livearevolution

By ROBERT LEE HOTZ

Christine Verna Max Planck Institute-EVA

A close-up of the bone Vindija 33.16 from Vindija cave, Croatia.

The burly Ice Age hunters known as Neanderthals, a long-extinct species, survive today in the genes of almost everyone outside Africa, according to an international research team who offer the first molecular evidence that early humans mated and produced children in liaisons with Neanderthals.

In a significant advance, the researchers mapped most of the Neanderthal genome—the first time that the heredity of such an ancient human species has been reliably reconstructed. The researchers, able for the first time to compare the relatively complete genetic coding of modern and prehistoric human species, found the Neanderthal legacy accounts for up to 4% of the human genome among people in much of the world today.

By comparing the Neanderthal genetic information to the modern human genome, the scientists were able to home in on hints of subtle differences between the ancient and modern DNA affecting skin, stature, fertility and brain power that may have given Homo sapiens an edge over their predecessors.

Intertwined

Research suggests humans, Neanderthals interbred.

"It is tantalizing to think that the Neanderthal is not totally extinct," said geneticist Svante Pääbo at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who pioneered the $3.8 million research project. "A bit of them lives on in us today."

The discovery is the climax of a vociferous scholarly debate over the fate of the Neanderthals, a big-brained and barrel-chested group who roamed Europe, Russia and the Middle East between 400,000 years and 30,000 years ago, overlapping in many areas with the direct ancestors of modern humankind. Their remains were the first human-like fossils ever found. For more than 150 years, most scientists have considered the species one of evolution's failed experiments, one that died out—or was killed off—when it could not compete with more advanced Homo sapiens.

Previous fossil DNA studies, based on more fragmentary genetic samples, showed no evidence that Neanderthals left any traces in the modern human genome, as the complete set of an organism's genetic inheritance is called.

The new findings arise from a technological revolution in the study of ancient biology. Researchers used high-speed, genome-sequencing machines from 454 Life Sciences and Illumina Inc., along with powerful computational statistical tools, gene-splicing enzymes and microarray analysis techniques, to resurrect the information entombed in fossil DNA.

For their analysis, Dr. Pääbo and his colleagues extracted DNA mostly from the fossil remains of three Neanderthal women who lived and died in Croatia between 38,000 and 45,000 years ago. From thimblefuls of powdered bone, the researchers pieced together about three billion base pairs of DNA, covering about two-thirds of the Neanderthal genome. The researchers checked those samples against fragments of genetic code extracted from three other Neanderthal specimens.

Max-Planck-Institute EVA

For their DNA study, researchers used thimblefuls of powdered bone extracted from these three Neanderthal bones found in the Vindija cave.

"It is a tour de force to get a genome's worth," said genetic database expert Ewan Birney at the European Bioinformatics Institute in Cambridge, England.

In research published Thursday in Science, the researchers compared the Neanderthal DNA to the genomes drawn from five people from around the world: a San tribesman from South Africa; a Yoruba from West Africa; a Han Chinese; a West European; and a Pacific islander from Papua, New Guinea. They also checked it against the recently published genome of bio-entrepreneur Craig Venter. Traces of Neanderthal heredity turned up in all but the two African representatives.

"We do not find any evidence of Neanderthal gene flow into Africans," said population geneticist David Reich at Harvard University Medical School, who helped analyze the Neanderthal genome. "What we find is shared equally by Europeans, East Asians and Papua, New Guineans."

From that pattern, the researchers deduced that prehistoric humans encountered their Neanderthal mates in the Middle East as small human bands first migrated out of their African homeland. There may have just been a few encounters. "A little interbreeding would have spread those genes far and wide," said British anthropologist Chris Stringer at London's Natural History Museum.

Johannes Krause, Max Planck Institute-EVA

The Vindija cave in Croatia, where the Neanderthal bones -- remains of three women who lived between 38,000 and 45,000 years ago -- were found.

Based on these findings, several anthropologists questioned whether Neanderthals should continue to be considered a separate species. Typically, when different species mate, they don't produce fertile offspring. "I really think when you get up to 2%-to-5% genetic overlap, it is probably not wise to think of these as a separate species," said anthropologist Fred Smith at Illinois State University who studies Neanderthals.

In the long run, the researchers hope that they can use the Neanderthal genome as a yardstick against which they can measure evolutionary changes in more modern human genes that may have contributed to the success of Homo sapiens. By comparing and contrasting the modern human genome to both the Neanderthal and even more primitive chimpanzee genetic data, researchers hope to uncover uniquely human adaptations. Already, they have drawn up a list of 212 variations that appear to have been favored during modern human evolution, compared with the Neanderthals. Those include genes involved in energy metabolism, sperm motility, the development of the rib cage, collar bone and cranium, as well as genes that appear to be involved in cognition.

"This opens the way to studying genetic differences that make humans human," said ancient DNA specialist Alan Cooper at the University of Adelaide.

The new research is buttressed by an independent, unpublished survey of modern human diversity, involving DNA markers covering 100 population groups world-wide, which also offers evidence of ancient interbreeding between Homo sapiens and earlier archaic human species.

Evolutionary anthropologist Jeff Long at the University of New Mexico in Albuquerque presented the work at a science conference last month. "We felt you had to introduce some archaic admixture to explain the diversity of modern populations," Dr. Long said.

Science/AAAS

Researchers checked the DNA of the Croatia bones against fragments of genetic code extracted from specimens from three other locations. Numbers on the map are the approximate dates of the bones in years before present.

Despite its recent advances, the field of molecular anthropology is treacherous terrain. Bones are easily sullied as they decompose. Microbes so thoroughly infiltrated the Neanderthal bones that almost 99% of the DNA the researchers found actually belonged to bacteria and had to be painstakingly excluded. They also can be easily contaminated by modern human DNA when they are excavated and handled in the laboratory.

"By touching the bone, you leave more DNA on its surface than actually is in the bone itself," said geneticist Johannes Krause at the Max Planck Institute, who worked on the Neanderthal specimens. "That is one of the biggest risks we have."

Indeed, Dr. Pääbo and his colleagues were publicly embarrassed when an earlier analysis of Neanderthal DNA turned out to be thoroughly contaminated by modern human genes from lab workers. To avoid such errors in the new study, they tagged each Neanderthal DNA strand with a unique molecular bar-code, to distinguish it biochemically from any extraneous genetic material.

"Their laboratory work is impeccable," said molecular anthropologist Todd Disotell at New York University, who studied the findings but was not involved in the project. "I am very confident their data is bon fide."

love science!

Why don't I have a girlfriend?

This is a question that practically every male has asked himself at one point or another in his life. Unfortunately, there is rarely a hard and fast answer to the query. Many men try to reason their way through the dilemma nonetheless, often reaching a series of ridiculous explanations, each more self-deprecating than the last: "Is it because I'm too shy, and not aggressive enough? Is it my opening lines? Am I a boring person? Am I too fat or too thin? Or am I simply ugly and completely unattractive to women?" When all other plausible explanations have been discounted, most fall back on the time-honoured conclusion that "there must be Something Wrong™ with me" before resigning themselves to lives of perpetual chastity.^[2]

Not the author, though. I, for one, refuse to spend my life brooding over my lack of luck with women. While I'll be the first to admit that my chances of ever entering into a meaningful relationship with someone special are practically non-existent, I staunchly refuse to admit that it has anything to do with some inherent problem with me. Instead, I am convinced that the situation can be readily explained in purely scientific terms, using nothing more than demographics and some elementary statistical calculus.

Lest anyone suspect that my standards for women are too high, let me allay those fears by enumerating in advance my three criteria for the match. First, the potential girlfriend must be approximately my age—let's say 21 plus or minus three or four years. Second, the girl must be beautiful (and I use that term all-encompassingly to refer to both inner and outer beauty). Third, she must also be reasonably intelligent—she doesn't have to be Mensa material, but the ability to carry on a witty, insightful argument would be nice. So there they are—three simple demands, which I'm sure everyone will agree are anything but unreasonable.

That said, I now present my demonstration of why the probability of finding a suitable candidate fulfilling the three above-noted requirements is so small as to be practically impossible—in other words, why I will never have a girlfriend. I shall endeavour to make this proof as rigorous as the available data permits. And I should note, too, that there will be no statistical trickery involved here; I have cited all my sources and provided all relevant calculations^[3] in case anyone wishes to conduct their own independent review. Let's now take a look at the figures.

Number of people on Earth (in 1998): 5 592 830 000^[4]

We start with the largest demographic in which I am interested—namely, the population of this planet. That is not to say I'm against the idea of interstellar romance, of course; I just don't assess the prospect of finding myself a nice Altairian girl as statistically significant. Now anyway, the latest halfway-reliable figures we have for Earth's population come from the United States Census Bureau's 1999 World Population Profile (WP/98). Due presumably to the time involved in compiling and processing census statistics, said report's data is valid only as of 1998, so later on we'll be making some impromptu adjustments to bring the numbers up to date.

…who are female: 2 941 118 000^[5]

I'd've thought that, given the title of this essay, this criterion goes without saying. In case anyone missed it, though, I am looking for exclusively female companionship. Accordingly, roughly half of the Earth's population must be discounted. Sorry, guys.

…in "developed" countries: 605 601 000^[5]

We now further restrict the geographical area of interest to so-called "first-world countries". My reasons for doing so are not motivated out of contempt for those who are economically disadvantaged, but rather by simple probability. My chances of meeting a babe from Bhutan or a goddess from Ghana, either in person or on the Internet, are understandably low. In fact, I will most likely spend nearly my entire life living and working in North America, Europe, and Australia, so it is to these types of regions that the numbers have been narrowed.

…currently (in 2000) aged 18 to 25: 65 399 083^[4][5]

Being neither a pedophile nor a geriatrophile, I would like to restrict my search for love to those whose age is approximately equal to my own. This is where things get a bit tricky, for two reasons: first, the census data is nearly two years old, and second, the "population by age" tables in WP/98 are not separated into individual ages but are instead quantized into "15–19" (of whom there are 39 560 000) and "20–44" (population 215 073 000). Women aged 15 to 19 in 1998 will be aged 17 to 21 in 2000; in this group, I'm interested in dating those 18 or older, so, assuming the "15–19" girls' ages are uniformly distributed, we have

Similarly, of 1998's "20–44" category, there are now

females within my chosen age limit. The sum, 66 059 680, represents the total number of females aged 18 to 25 in developed countries in 2000. Unfortunately, roughly 1% of these girls will have died since the census was taken;^[6] thus, the true number of so-far eligible bachelorettes is 65 399 083.

…who are beautiful: 1 487 838

Personal attraction, both physically and personality-wise, is an important instigator of any relationship. Of course, beauty is a purely subjective trait whose interpretation may vary from person to person. Luckily it is not necessary for me to define beauty in this essay except to state that for any given beholder, it will probably be normally distributed amongst the population.^[7] Without going into the specifics of precisely which traits I admire, I will say that for a girl to be considered really beautiful to me, she should fall at least two standard deviations above the norm. From basic statistics theory, the area to the left of the normal curve at z = 2 is

and so it is this number with which we multiply our current population pool.

…and intelligent: 236 053

Again, intelligence can mean different things to different people, yet I am once more relieved of making any explanation by noting that it, like most other characteristics, has a notionally normal distribution across the population. Let's assume that I will settle for someone a mere one standard deviation above the normal; in that case, a further

of the population must be discounted.

…and not already committed: 118 027

I could find no hard statistics on the number of above-noted girls who are already married, engaged, or otherwise committed to a significant other, but informal observation and anecdotal evidence leads me to believe that the proportion is somewhere around 50%. (Fellow unattached males will no doubt have also noticed a preponderance of girls legitimately offering, "Sorry, I already have a boyfriend" as an excuse not to go on a date.) For reasons of morality (and perhaps too self-preservation), I'm not about to start hitting on girls who have husbands and boyfriends. Accordingly, that portion of the female population must also be considered off-limits.

…and also might like me: 18 726

Naturally, finding a suitable girl who I really like is no guarantee that she'll like me back. Assuming, as previously mentioned, that personal attractiveness is normally distributed, there is a mere 50% chance that any given female will consider me even marginally attractive. In practice, however, people are unlikely to consider pursuing a relationship with someone whose looks and personality just barely suffice. Let's make the rather conservative assumption, then, that a girl would go out with someone if and only if they were at least one standard deviation above her idea of average. In that case, referring to our previous calculation, only 15.8655% of females would consider someone with my physical characteristics and personality acceptable as a potential romantic partner.

Conclusion

It is here, at a pool of 18 726 acceptable females, that we end our statistical analysis. At first glance, a datable population of 18 726 may not seem like such a low number, but consider this: assuming I were to go on a blind date with a new girl about my age every week, I would have to date for 3493 weeks before I found one of the 18 726. That's very nearly 67 years. As a North American male born in the late 1970s, my life expectancy is probably little more than 70 years, so we can safely say that I will be quite dead before I find the proverbial girl of my dreams. Come to think of it, she'll probably be dead too.

So there you have it, my friends—finally, a cogent, scientific, non-self-deprecating argument for why I will never have a girlfriend. That said, if you happen to be a girl deluded enough to think that you and I have a chance together, feel free to drop me a line, but I warn you, you face odds of 157 060 to 1. I wouldn't bother if I were you.

Update (2000-04-01): My sarcastic pleas for some e-mail have finally been answered. Take a look at this letter from a hysterical female reader, which I think perfectly demonstrates the point of this entire essay. (I think the fact that she's a WebTV user explains a lot—in fact, I was sure this e-mail was an April Fool's joke until I noticed the return address.)

Endnotes and references

1. ↑ This paper was written when the author was at Griffith University, Australia.
2. ↑ After a short period of brooding, of course, these males will eventually come to the realization that the real reason they were never able to get a girlfriend is that they were too discriminating with their attentions. They will consequently return to the dating scene, entering a sequence of blasé relationships with mediocre girls for whom they don't really care, until they finally marry one out of fear of spending the rest of their lives alone. I am convinced that this behaviour is the real reason for today's alarmingly high divorce rate.
3. ↑ Due to rounding, figures cited may not add up exactly.
4. ↑ ^4.0 4.1 U.S. Bureau of the Census, Report WP/98, World Population Profile: 1998, Table A-3. Washington, DC: U.S. Government Printing Office, 1999.
5. ↑ ^{5.0 5.1 5.2} U.S. Bureau of the Census, Report WP/98, World Population Profile: 1998, Table A-7. Washington, DC: U.S. Government Printing Office, 1999.
6. ↑ WP/98 gives the annual death rate for developed countries as 10 per 1000, but does not list death rates per age group. Presumably, the death rate graphs as a bathtub curve, but in absence of any numbers supporting this hypothesis, and for the sake of simplicity, I will conservatively estimate the death rate among this age group to be 1% biennially.
7. ↑ Despite my efforts to research the matter, I could find no data on the distribution of beauty, either outer or inner, amongst the population. Perhaps attractiveness, being a largely subjective trait, does not lend itself to quantification. It is not unreasonable, however, to assume that like most other traits, it has a normal distribution. Indeed, this assumption seems to be backed up by informal observation and judgment—in any reasonably large group of people, most of them will be average-looking, and a tiny minority either exceedingly beautiful or exceedingly ugly.