Sunday, February 06, 2005

Who’s on First?
In December’s “The Hidden History of Men” by Robert Kunzig, anthropological geneticist Spencer Wells claims that “we can definitely rule out a date prior to 20,000 years ago” for the arrival of the first humans in the Americas. Yet archaeologist Albert Goodyear of the University of South Carolina has recently claimed to have found evidence that humans were in North America 50,000 years ago. Goodyear bases his conclusions on radiocarbon dating, whereas Wells uses genetic markers for his conclusions. What should we make of this?

Eric Peters
Ashland, Oregon

The initial settlement of the Americas is a contentious issue, with researchers falling into two camps. One, supported by copious archaeological and genetic evidence, favors a settlement from Siberia via the Bering Land Bridge within the past 20,000 years. The other camp posits a wave of migration as early as 40,000 years ago. The finds made at the South Carolina site have not yet been described in the scientific literature, so I have no way to evaluate them properly. It is likely, though, that the 50,000-year-old “tools” found there were produced by natural flaking, not human manufacture, and that the charred plant remains resulted from a natural fire. If the tools and charred remains do stand up to scrutiny, then there is an intriguing, although unlikely, possibility. Given the recent discovery in Flores of a dwarf hominid species related to Homo erectus, it is possible that H. erectus made it to more places than we have evidence for. H. erectus was primarily a tropical or subtropical species, and there is no evidence suggesting that it ever managed to live in the Arctic. Perhaps one day we will find the remains of a subpopulation that adapted to life in northern latitudes in the same way that Neanderthals did in Europe, leaving them poised to make the leap into the Americas. Crucially, though, even if H. erectus did make it through the Arctic and into the Americas, they don’t appear to have passed on their genes to us. They would be distant cousins, not great-great, etc. grandparents. The genetic evidence we have is clear: All non-Africans came out of Africa within the past 60,000 years, and the ancestors of today’s Native Americans entered the Americas within the past 20,000 years. If there were other hominids living here when modern humans arrived, they must have died out. While the study of extinct species can yield many fascinating details about the complexities of hominid evolution, it doesn’t tell us about our own species’ genealogy—only the clues in our genes can do this.
Spencer Wells

The High Cost of Expansion
Theoretical physicist Michio Kaku’s article “How to Survive the End of the Universe” [December] missed a potential solution: harnessing dark energy. If we accept the premise that dark energy exists, and that it causes the expansion of the universe to accelerate, this represents an enormous source of “free” energy. Assuming that the expansion continues to accelerate ad infinitum requires that this source of energy will also exist ad infinitum. It’s not energy that we can tap into, but the Type II and III civilizations discussed in the article could.

Geoff Hart
Pointe-Claire, Quebec

In “How to Survive the End of the Universe,” we read about the theory suggesting that as the universe expands and its rate of expansion increases, distant objects move away from us faster than the speed of light. How do we reconcile this with the special theory of relativity, which says that nothing can go faster than the speed of light?

Bill Callahan
Franklin, Massachusetts

The more precise statement is that no usable information can travel faster than light. For example, in general relativity, empty space can expand faster than light, which explains why in the Big Bang scenario the universe expanded faster than the speed of light. In fact, in the inflationary universe theory, the empty space of the universe expanded trillions of times faster than light. And billions of years from now, if the universe continues to accelerate, distant galaxies will recede from us faster than light and will no longer be visible. In the distant future, astronomers may mistakenly conclude that the entire universe consists of just a handful of galaxies in our local vicinity because all the distant galaxies are receding from us so fast that light cannot reach us. Scientists have performed the Einstein-Rosen-Podolsky experiment in the lab, showing that information can travel by light beams faster than light; however, the information being transmitted is random and hence useless.
Michio Kaku

What’s in a Name?
Regarding The Race to Save the Lord God Bird [Reviews, December]: I met Lord God woodpeckers in the early 1950s, when my family moved from southern to northern rural Louisiana. Then it was the pileated rather than the ivory-billed woodpecker that went by this strange name. I pondered for years how a woodpecker could get such a name, until I discovered Birds of America, edited by T. Gilbert Pearson, whose other names for the pileated woodpecker included “Logcock, Lord God, Good God, and Great God woodpecker.” I then realized that “Lord God” was probably a corruption of the word logcock, a name that apparently derived from this woodpecker’s habit of foraging on rotten logs.

Berlin A. Heck
Broken Bow, Oklahoma

The Case for Planet Y
Your November cover illustration for “Beyond Pluto” shows four planets: Pluto, Sedna, Planet X, and Planet Y. I know Planet Y is theoretical, but what makes us think it could be there?

Garrett Anderson
Colorado Springs, Colorado

The evidence of Planet Y is speculative. Based on various lines of indirect evidence, astronomers are fairly sure that the sun is surrounded by a huge cloud of dormant comets—trillions of them, probably—that move in lazy orbits extending halfway to the nearby stars. This so-called Oort cloud eventually blends into the equivalent cometary clouds surrounding our neighboring stars. Mathematical models, combined with our understanding of how planets and comets form, suggest that the objects in the Oort cloud must have been flung there by one of the giant planets closer to the sun. The vast majority of the objects out there are presumably the size of the comets we see, about 5 to 20 miles across. But planetary astronomer Mike Brown and others infer that larger, planet-size bodies could have also been exiled to the Oort cloud; this is the basis for our Planet Y.
The editors

*In the fourth item in December’s Flash (R&D), the second sentence should have read, “Participating countries must reduce CO2 output to 5 percent below 1990 levels by 2012.”


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