on a door in order to get to the food on the other side (at least if there were up to four symbols).

But in the gut-size department, the bigger-brained fish, especially the males, came up short (20 percent smaller for males, 8 percent for females). What's more, the big-brained fish had 19 percent fewer offspring than the small-brained fish. That result suggests that bigger brains are somehow associated with smaller broods — a phenomenon that researchers have noticed with regard to primates as well as cetaceans.

Although the raw numbers seem to support the expensive-tissue hypothesis, Kolm and his colleagues weren't able to tease out the genetic mechanism for the trade-off. Thus, it's not fully clear which comes first: smaller guts or bigger brains. 

"Our results on the guppies demonstrate that the order of evolutionary transitions is starting with a change in brain size, followed by a decrease in gut size," Kolm told NBC News in an email. "At the same time, this does not automatically mean that the opposite response is not also possible. To test this would of course require further experiments. Currently, our cautious conclusion is that we have identified a new possible direction of events in that selection for increased brain size may indeed have 'forced' a reduction in gut size."

The same caveat goes for the findings on reproduction. Kolm said he and his colleagues interpret their results as supporting the view that reduced reproductive capacity is one of the evolutionary costs associated with bigger brains.

"This would seemingly suggest a lower fitness in large-brained individuals, which would not be intuitively 'possible' from an evolutionary point of view," Kolm acknowledged. "Here it is important to remember that in our selective set-up, we have no additional selection pressures from avoiding predators, finding food, competing for mates, etc., that would occur in the natural environment. Hence, there might still be an overall fitness benefit from increased brain size in the wild, at least in certain environments/situations, that would allow selection for increased brain size despite the lowered fecundity."

The Swedish researchers are planning a new round of experiments to see how big-brained (and small-brained) guppies handle a more realistic evolutionary environment.

"Watch this space," Kolm said.

More about brains and evolution:

• How diet affected human evolution
• Theory says humans are losing intelligence
• Flash interactive: Take a tour of your brain
• Gallery: The 10 smartest animals

In addition to Kolm, the authors of "Artificial Selection on Relative Brain Size in the Guppy Reveals Costs and Benefits of Evolving a Larger Brain" include Alexander Kotrschal, Björn Rogell, Andreas Bundsen, Beatrice Svensson, Susanne Zajitschek, Ioana Brännström, Simone Immler and Alexei Maklakov.

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

U.S. Rep. Paul Broun's view that the theories of evolution and the big bang are "lies straight from the pit of Hell" is getting more exposure than he might have expected, thanks to a video that was made at a church-sponsored banquet in Georgia and distributed by a progressive political watchdog group.

The Georgia Republican is already well-known as an outspoken conservative Christian, due in part to his unsuccessful campaign to have 2010 declared "the Year of the Bible." But the latest comments have taken on an extra dab of controversy because Broun, a medical doctor, calls himself a scientist in the video and chairs the House Science Committee's panel on investigations and oversight.

The video clip, distributed by the Bridge Project, was taken from a longer version recorded on Sept. 27 during the 2012 Sportsman's Banquet at Liberty Baptist Church in Hartwell, Ga. Here's a transcript of the Bridge Project's snippet:

"God's word is true. I've come to understand that. All that stuff I was taught about evolution and embryology and the big bang theory, all that is lies straight from the pit of Hell. And it's lies to try to keep me and all the folks who were taught that from understanding that they need a savior. You see, there are a lot of scientific data that I've found out as a scientist that actually show that this is really a young Earth. I don't believe that the earth's but about 9,000 years old. I believe it was created in six days as we know them. That's what the Bible says.

"And what I've come to learn is that it's the manufacturer's handbook, is what I call it. It teaches us how to run our lives individually, how to run our families, how to run our churches. But it teaches us how to run all of public policy and everything in society. And that's the reason as your congressman I hold the Holy Bible as being the major directions to me of how I vote in Washington, D.C., and I'll continue to do that."

Broun's comments were greeted with applause, and they probably reflect how a lot of his constituents feel about the same issues. He's assured of re-election in any case, due to the fact that he has no Democratic Party challenger in next month's election. But how will Broun's latest pronouncements play out on a national stage? Will they have any effect on the presidential campaign? Feel free to weigh in with your comments below.

Update for 11:35 p.m. ET Oct. 6: The Athens (Ga.) Banner-Herald said Meredith Griffanti, a spokeswoman for Broun, referred to the video in this brief, emailed statement: "Dr. Broun was speaking off the record to a large church group about his personal beliefs regarding religious issues." 

More about science and politics:

• Doctors appalled by candidate's comments on rape
• Presidential science quiz rekindles climate debate
• Is the scientific perspective like political poison?
• More campaign news from NBC Politics

Tip o' the Log to Talking Points Memo and Scientific American Observations.

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

M. Hofreiter / K. Fiusterweier

Researchers say some Neanderthals may have had pale skin and red hair similar to that of some modern humans. Explaining the genetic similarities, however, can lead to a tangled tale.

One of the most titillating tales in the study of human origins — focusing on whether Neanderthals interbred with modern humans — has just gotten more tangled.

Over the past couple of years, studies of Neanderthal DNA samples painstakingly extracted from ancient bones have suggested that contemporary non-Africans can trace up to 4 percent of their genetic code to our long-extinct Neanderthal cousins. The genomes of modern-day Africans, in contrast, have virtually nothing in common with the Neanderthals. Researchers assumed that the genetic contribution for the non-Africans was passed down through cross-species sex during the time that Neanderthals and Homo sapiens lived in close proximity in Europe, tens of thousands of years ago.

However, there's another possibility: Maybe that common genetic code was passed down from the common ancestor of Homo sapiens and Homo neanderthalensis, hundreds of thousands of years ago in Africa. Today, researchers at the University of Cambridge reported in the Proceedings of the National Academy of Sciences that such a scenario provides a better fit for the genetic data. They say there's no need to assume that anatomically modern humans did the Neanderthal nasty, a process known more scientifically as hybridization. 

"Our work shows clearly that the patterns currently seen in the Neanderthal genome are not exceptional, and are in line with our expectations of what we would see without hybridization," the lead researcher, Andrea Manica, said in a Cambridge news release. "So, if any hybridization happened — it's difficult to conclusively prove it never happened — then it would have been minimal and much less than what people are claiming now."

Modeling population dynamics
Manica and his colleagues set up a computer model for the last half-million years of population dynamics, with the assumption that there were two migrations from Africa. The first migration led to the settlement of Europe by the ancestors of the Neanderthals, hundreds of thousands of years ago. Then, around 300,000 to 350,000 years ago, the route from north Africa to Europe was cut off somehow. The European and north African populations showed gradual genetic divergence, but still retained a bit of common heritage from their mutual ancestors.

When the second migration from Africa took place, around 60,000 to 70,000 years ago, the north Africans who dispersed to Europe and Asia would carry that extra bit of genetic similarity with them. But the Africans who lived farther south and stayed behind on the continent wouldn't have as much genetic kinship with the Europeans.

The researchers found that their model did a fine job of accounting for the existing data without Neanderthal sex.

So what do the researchers behind the earlier DNA studies say? That's where it gets really interesting: One study, published online in April in Molecular Biology and Evolution, contends that ancient population dynamics alone can't account for the genetic patterns seen in the DNA from Neanderthals and modern humans. Another study, posted on the arXiv preprint server and due for publication in PLOS Genetics, takes a closer look at a genetic pattern known as linkage disequilibrium — and concludes that modern humans and Neanderthals interbred somewhere between 37,000 and 86,000 years ago. Nature's Ewen Callaway delves into the details surrounding those claims and counterclaims.

Either-or proposition?
So, to recap: Some scientists say the population dynamics that were in effect hundreds of thousands of years ago can explain genetic similarities between populations, even if those populations never interbred. Others say the evidence is getting stronger that modern humans and Neanderthals really did mate when they met up in Europe, tens of thousands of years ago.

University of Washington geneticist Joshua Akey says both sides just might be right.

"To me, I don't think it's a case of either-or," he told me. "I think that both things can be going on."

Akey and other researchers recently published a study in the journal Cell suggesting that a mysterious "Neanderthal sibling species" made a genetic contribution to the DNA of modern-day Africans. He said that interpreting whether genetic similarities come from a common ancestor (a process known as archaic population structure) or from more recent cross-species sex (a process that Akey calls introgression) is a tricky but essential task for those who study human origins.

"Ultimately, it's important that we come to a consensus as to one process or the other, but I find them both to be interesting interpretations," Akey said. "Introgression is a sexier mechanism, but even if it turns out to be a case of archaic population structure, that still tells us something about our past that we didn't know before."

So did modern humans do it with Neanderthals or not? And to what extent? Today, maybe it's a tangled tale, but that won't necessarily be the case forever. Akey said he was optimistic that researchers will be able to "tease apart" the different influences from the two processes within the next year or so.

Update for 2:10 a.m. ET Aug. 14: In a follow-up email, Akey clarified his view on the "did they do it" question, leaning toward the affirmative:

"Although I do think that both ancestral population structure and introgression are not mutually exclusive events, the recent papers from David Reich and Monty Slatkin show pretty compelling evidence that introgression of Neanderthal lineages into anatomically modern humans occurred. Thus, the real debate moving forward will be about the relative contributions of these two processes."

More about ancient hominid sex:

• Neanderthal-human sex rarely produced kids
• Ancestors had sex with mysterious human cousins
• How sex with Neanderthals made us stronger

Cambridge's Anders Eriksson is Manica's co-author on the paper published by the Proceedings of the National Academy of Sciences, titled "Effect of Ancient Population Structure on the Degree of Polymorphism Shared Between Modern Human Populations and Ancient Hominins."

Authors of the study in Molecular Biology and Evolution are Melinda Yang, Anna-Sapfo Malaspinas, Eric Durand and Montgomery Slatkin.

Authors of the preprint destined for PLOS Genetics are Sriram Sankararaman, Nick Patterson, Heng Li, Svante Pääbo and David Reich.

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the dwarf planet and the search for new worlds.

Jason Hatfield / Reuters

People hold a prayer vigil for the victims and first responders as police investigate an overnight shooting that killed 12 people at a midnight premiere of the new "Batman" movie in Aurora, Colo., on July 20.

Why did a dozen people die in this week's "Dark Knight" shootings? What was going on inside the head of James Eagan Holmes, the former neuroscience student who's suspected of killing those people in a movie theater in Aurora, Colo.? Questions about Holmes and his motives are the big unanswerables right now — but some folks are already suggesting that higher powers are at work. Higher powers like ... Charles Darwin?

"When students are taught they are no different from animals, they act like it," Rick Warren, the mega-church pastor and inspirational author, observed in a Twitter update just hours after the shootings.

That tweet came amid a flurry of homespun aphorisms and Bible quotes, so it's not fully clear that Warren was specifically blaming the violence on the teaching of evolutionary biology in schools. But the comment stirred up a hornet's nest among the theory's champions, including the University of Chicago's Jerry Coyne.

"I doubt that religion had anything to do with these murders, but religion is so quick to point the finger at science and evolution when they happen," Coyne wrote on his "Why Evolution Is True" blog. "So much for Rick Warren, the man Barack Obama chose to give the invocation at his inauguration in 2009."

'Where was God in all of this?'
Warren's comment wasn't the only one that seemed to touch on the link between godlessness and divine retribution. Rep. Louie Gohmert, R-Texas, brought up the link when he was asked about the Colorado shootings on the "Istook Live" radio show:

"We have been at war with the very pillars, the very foundation of this country ... and when ... you know ... what really gets me as a Christian, is to see the ongoing attacks on Judeo-Christian beliefs and then a senseless crazy act of terror like this takes place," Gohmert said, according to a transcript on his House website.

"You know, when people say, where was God in all of this?" he said. "Well, you know, we don’t let ... in fact, we’ve threatened high school graduation participants that if they use God’s name that they’re going to be jailed, we had a principal of a school, and a superintendent or a coach down in Florida that were threatened with jail because they said the blessing at a voluntary off campus dinner. I mean, that kind of stuff ... where is God? Where, where? What have we done with God? We told him that we don’t want him around. I kind of like his protective hand being present."

Those comments drew a denunciation from the American Humanist Association — an organization whose slogan is "Good Without a God."

"Rep. Louis Gohmert truly tortures logic when he concludes that this violence had something to do with perceived attacks on majority faith in America," said Roy Speckhardt, the association's executive director. "At a time when families are mourning in the wake of this tragedy, Gohmert used it as an opportunity to push a religious agenda."

Christian? 'What a scary thought'
On the flip side, some atheists suggested that Christianity was to blame, capitalizing on reports that Holmes came from a Presbyterian family. On the "Debunking Christianity" blog, Cathy Cooper argues that Christian belief encourages the idea that all people are sinful, but that all believers are saved by faith alone. "Christianity provides believers with a basis for the belief that they are absolved from taking responsibility for their own bad behavior," she writes.

"Yes, James Holmes was a 'normal Christian boy' — what a scary thought," Cooper says.

Comments like that cause P.Z. Myers, a biologist at the University of Minnesota at Morris who describes himself as a godless liberal, to hang his head in shame.

"Christianity is piss-poor at doing more than providing lip-service against violence, but it’s at best a passive enabler." he wrote on his Pharyngula blog. Myers said the blame should instead be directed at a culture that glorifies violence, at laws that make it easy to acquire deadly weapons— and most of all, at the person who did all the shooting.

"Anything else is a distraction from correcting the real causes," he wrote.

As Ecclesiastes says...
There's nothing new under the sun when it comes to blaming God or godlessness for a disaster. Here are a few recent examples:

• Former House Majority Leader Tom DeLay once said that the 1999 Columbine school shootings in Colorado happened “because our school systems teach our children that they are nothing but glorified apes who have evolutionized out of some primordial mud."
• After Hurricane Katrina hit the Gulf Coast in 2005, Alabama state Sen. Henry E. "Hank" Erwin Jr. observed that the region has "always been known for gambling, sin and wickedness. ... It is the kind of behavior that ultimately brings the judgment of God."
• Evangelical preacher and one-time presidential candidate Pat Robertson blamed a number of disasters on God's wrath — including 2010's catastrophic Haiti earthquake, which he attributed to that country's "pact to the devil."
• Later that year, when an oil spill hit the Gulf of Mexico, Christian doomsayer Hal Lindsey cited the environmental catastrophe as "evidence that when you turn your back on Israel, especially when you've been a supporter, you're gonna see judgments come from God."

Natural catastrophes, and especially human-caused catastrophes like the one that took place this week, do pose a huge challenge for believers: Why does God allow the existence of seemingly senseless evil? If the power of prayer can save some believers, why would He be so cruel as to leave others unsaved? Do believers really think that the dead were more sinful than the living?

God doesn't own a gun
Marie Isom has a unique perspective on these questions: Not only is she a Christian and a blogger — she's also a survivor of the theater shootings. In a gripping post to her blog, "A Miniature Clay Pot," she recounts how she and her daughters were caught up in the chaos, threw themselves to the floor, and scrambled out of the theater when there was a break in the gunfire.

The blog posting is titled "So You Still Think God Is a Merciful God?" Here's the answer she gives:

"Yes.

"Yes, I do indeed.

"Absolutely, positively, unequivocally.

"Let’s get something straight: the theater shooting was an evil, horrendous act done by a man controlled by evil.  God did not take a gun and pull the trigger in a crowded theater. He didn’t even suggest it. A man did.

"In His sovereignty, God made man in His image with the ability to choose good and evil.

"Unfortunately, sometimes man chooses evil."

If you're looking for some appropriate Sunday reading after a horrendous couple of days, you couldn't do much better than Isom's essay and her follow-up posting. I realize there's not much science in it, but that's why we call it Cosmic Log rather than Science Log.

Feel free to leave your comments and condolences in the space below. 

Update for 1:15 a.m. ET July 22: There's more blame to go around. Jerry Newcombe of Truth in Action Ministries said in a commentary on the shootings that "we're reaping as we're sowing in this society."

"We said to God, 'Get out of the public arena,'" he wrote. "Lawsuit after lawsuit, often by misguided 'civil libertarians,' have chased away any fear of God in the land — at least in the hearts of millions." The result, Newcombe said, is that young people no longer dread the loss of Heaven or the pains of Hell.

"I don't think people would do those sorts of things if they truly understood the reality of Hell," he wrote.

The news director of the American Family Association, Fred Jackson, followed up with Newcombe on the "AFA Today" radio show. About 10 minutes into the show, Jackson said this:

"In the community there were community standards that reflected biblical principles, whether people knew it or not, the standard in the community was based on scripture. In that short period of time, roughly 40 years, we have seen such a transformation in values in our communities, whether it’s rural or whether it’s big city. I have to think that all of this, whether it’s the Hollywood movies, whether it’s what we see on the Internets, whether it’s liberal bias in the media, whether it’s our politicians changing public policy, I think all of those somehow have fit together — and I have to say also churches who are leaving the authority of scripture and losing their fear of God — all of those things have seem to have come together to give us these kinds of incidents."

Later in the show, around the 44-minute mark, Jackson added to the list of contributing factors:

"I think the source of this is multifaceted, but you can put it all, I think, under the heading of rebellion to God, a rejection of the God of the Bible. I think along with an education system that has produced our lawyers, our politicians, more teachers, more professors, all of that sort of thing, is our churches, mainline churches. ... The AFA Journal has been dealing with denominations that no longer believe in the God of the Bible, they no longer believe that Jesus is the only way of salvation, they teach that God is OK with homosexuality. This is just increasing more and more. It is mankind shaking its fist at the authority of God."

The Right Wing Watch and Gawker websites both picked up on these observations, and Right Wing Watch helpfully provides audio excerpts of the relevant quotes. (However, you can listen to the whole 54-minute show on iTunes for free.) Gawker's Louis Peitzman writes that "this message isn't just offensive: it's impossibly muddled," and he wonders whether anyone believes this sort of thing anymore. I think there are a lot of people who do. But what do you think? 

Related content from NBCNews.com:

• Suspect was once a camp counselor for kids
• Will Batman shooting suspect ever face trial?
• Police deactivate trap at suspect's apartment
• Six-year-old among those killed in massacre
• Victims include sailor, aspiring sportscaster
• Cops: Weeks of planning went into shootings
• Survivor: Boyfriend 'took a bullet for me'
• Full coverage of the Colorado shootings

For a completely different take on the questions surrounding the "Dark Knight" shootings, God and even Batman, check out Paul Asay's essay on The Washington Post's website. Asay is the author of "God on the Streets of Gotham: What the Big Screen Batman Can Teach Us About God and Ourselves."

Tip o' the Log to my colleague at NBCNews.com, Bill Dedman.

 Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the dwarf planet and the search for new worlds.

HBO

A freshly hatched dragon perches on the shoulder of Daenerys in "Game of Thrones."

This the Year of the Dragon, and not just because of the Chinese calendar: Dragons play big roles in HBO's "Game of Thrones" TV series as well as the upcoming film version of "The Hobbit." Those fire-breathing, leathery-winged reptiles have been gripping the human imagination with their sharp talons for millennia, and it's worth wondering why.

Some folklorists trace the dragon myth back to a variety of sources in ancient China, Rome, Greece and India, and speculate that it had its genesis in the discovery of fossil bones from the strange creatures we now know as dinosaurs:

• Scythian lore described griffins with lionlike bodies and birdlike beaks. In the year 77, Pliny the Elder passed down the Scythian stories of gold-guarding griffins with peculiar ears and wings.
• During his travels in northern India, the first-century Greek philosopher Apollonius of Tyana reported that "no mountain ridge was without" a dragon to its name. The locals said they used magic to lure the dragons out of the earth and pry out the gems embedded in their skulls.
• Chinese accounts of "dragon bones" go back thousands of years — and as recently as 2006, ground-up dinosaur bones were being used in traditional medicine by villagers who believed they came from dragons. (The hard-to-crack dragon eggs depicted in "Game of Thrones" may well trace their lineage back to fossilized dinosaur eggs.)

Classical folklorist Adrienne Mayor, who relates all these tales in her book "The First Fossil Hunters," ascribes the reports to discoveries in fossil-rich regions such as the Altai Mountains in Central Asia, the Gobi Desert in China and Mongolia, or the Siwalik Hills in the Himalayas. Not knowing any better, adventurers interpreted the dinosaur bones as representing the remains of dragons, griffins and other mythical monsters.

The gold hoarding? That may have arisen because gold deposits were found close to the fossil beds along ancient Issedonian trade routes.

And the gems? "I think the Indian lore about special gems prised out of dragon skulls alludes to the crystals that can form on mineralized bones," Mayor wrote. "The detailed observations of the first modern investigator of the Siwalik fossils confirm my theory: large, glittering calcite crystals and tubular selenite crystals are common in the Siwalik fossils."

Hard-wired for dragons?
Anthropologist David Jones went even further in his book "An Instinct for Dragons," published in 2000: He proposed that the fables about winged, poison-spewing, fanged and clawed creatures combined three of the top threats to ancient pre-human primates: raptors like the one that may have preyed on a now-fossilized ape-boy known as the Taung child nearly 2 million years ago; poisonous snakes like the ones that may have driven the evolution of big brains and improved vision in primates millions of years ago; and big cats like the ones our pre-human ancestors had to watch out for in Africa.

"The world-dragon was formed by the nature of our own shadowy progenitors' encounters with the creatures who hunted them over millions of years," Jones wrote. The way he sees it, our brain came to be hard-wired with an instinctive fear of dragons.

Paul Jordan-Smith, a folklorist and storyteller who wrote a fiery critique of Jones' book for the journal Western Folklore, thinks the idea that our ancestors somehow evolved a dragon instinct just doesn't hold up. For one thing, Jones' claim that multiple cultures had the same conception of dragons as dangerous beasts is "demonstrably untrue," he said.

"My take on the mythic image of the dragon is that there is no one 'authentic' image, and no one 'true' meaning," Jordan-Smith told me in an email. "The dragon has been a guardian, a thief, a hoarder (like Smaug, in 'The Hobbit') and a dispenser of wisdom (especially in Chinese tales)."

For another thing, the dragon doesn't show up fully formed in ancient tales.

"It's interesting that dragons do not appear in cave paintings," Jordan-Smith wrote. "What does appear are the beasts that they hunted or that were dangerous. ... Where you do see constructs that aren't literal depictions, they're of humans merged with animals. And when you get civilization, you don't see dragons until much later. ... You don't get dragons until you get stories that have dragons in them."

Who's gripping whom?
But once dragons become part of a culture's mythic milieu, they don't fade away. Perhaps that explains why dragons hang around, in Chinese New Year festivals, in European fairy tales, and in American movies and TV shows. Here's what Jordan-Smith had to say about that:

"A dragon, like most mythic imagery, is 'plastic,' in the sense of being adaptable. It can look like whatever the singer of tales wants it to, can serve whatever purpose needed, and can mean just about anything. And some of the traditional qualities may not be incompatible with one another. A dragon that guards a treasure (or an abducted maiden) may be waiting for the right hero that will liberate it from its responsibility. A dragon that threatens to destroy a village may be a wake-up call to rectify misdeeds. Some dragons are enchanted and must be slain to regain their true form. But not all dragons are meant to be slain.

"And what of the hero? He must be changed somehow by the encounter, or else the game is not worth the candle. But what kind of change? In some cultures, to slay a fearsome beast was tantamount to assimilating its powers. ... In Tolkien's books, the Ring exerts its power so thoroughly that its wearer little by little becomes like Gollum. Perhaps there's a particular kind of danger, much more deadly than merely being killed. And perhaps when the hero slays the dragon, he himself is slain, to be reborn as the human incarnation of the dragon. For good or ill? Ask the storyteller."

Maybe it's not the dragon that has a grip on us. Maybe we're the ones who are hanging onto the dragon — and we don't want to let go.

More about dragons and 'Game of Thrones':

• Origin of Komodo dragons revealed
• Chinese villagers ate dinosaur 'dragon bones'
• Sword science plays a role in 'Game of Thrones'
• All about 'Game of Thrones' on The Clicker

Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or adding Cosmic Log's Google+ page to your circle. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for other worlds.

Steffen Wischmann / University of Lausanne

Researchers used a simulated version of these two-wheeled robots with flashing lights to show how randomness in the occurrence of genetic traits can drive evolution of language.

Even if everything about different groups of animals is identical down to the level of their genes and physical surroundings, they can develop unique ways to communicate, according to an experiment done with robots that use flashing lights to "talk."

The Swiss researchers used the robots to get handle on why there is such diversity in communication systems within and between species, something that is difficult to do in living animals. 

The answer, they found, "is contingencies in evolutionary history, i.e. stochasticity (randomness) in the occurrence order of new ... traits," Steffen Wischmann, a researcher in the department of ecology and evolution at the University of Lausanne, told me in an email.

He and his colleagues started with 20 populations of identical two-wheeled robots each equipped with a camera, a food detection sensor, a simple information processing program, and a ring that could emit a blue or green light.

These robots, grouped in populations of 20 individuals, were placed in an arena containing a food source. The team ranked each robot according to how long they spent at the food source. 

They then used a "standard roulette-wheel selection algorithm" to select 100 robots' programs, or genes, for reproduction, according the paper published this week in the Proceedings of the National Academy of Sciences.

"Because the 'genes' — which encoded specifications of the robots neural controllers, responsible for processing sensory information and producing motor actions — were initially set to random values, the robots behaved unpredictably at first," the journal explains in a news advisory.

"But after 1,000 generations, all 20 populations emitted light to indicate food location. In approximately half the populations, the robots emitted a signal only in the presence of food, while the other populations also emitted a different color light in areas without food."

It turned out that the one-signal robots were the most efficient communicators — they found the food faster — but they were also the weakest competitors when pitted against other groups of robots who communicated with two flashing lights.

In other words, there's a tradeoff between communication efficiency and competitive robustness, the researchers note. And, randomness in evolutionary history can affect the outcome of competition between populations.

"Since the two-signal populations use both signals they can also utilize the signals of other populations independent of which signal this other population uses to signal the presence of food," Wischmann explained to me.

Further analysis of the data gleaned from the robots shows that the signaling differences occurred early in the robots' evolution. 

This randomness in the occurrence of mutations can drive the evolution of language and "might also be involved in speciation processes," the team concludes.

More on language evolution:

• Robots invent their own spoken language
• Grow a new language in your head
• A baby's babble leads to language
• Mice given 'human' version of speech gene

John Roach is a contributing writer for msnbc.com. To learn more about him, check out his website. For more of our Future of Technology series, watch the featured video below.