Mark Pine

Less than half of Americans accept as fact that humans descended from ape-like primates, according to a survey by the National Science Foundation in 2006. People like me wonder about these deniers of science. How do their minds work?

Not only does evolution seem self-evident, since many animals of different species are so much alike—think of wolves and dogs, tigers and cats, as well as chimps and humans—but today we understand DNA and mutations, concepts that help to explain it. So, how is it possible for reasonable people to reject evolution?

Nevertheless, Americans hold an overwhelmingly positive attitude toward science. According to a Pew Survey last year, 84% of us see science as having a positive effect on society. This seems paradoxical. What mental mechanisms would allow so many people to deny a core scientific theory like evolution and at the same time see science as doing much good?

Yesterday, science journalist Jay Ingram, suggested one explanation in a Scientific American podcast. Notwithstanding the well-known aphorism that you can choose your own opinions but you can’t choose your own facts, he proposed that many people actually do both.

His explanation came up in connection with the climate change debate, in order to explain why many people refuse to accept any human contribution to the phenomenon. Ingram suggested that people pay attention mostly to facts that support their beliefs but usually ignore others that don’t. Conversely they particularly scrutinize and find fault with facts that contradict their beliefs, while they accept uncritically those that confirm them.

Ingram’s proposal is supported by Pew results showing the most religious people, who attend religious services weekly or more often, question evolution more frequently than others (49% do). And conservative Republicans have the lowest rate of accepting that human activity increases global warming (21% do).

I suspect, however, that there is another reason, perhaps as significant. It is clearly expressed in an old rock ‘n’ roll song:

Don’t know much about history
Don’t know much biology
Don’t know much about a science book
Don’t know much about the french I took
But I do know that I love you
And I know that if you love me too
What a wonderful world this would be

Science and scientific knowledge are hard work, and learning them causes mental and emotional pain, even anguish at times. When you are in high school—the age group for whom Sam Cooke sung his 1958 tune—there’s little immediate payoff for making the intellectual effort to master the subjects, particularly during years when instinctual drives dominate the mind.

Many Americans who passed on science during their educational years cannot now understand its logic and reason. A significant number of us, I suspect, prefer to reject science in favor of religion or other sources of opinion, whose reasons we are able to comprehend. For this group, it’s not a matter of choosing your own facts, but rather allowing ourselves to live in the absence of facts. Ignorance—for a certain group of Americans, perhaps a substantial number of us—is indeed bliss.

In Mary Shelley’s novel, Dr. Frankenstein is the creator of the monster, not the monster himself. And in the article last week in Scientific American, it is not a single scientist working alone who creates new life (actually that has already been done by Craig Venter), but a consortium of academic institutions launched earlier this year that is working together to assemble standardized parts of living organisms.

The BioFab is a “DNA factory” located within Lawrence Berkeley National Laboratory’s Joint BioEnergy Institute in Emeryville, CA. It is funded by the the laboratory, the National Science Foundation and the BioBricks Foundation. Run by scientists from UC Berkeley and Stanford, it’s website explains that BioFab will “produce broadly useful collections of standard biological parts that can be made freely available to both academic and commercial users.” The name BioFab was inspired by the Fab established by the semiconductor industry to design and manufacture custom chips. According to the BioBricks Foundation,

Using … standard biological parts, a synthetic biologist or biological engineer can already, to some extent, program living organisms in the same way a computer scientist can program a computer.

Gene promoters and ribosome binding sites are two examples of the kind of part that BioFab will design, manufacture, and stock. The former are sequences of nucleotides adjacent to a gene, where RNA polymerase attaches and initiates translation of the DNA into the corresponding messenger RNA. The latter are short sequences of nucleotides of messenger RNA that bind to ribosomes, the catalytic sites where proteins are synthesized by stringing together amino acids, according to the instructions specified in the message.

All proteins have their own sets of genes, promoters, ribosome binding sites, and other similar elements in the DNA and RNA molecules that encode them. BioFab will attempt to catalog and stock as many of these elements as it can.

In drawing a connection to the Frankenstein novel at the beginning this post, I wanted to point to the issues it raised. Just as Dr. Frankenstein failed to foresee the tragic consequences of his creative work, I find nothing on the BioFab or BioBrick websites that consider the potential negative consequences of making life parts available for order.

I do not disagree that this work should be done. But history shows that the Frankenstein-like “monsters” can and sometimes actually do arise from scientific work. Just as the monster escaped from his creator’s lab and roamed the countryside committing murders, inevitably life actually created in scientific laboratories WILL escape from those facilities and WILL in some instances inflict harm on the planet’s natural life.

If we are to do this work (and I think we should), then our government and others of the world should license and regulate the facilities in which it is done and require effective containment of the new life forms that are created.

New life forms should not be allowed to escape into the environment or to be released intentionally. Once free, life multiplies and mutates. And it is possible that some liberated creations— and their genes—would not die off but persist and spread uncontrollably.

Our hi-tech civilization makes use of tens of thousands of chemicals, most of which haven’t been tested for noxious effects. Inhaled, ingested, or in contact with skin, the substances sometimes cause respiratory disease, damage the nervous system, interfere with hormones, or trigger cancer. In a Scientific American article Tuesday, Paul Blanc, a professor of occupational and environmental medicine at U.C. Berkeley, answered questions about toxic chemicals.

People may get exposed to harmful chemicals in common consumer products, Blanc said. He mentioned waterproofing sprays used on shoes and leather, as one good example. The aerosols contain fluoropolymers that can cause severe lung damage.

I used one such product two days ago, Kiwi Protect-all from Sara Lee Household and Body Care. At that time, I had no idea that severe lung damage could result from ingredients in the can. This morning, I checked the label, which says only that it contains “petroleum distillates,” hardly informative. I also went to the the Kiwi website, but that divulges even less info. However, my call to a telephone number on the can to contact for “questions” confirmed that Protect-all does contain fluoropolymers.

When I applied the spray to new running shoes, I did take the precaution of using it in a screened porch with lots of airflow. Still, if I had known, I would have taken more care, like holding my breath while spraying and leaving the porch before taking a breath.

What can be done to control the use of toxic substances and increase the information available to consumers?

The Congress is now considering new legislation to overhaul the decades old Toxic Substances Control Act. It is “an antiquated law that in its current state, leaves Americans at risk of exposure to toxic chemicals,” according to Sen. Frank Lautenberg (D-NJ), who introduced the new bill, the Safe Chemicals Act of 2010. He explains on his website that the Environmental Protection Agency “does not have the tools to act on dangerous chemicals and the chemical industry has asked for stronger laws so that their customers are assured their products are safe.” The description of the bill says:

The “Safe Chemicals Act of 2010” requires safety testing of all industrial chemicals, and puts the burden on industry to prove that chemicals are safe in order stay on the market. Under current policy, the EPA can only call for safety testing after evidence surfaces demonstrating a chemical is dangerous. As a result, EPA has been able to require testing for just 200 of the more than 80,000 chemicals currently registered in the United States and has been able to ban only five dangerous substances. The new legislation will give EPA more power to regulate the use of dangerous chemicals and require manufacturers to submit information proving the safety of every chemical in production and any new chemical seeking to enter the market.

Even if the bill were to become law soon (probably unlikely in this election year), the U.S. would be catching up to Europe. In 2007, the EU’s European Chemical Agency (ECHA) inaugurated REACH, a program for “Registration, Evaluation, Authorisation and Restriction of Chemicals.”

According to the ECHA website, REACH

applies to all chemicals: not only chemicals used in industrial processes but also in our day-to-day life, for example in cleaning products, paints as well as in articles such as clothes, furniture and electrical appliances. … All manufacturers and importers of chemicals must identify and manage risks linked to the substances they manufacture and market.

Concern about thousands of potentially harmful chemicals in consumer products growing in this country, too. In May, Nicholas Kristof, the NY Times columnist wrote about a new report from the President’s Cancer Panel, which warns that “our lackadaisical approach to regulation may have far-reaching consequences for our health.”

Perhaps something will get done, and before long, I won’t be surprised by a news article informing me that a consumer product I used just a couple days previously might possibly cause me to suffer from a severe disease.

This year Washington, DC, experienced the hottest June on record, and the records go back to 1872. Yet, when it comes to taking action to reduce the CO₂ emissions that are contributing to global warming, the senators in the city are frozen in inaction. That’s the pessimistic opinion today of David Leonhardt, a business columnist of the NY Times. He writes that the 60 votes needed to pass climate legislation are not to be had at the present time. Leonhardt discusses the futility of trying to pass a bill to put a price on carbon, like cap-and-trade legislation, and he asks whether it makes sense for now just to try to legislate some rules, similar to vehicle mileage standards, that would to curb fossil fuel consumption.

What can be done and how it might be accomplished was also the subject of a Scientific American article last week. It depends, the piece suggested, on how much global warming we Americans are willing to accept. The article reviewed a new report of the National Research Council on the impacts of every degree Celsius of global temperature increase. These are a few of them:

• A 5 to 15 percent lower yield for some crops, including corn in Africa and the U.S., and wheat in India
• A 3 to 10 percent increase in heavy rainfall globally
• A 5 to 10 percent drop in rainfall in southwestern North America, southern Africa and the Mediterranean
• A 5 to 10 percent change (increases in some regions, decreases in others) in stream flow in many river basins globally
• A 15 to 25 percent decrease in the extent of Arctic Ocean sea ice

The report presents the hazards in terms of temperature changes rather than atmospheric CO₂ levels. Perhaps doing that might make the consequences easier for the public and the senators to grasp and evaluate. The report’s authors believe that doing so removes some of the uncertainty clouding the debate. Whatever the cause of the warming, the report indicates, a 3-degree increase in global average temperature means arctic ice is gone.

The SciAm article also makes the essential point that action on climate in the Congress and the country as a whole depends on the attitude of the public toward the issue.

In that connection, researchers at the Center for Climate Change Communication at George Mason University in Fairfax, VA, may have discovered a way to boost support for taking action. The scientists interviewed 70 volunteers, who each read an essay on climate change as a health issue.

The study included approximately equal numbers of people who fell into each of six attitude groups in regard to the global warming debate. Three groups accepted that it is occurring—those who felt “alarmed,” “concerned,” or “cautious” about the consequences, and three other groups had doubts—those who felt “disengaged,” “doubtful,” or “dismissive” toward the issue. The scientists interviewed each person after the reading and assessed their opinions, positive or negative, toward the essay as a whole and each of 18 sentences.

Remarkably many of the volunteers in every group “reacted positively to the information.” For example, 44% of the disengaged subjects “indicated that the essay reflected their personal point of view, was informative or thought-provoking, or offered valuable prescriptive information on how to take action relative to the climate problem.” But even more surprising was the response to the four sentences in the essay that focused on the benefits to health of curbing climate change. Most of the volunteers—both the acceptors and the doubters—reacted positively to this information. In contrast, the doubters reacted negatively to 14 other sentences in the essay, including seven that described threats to health of continuing climate change (as opposed to the benefits of stopping it), five introductory sentences and two concluding ones.

The research points to an impediment that may be interfering with building support for action on climate change. The debate so far has mostly been presented in rather abstract terms, like emissions and concentrations of CO₂ or conditions distant in place and time, like the melting of arctic ice or the expansion of deserts. Discussing the issue that way makes the consequences seem far removed. It would be better, perhaps, to talk in personal terms, like the potential benefits to people’s health. That might help to bring the issue home.

That’s the question asked in the headline of an article in last month’s Scientific American. The author, Craig Callender, is a philosophy professor at UCSD, and it’s a question only a philosopher or a physicist could ask.

Most of us mortals know time exists. Is it real that my skin wrinkles and my hair turns gray? Is it an illusion that my muscles lose mass and my stature loses height? I wish those things were just figments of imagination. (The question whether time really exists reminds me of the question scientists sometimes ask whether consciousness really exists.)

But the question about time arises in cosmological circles primarily because of Einstein and his Theory of Relativity, which undermined the concept of a clockwork universe envisioned by Newton. Einstein turned time into a kind of space by describing a four-dimensional spacetime—a network spanning the universe, which can fold, stretch, twist and tie itself in knots. In such a universe, the future shifts with respect to the past and the concept of the time when something happens becomes…well…relative.

But in contrast to relativity theory, Callender says, time is real and robust in quantum mechanics. He writes:

The full description of an object is given by a mathematical function called the quantum state. This state evolves continuously in time. Using it, physicists are able to calculate probabilities of any experimental outcome at any time.

For QM to make sense, there must be a past in which the quantum state evolves and a future for it to predict.

Physicists have been trying to bridge the contradictions between relativity and quantum mechanics for decades, and one of the main issues is the concept of time, Callender says. One thing, however, that does not seem different in the two theories’ notions of time is the idea that events occur in an order.

In the universe, events occur in sequence. Some events occur before others and others occur afterward. Some things happen earlier and others happen later. Indeed, both theories use sequences of earlier events to predict later ones.

It doesn’t seem to be required by either theory that the amount of time or interval of spacetime between events necessarily be the same for all observers. Events can move faster or slower depending on the situation of the observer (that sort of thing happens to me all the time). But the order in which things happen does not change.

This is where the Second Law of Thermodynamics—entropy—enters the picture, a topic that Callender did not discuss. For the universe as a whole, the sequence of events must be ordered so that the entropy of the universe increases. Only certain sequences are allowed by the Second Law.

I wonder about this: In QM, the complete descriptions of the universe and its various parts are given by quantum states, which evolve in time. According to the classical Copenhagen interpretation of QM, at moments in time, the quantum states are realized in actual material reality, through a process called “collapse” in which the probabilities of the states are transformed briefly into certainties. In other versions of QM, also, transformations of quantum states and their probabilities into actual realities must also somehow occur, if the notion of reality is to mean anything. The sequences of transformations of quantum states into actual reality is what creates the real universe and all its real parts.

These sequences of transformations implied in QM seem naturally to give an order to events that could structure time and satisfy the requirements of that theory. The Second Law of Thermodynamics would allow only some sequences and not others. And the amount of time between transformations (or the interval of spacetime between them) would be determined by light (photons) traveling from one to the next, which would satisfy the requirements of the Theory of Relativity.

We should not be surprised that our ability to make quantitative judgments is inborn and operational from the beginning of life. Number and size are fundamental aspects of our world. Still, it causes us to wonder and marvel when psychological experiments show that infants can make quantitative comparisons even before they can use language.

Researchers at Emory University in Atlanta tested nine-month-old infants using a technique that followed their gaze. The methodology assumes that the longer babies fixate on an object or scene, the more information processing is going on in their brains. For example, when babies see something novel or unexpected, they tend to gaze at it longer so that they can assimilate the new information. The research was reported Tuesday in ScienceDaily.

In the experiments, the babies watched computer screens, on which various objects appeared colored with black and white stripes or black dots on white background. The scientists trained their young subjects to expect more objects or larger objects with one of the patterns than the other, and then they would violate the “rule” that they had taught the babies to expect. When the number or size of the images on the computer failed to correspond to the expected pattern, the babies would look longer, indicating that they were surprised and were taking in the new information. That indicated, in turn, that the infants had formed mental rules about the relationships of size and number to color pattern.

We often assume that the higher cognitive abilities, including quantitative judgment, are human traits that depend on our acquisition of language. But much research suggests this may not be so. At nine months of age, the babies in the Emory University study were too young to understand words or speak. But evidently they already had the ability to compare numbers and sizes.

Moreover, other research has shown that many animals without human speech can also make quantitative judgments. In an article last fall in Scientific American, it was reported that monkeys and birds (even newly-hatched chickens) demonstrated quantitative abilities in experimental situations. In 2008, scientists in Italy showed that fish of a certain species could count to 4.

Human cognitive abilities are clearly special and unique, but it appears to be true that our aptitudes are not singular in kind but rather in extent. Our abilities apparently evolved with the evolution of animals, and many animals demonstrate human-like cognitive abilities at much more rudimentary levels of functioning. More information on scientific work on animal cognitive abilities, particularly language capacities, may be found at the website of the Max Planck Institute for Evolutionary Anthropology.

I’ve just about given up eating at restaurants. Perhaps on very special occasions—my children come to town, I make a long trip—or when for some reason there’s no choice, I dine out. But most often when I think about what I’ll be eating at most eateries, I sigh and decide to skip it.

It’s not the quality of the food, per se, or worries about germs, it’s the sugar, fat and salt. There’s just about nothing to order at most restaurants that isn’t loaded with sugar, fat and salt.

On Tuesday, the Center for Science in the Public Interest, the organization that publishes Nutrition Action Healthletter, posted a story on the mind-boggling excess of some restaurant-chain meals:

• A breakfast of Bob Evans Cinnamon Cream Stacked and Stuffed Hotcakes? 1380 cal and 34 g of fat. If that ever made sense, it’s was for farmers going out to plow their fields with oxen.
• A dinner of P. F. Chang’s Double Pan Fried Noodles Combo? 1820 cal and 7690 mg of salt. Go ahead and raise your BP by 10-20 mmHg.
• A desert of the Cheesecake Factory Chocolate Tower Truffle Cake? 1670 cal and 48 g of fat. Enough to fuel a 30-mile bike ride.

These are extreme examples, but most restaurant food suffers from the same mix of fat and salt and sugar, particularly at chain restaurants. David Kessler, former Commissioner of the FDA and a pediatrician on the faculty of UCSF, explained why the eating places do it. In the book The End of Overeating, he wrote about the research food companies have done on maximizing the taste, palatability, and appetite stimulating properties of food. They have discovered how to blend sugar, fat and salt into foods to produce concoctions that are so extremely rewarding to eat that instead of being satisfied by eating them, we are stimulated to want to eat more and more. Unfortunately, the food that does that is overloaded with unhealthy calories.

Most restaurants, particularly the chains that depend on keeping customers coming back, have applied the results of the food research and adopted the same food-company philosophy of leaving us wanting to eat more.

About five years ago, when I passed age 60, I decided I could no longer ignore my excess weight. I wished to live a vigorous old age, so I had to lose the fat or lose my health. I’ve since kept close track of what I consume and lost 40 lbs.

Today, I’m so conscious of the calories, fat, sugar and salt in what I eat, that I can’t seriously consider eating at restaurants more often a few times a year.

Researchers in Sweden and the U.S. asserted last week that creative thought and schizophrenic thinking share similar neurophysiologic mechanisms involving dopamine neurotransmission. Their investigation connected “divergent thinking,” a style of thinking involving unusual or bizarre associations, to reduced density of dopamine receptors in the thalamus, a part the brain that relays neuronal impulses from one brain region to another. The scientists also pointed out that low dopamine receptor density is associated with a particular genetic variant, that might be more common among both creative individuals and the mentally ill. The scientists did their work at the Karolinska Institute in Stockholm and the National Institute of Neurological Disorders and Stroke in Bethesda, Md.

Dopamine is a neurotransmitter, a substance that is released into synapses between neurons in the process of transmission of neuronal impulses. It is one of many brain neurotransmitters, and it has long been connected with schizophrenia. Anti-schizophrenic drugs are known to work, in part, by occupying dopamine receptors and blocking neurotransmission.

According to a report in ScienceDaily, Dr. Frederick Ullén, one of the researchers, discussed the D2 receptor, they type of dopamine receptor the scientists investigated. He explained,

“Fewer D2 receptors in the thalamus probably means a lower degree of signal filtering, and thus a higher flow of information from the thalamus,” [and] this could a possible mechanism behind the ability of healthy highly creative people to see numerous uncommon connections in a problem-solving situation and the bizarre associations found in the mentally ill.

If increased information flow underlies both creativity and schizophrenia, that could explain why creative people come quickly to unusual ideas and why anti-schizophrenic drugs would reduce bizarre thinking and the manifestations of mental illness.

Genius and madness have long been connected. The Independent, the British newspaper, noted that geniuses including the composer Schumann, the playwright Strindberg, the author Kafka and the philosopher Wittgenstein were schizotypal personalities.

Last year, the magazine Psychology Today published an article on schizophrenic thought and genius, which suggested that the reduction of a neurophysiologic function called “latent inhibition” might diminish filtering of emotions and sensations. Reduced latent inhibition is known to be associated with schizophrenia, the article reported, but it might also be beneficial for creativity. The condition sounds very similar to the low signal filtering in the thalamus, which the researchers at Karolinska and the NIH investigated and reported on.

The answer is not really, not as the media hype has portrayed it.

Although he has accomplished a marvelous technical feat of genetic engineering, what Venter did is to copy and synthesize the genome of a naturally occurring form of bacteria. Then he modified some portions of it, and inserted it into a hollow cell—a cell from which the genome had been removed—of a closely related bacterium.

This morning, the NY Times summarized Venter’s achievement this way: “Dr. Venter copied the DNA from one species of bacteria and inserted it into another. The second bacteria made all the proteins and organelles in the so-called ‘synthetic cell,’ by following the specifications implicit in the structure of the inserted DNA.”

A report in Science described the work as follows:

…the stepwise creation of a bacterial chromosome and the successful transfer of it into a bacterium, where it replaced the native DNA. Powered by the synthetic genome, that microbial cell began replicating and making a new set of proteins. The synthetic genome created by Venter’s team is almost identical to that of a natural bacterium.

In 1995, according to the Science article, Venter and his crew initiated a project to identify a minimal genome of a free-living organism. To do so, they investigated a group of bacterial called Mycoplasma, which are very simple organisms. In intermediate steps toward their goal, in 2007 and 2008, they succeeded in transfering the genome from one microbe into another and synthesizing an artificial chromosome matching that of M. genitalium, which has the shortest genome known.

To prove that he had identified a minimal, life-sustaining gene set, in 2009 Venter extracted the DNA from M. mycoides bacteria, modified it, and reinserted it into a hollow cell of M. capriolum, a species closely related to mycoides. In the work reported yesterday, Venter had another company synthesize the mycoides DNA from scratch in 1000 pieces. Then he and his staff pieced the DNA together and inserted it into another hollow mycoides cell. It took several tries to get it right, with the result that the new mycoides cell has survived, reproduced, and formed a colony of M. mycoides bacteria, all having the artificial genome.

The stories make clear that there are some extremely important things that Venter did not do. To my mind, the most critical is that he simply copied the genome of an existing living organism. He has not determined the functions of the individual genes nor how they work together. Although he has created an artificial genome that works in a pre-existing cell of the same type, he does not understand why it works. And he lacks the information necessary to build a new life form by selecting from a kit of individual genes, as though, to use a metaphor, he were building a new structure from Lego blocks.

Moreover, almost as significantly, he did not synthesize an artificial cellular environment—the hollow cell that hosted the artificial genome and enabled it to work and reproduce. There is no reason to believe, on the basis of the reports, that he has determined which components of the hollow cell are necessary or how to create an artificial cell that would allow a synthetic genome to function.

Nevertheless, Venter has indeed built a form of life that the earth has never seen before. And his work is an important step on the way to true creation of life. However, other genetic engineers have done the same kind of thing, albeit by inserting or deleting only a few genes.

As with all forms of genetic engineering that creates new life, I believe the main potential ethical problem with doing this kind of work concerns the possibility of interfering with the operation of the biosphere—the interrelated web of life of our planet—should the artificial organism be released purposely or accidentally onto the earth.

In my view, it is fine—desirable, in fact—to do this sort of work in the laboratory, as part of scientific research to understand the basis of life. It may also be a good to synthesize new life forms capable of benefitting life on earth, including human life.

But in my view, it is not ethical or wise to release newly synthesized forms of life free into the environment, to do and multiply as they will. If Venter were to release his new bacterium into the biosphere, it might well succeed and reproduce. But it would not stay where he put it and the remain in the form it is for long. It would move, swap genes with other organisms, evolve, and develop along an evolutionary path that no natural organism would have traveled.

Humans do not know enough about the biosphere to know what we do when we introduce gene-engineered organisms free in the world. It’s true that for thousands of years humans have used breeding in farming to modify natural organisms and create new ones. But those newly bred organisms incorporated genes closely related to those they already possessed. GE, however, allows the insertion of extremely different genes from sources unrelated and far-removed.

The relationship of genetic engineering to breeding technology is like the relationship of the jet and auto to that of the horse and buggy. And, the potential effects on the environment of GE are also like that of modern transportation technology in comparison to animal-based transportation—perhaps even like nuclear bombs in comparison to the fire-crackers.

That touchy GEICO caveman—he needn’t feel so affronted. It turns out that for many modern humans, we probably have a little caveman in us, genetically speaking.

Apparently, the ancestors of modern humans of Asia and Europe (my ancestors among them) and Neandertals may have fooled around in the limestone caves of Mt. Carmel, Israel—or perhaps more likely on the nearby Mediterranean shores. That’s one possible interpretation of the conclusions gained from the sequencing the Neandertal genome, which was reported in Science on Friday.

Fossils of Neandertals in Europe show that the species lived there from 400,000 to 30,000 years ago and then died out. Near the end of that time, however, they extended their range into Asia and into the Middle East, where they may have come into contact with modern humans after 80,000 years ago. There the two species may have remained in proximity for 50,000 years. Yet many anthropologists did not believe they interbred until now.

As explained in a news article in the same issue of Science, a team led by paleogeneticist Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology in Leipzig sequenced the DNA extracted from the fossil bones of three female Neandertals who lived in Croatia around 40,000 years ago. Then they compared the sequence obtained from a composite genome sequence of the three Neandertal individuals’ DNA with the genome sequences of present-day humans from around the world—France, southern Africa, West Africa, China, and New Guinea.

The nucleic acid of modern humans and Neandertal DNA is 99.84% identical, but scientists identified regions of the DNA of the present-day humans that is different from the Neandertal. The discovered that differences occurred in genes involved with skin, metabolism, skeleton, and cognitive development, although the precise function of these genes is not known.

The scientists also looked for genetic differences that take the form of differences in single base pairs of DNA (called single nucleotide polymorphisms, SNPs). They compared the composite Neandertal genome and those of 8 present-day humans (2 European Americans, 2 East Asians, and 4 West Africans).

If gene exchanges between modern humans and Neandertals stopped before modern human populations separated around the globe, then the Neandertal genome should match all the 8 present-day human genomes equally often. But if some of the present-day human genomes match the Neandertal more than others, then that that would indicate that the populations of humans with more matching genomes continued to exchange genes with Neandertals after modern human populations spread out.

The comparison showed that the matching is greater between the Neandertal SNPs and those of the 4 European and Asian present-day humans than for the 4 Africans. Using a statistic D that measures such genetic differences, the scientists found that D remained within 1.2 standard deviations of 0 (no divergence) when Asian, European, and Neandertal genomes were included in the comparison. But D fell beyond 11 standard deviations from 0 when African genomes replaced either Asian or European genomes in the comparison.

Where and when might this gene swapping have occurred? According to the news article, one possibility is after 80,000 BCE, after some populations of modern humans left Africa, in the region of the limestone ridge of Mt. Carmel. Fossils indicate that modern humans and Neandertals inhabited caves in the area during tens of thousands of years, and it’s conceivable that the two species came in contact.

Actually, I’ve always thought that Europeans look more like Neandertals than Africans do. But for some people who hope to justify notions of European superiority, it might be a difficult idea to accept. Apparently, Europeans are more genetically like Neandertals—the popular notion of the cavemen—than are Africans.