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.

Experts say the premise behind "Rise of the Planet of the Apes," the latest movie about intelligent chimps gone wild, is almost laughable. But they're not laughing about the wider issues raised by the cross-species romp — ranging from the genetic humanization of other animals, to the way we treat our fellow apes, to the long-running debate over the definition of "humanness."

Let's start by acknowledging that there's no way just administering a drug or fiddling with a few genes can confer human-type intelligence or language ability on chimpanzees or other non-human primates. "The scientific notion is preposterous," Jon Cohen, author of the book "Almost Chimpanzee," told me today.

Cohen said the oft-cited claim that there's a 1 percent difference between the human and chimp genetic code has led people to believe mistakenly that the two species are separated only by a few molecular tweaks here and there. When the differences in non-coding DNA are taken into account, that difference rises to 4 or 5 percent. Chimps and humans don't even have the same number of chromosomes (48 for chimps vs. 46 for humans).

"We have to get away from this vastly oversold notion that we're the same," Cohen said. "Let's grow up, and let's stop that."

The differences range from physiological factors (chimps don't suffer from the kinds of heart disease and cancer that afflict humans), to behaviors (humans can swim, chimps generally can't), to cognitive abilities. For years, primatologists have debated whether chimps can use language, or teach concepts to each other, or do math, or identify with the plight of someone else — but there's no debate that humans put chimps to shame in those departments.

Cohen thinks there are several factors behind our desire to think that chimps are like us:

• Save the chimps: Conservationists may emphasize the similarities as a strategy to build up support for preserving wild chimpanzees in Africa, where they are an endangered species. "It works, because the public cares about chimps more than any other species," Cohen said. "But come on — we care about whales and elephants, and they don't look like us."
• Support for evolution: A long time ago, some Darwinists pointed to the similarities as evidence of evolution at work. But that argument may be counterproductive now, since it's clear that humans and chimps had common ancestors that didn't look or act like either species. Current evolutionary theory rests on a wide array of evidence, and not just on the human-chimp connection. "We don't need that argument any longer," Cohen said.
• We are not alone: "We're fascinated by the notion that we can communicate with species on other planets, that the universe isn't as lonely as it appears to be," Cohen observed. "If we could somehow have a chimp that was more like us, it would satisfy this deep science-fiction desire for communication with others, and make us feel less lonely. But it's a fantasy."

So unless you have 5 million years to spare, don't expect to take over the world by breeding an army of intelligent chimps. An army of intelligent robots is a more likely option. However, "Rise of the Planet of the Apes" does provide an opportunity for some serious reflection of the wholly human variety. Among the issues to reflect upon are these:

• Humanized species: It's becoming more common to transplant our genes into other species — for instance, the mice who were given a "humanized" version of the gene linked to language and speech. Humanized mice are even being created in college science projects. The trend has rung alarm bells at the British Academy of Medical Sciences, which is calling for a ban on experiments that might give human characteristics to other primates. (Note the "Planet of the Apes" angle in this video.) Last year, U.S. bioethicists made a similar call for regulation, saying that it would be "ethically unacceptable" to conduct humanization research with apes. (Here's a scary sentence: "Imagine the life of the transgenic chimpanzee that, while no more self-aware than other chimps, is hairless, walks erect, lacks long canine teeth, or vocalizes like a human.")
• 'Species-ism' at work: Even if chimpanzees are not as humanlike as some people may think, should they and other great apes be given special treatment? European regulators think so: They have ruled out most biomedical research on apes, while allowing experimentation on monkeys, our more distant relatives on the primate family tree. A similar debate over invasive chimpanzee research is simmering in the United States. Cohen says "species-ism" is a natural human tendency. We value mice over mosquitoes, monkeys over mice, and men over monkeys. "We do feel closer to some species than others, and we feel closest to the great apes because we're in the same family," he said. "But that doesn't mean tha we're them and they're us."
• Defining humanness: Some may question whether chimps should qualify as "persons" under the law, but no one would confuse a chimp with a human. In fact, Cohen argues that one of the main reasons to study chimpanzees is to track down the roots of the differences between our species and our closest relatives in the animal kingdom. "It clarifies what a human is, and what it means," he said.

One of the closing lines of Cohen's book resonates particularly strongly as "Rise of the Planet of the Apes" goes into its big opening weekend: "Humans will determine the fate of chimpanzees. Chimpanzees of course will have no say in the fate of humans. And that may be the single most conspicuous difference between the two species."

Do you agree? Feel free to weigh in with your comment below. And, oh, by the way: Let me know how you liked the movie.

Extra credit: If you're looking for a blockbuster movie that's on firmer (but equally scary) scientific ground, Cohen suggests keeping an eye out for "Contagion," a meticulously researched action-thriller that's due to debut next month. Looks like it has a dynamite cast — Matt Damon, Gwyneth Paltrow, Jude Law, Kate Winslet, to name a few — but the trailer is making me feel a little skittish about putting my fingers on the computer keyboard.

More about chimpanzees and humans:

• Did chimp and human ancestors interbreed?
• Dogs (not chimps) are most like humans now
• How humans got big brains and barbless penises
• Give a chimpanzee a video game and ...
• Search for chimpanzees on msnbc.com

Connect with the Cosmic Log community by "liking" the log's Facebook page or following @b0yle on Twitter. You can also add me to your Google+ circle, and check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.