Geochemistry. Two geologic clocks finally keeping the same time.

old, but it seems to correspond to a grade of hominin that ceased to walk on the Earth a few million years ago, " says Wood. " How it got there and managed to persist—that's clearly a challenge to explain. " One explanation is that the hobbit stems from a very ancient migration of a primitive hominin out of Africa. H. habilis, for example, had a short stature and a smaller brain than later hominins did, so it's easier to derive something hobbitlike from such an ancestor, Jungers said. But there's no other evidence anywhere in the world of such an early exodus out of Africa. Such a hypothesis requires " special pleading, " says paleoanthropologist Russell Ciochon of the University of Iowa, Iowa City. Australop-ithecine expert William Kimbel of the Institute of Human Origins at Arizona State University in Tucson agrees. " I'm not ready to go back to the Early Pleistocene of Africa for an ancestor , " he says. " That spans a lot of time and space, and I'm not comfortable with those gaps. " Ciochon thinks the evidence suggests that a more recent ancestor, perhaps H. erectus itself, shrank to hobbit size in an evolutionary dwarfing process. For other researchers, the whole debate is moot because they view LB1 as simply an aberrant H. sapiens. The foot " is such a mixture of characters, requiring very convoluted evolutionary and biomechanical explanations, that a developmental anomaly in a pathological human seems much more parsimonious, " says paleopathologist Maciej Henneberg of the University of Adelaide in Australia, a longtime hobbit critic. A few recent papers have expressed such skepticism. The authors of a controversial report on small-bodied H. sapiens skeletons on the island of Palau argue that LB1 could have been a small-bodied H. sapiens, too (ScienceNOW, 11 March: sciencenow.sciencemag.org/cgi/content/ full/2008/311/1). And several papers have attributed LB1's peculiarities to micro-cephaly, Laron syndrome, and most recently, cretinism, in a procession Dean Falk of Florida State University in Tallahassee calls Brainteaser. Researchers continue to puzzle over why the hobbit's cranium is so tiny. First the bedroom clock reassures you that you're right on schedule. Moments later, the kitchen clock tells you that you're running minutes behind. If you find that annoying, pity the geochronologists. For decades, two of their workhorse timepieces—isotopic clocks ticking to the steady decay of two different radioactive elements—have been disagreeing by millions of years. Now …