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common ancestor more easily than the differences between chimps and the common ancestor,” observes Zhang. The result makes sense, he says, because until recently the human population has been smaller than that of chimps, leaving us more vulnerable to random fluctuations in gene frequencies. This prevents natural selection from having as strong an effect overall. Now the macaque genome has been sequenced (see page 15), biologists will be able to learn more about the differences between the apes. have been transformed by natural selection show an unusually high proportion of these mutations. Zhang’s team found that 233 chimp genes, compared with only 154 human ones, have been changed by selection since chimps and humans split from their common ancestor about 6 million years ago (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.0701705104). This contradicts what most evolutionary biologists had assumed. “We tend to see the differences between us and our PEOPLE who use their cellphone while driving often claim it is no worse than chatting to someone sitting in the passenger seat. Suzanne McEvoy has news for them: it’s twice as bad. Two years ago, McEvoy and her colleagues at the George Institute for International Health in Sydney, Australia, revealed that drivers using a phone are four times as likely to have a crash that puts them in hospital as someone who is not, even if the phone is a hands- free model (New Scientist, 16 July 2005, p 4). The finding drew flak from those who said that talking to a passenger was probably just as distracting, so they have followed this up with a survey in which they asked 274 drivers admitted to a Perth hospital what may have distracted them in the five minutes before their accident. The results, to be published in Accident Analysis and Prevention, show that driving with one passenger makes an accident 38 per cent more likely, while travelling with two passengers increased the likelihood of an accident by a factor of 2.23. Those who were using a phone while driving with no passengers were 4.10 times as likely to crash. If you’re driving, stay off the phone “HOW did all this beautiful, crisp structure form?” asks Peter Tuthill. “That’s the million dollar question.” The structure in question belongs to a nebula just discovered by Tuthill, of the University of Sydney, Australia, and colleague James Lloyd of Cornell University in Ithaca, New York. They have called it the Red Square. The object displays a dazzling, gem-like symmetry (Science, vol 316, p 247). Most striking planetary nebulae are produced by low-mass stars like the sun, which shed their outer layers at the end of their lives. The star at the heart of the Red Square, called MWC 922, appears to be much bigger than the sun, suggesting that another process formed its signature shape. Tuthill says that a binary star system may be responsible. If one of the pair were losing matter, the gravity of both stars would pull the matter into a dense disc around them. Light and matter would only be able to escape the system from the poles of this disc, explaining why the nebula looks like two cones whose tips are touching. The yellowish-orange lines around the base of the cones may be the result of a particularly strong but brief outburst from the dying star. The team studied the Red Square using the Hale Telescope at Palomar Observatory in California and the Keck II telescope in Hawaii. AT 8 metres long, it had to be hauled out of the ground with a hydraulic lift normally reserved for dinosaurs. But this fossil formed around 385 million years ago – long before dinosaurs even existed. It’s a tree from the Gilboa fossil forest, New York. The site – which contains the oldest trees in the fossil record – is well known to palaeontologists, who until now had only uncovered fossil tree stumps, leaving them guessing about the appearance of the tree tops. Now they know: the trunk had large branches, with fronds similar to a modern-day tree fern – although they were unrelated to tree ferns. The fossil tree has been assigned to a group of plants known as cladoxylopsids (Nature, vol 446, p 904). A forest of such trees would have provided a rich habitat for other organisms, as well as boosting ancient Earth’s biodiversity, says team member Chris Berry of Cardiff University, UK. Indeed, fossils of millipede-like detritivores were found at the site. Such forests may also account for the drop in atmospheric carbon dioxide levels seen in the fossil record around that time. “The rise of forests must have had some impact on atmospheric carbon dioxide and therefore the Earth system,” says Berry. IT’S time to stop thinking we’re the pinnacle of evolutionary success, folks. The fact is, chimpanzees are the more highly evolved species. Evolutionary geneticist Jianzhi Zhang and his colleagues at the University of Michigan, Ann Arbor, compared DNA sequences for 13,888 human, chimp and rhesus macaque genes. For each DNA letter at which the human or chimp genes differ from the ancestral form – represented by the corresponding gene in macaques – they noted whether the change led to an altered protein. Genes that ALBERT GNIDICA/NEW YORK STATE MUSEUM P TUTHILL/PALOMAR OBS/KECK OBS Who is the most refined ape of them all? It’s big, heavy and looks like a fern Twin star clue to Red Square puzzle www.newscientist.com 21 April 2007 | NewScientist | 17
