Monday 27 January 1997
If you have a tense, nervous headache, don't blame mechanical tension. That's what helps to hold your neurons together and allowed your cerebral cortex to fold so thoroughly. That's the suggestion (at least, the bit about the tension is) from David Van Essen at Washington University, Missouri, who in last week's edition of Nature suggests that the mechanical tension along parallel fibres in the cortex can explain why the average cerebral cortex is so highly folded that it has a surface area of about 1,600 square centimetres - three time what it would be without any convolutions.
Why scream while you're being eaten by a tiger? Maybe it is the sort of question only scientists would ask, but it's particularly the kind that puzzles behavioural ecologists. Is it to warn other potential victims away? Or to attract help? A new experiment with pike and minnows (the former eats the latter) by a Canadian team found a third reason: you might attract another predator which would fight the first one for you, the trophy - giving you the chance to slip away. Worth bearing in mind if you're an explorer ...
The smell of garlic on somebody's breath doesn't come directly from the plant itself, but from chemical changes in the blood, according to a team from the University of Innsbruck in Austria. Three compounds - allyl methyl sulphide, dimethyl sulphide and acetone - took some hours to reach their peak level in blood, and were still present 30 hours later. But acetone is produced by degradation of fatty compounds in the blood, including cholesterol, and its concentration in subjects' breath was higher than that from crushed garlic.
Hawaii, California and Florida have the most endangered species, according to a new map of biodiversity in the US, drawn up by a team from Princeton University. The map shows "hot spots" where unusually large numbers of endangered species are found: unsurprisingly, these tend to overlap with intensive urbanisation and agriculture. Such species also tend to be "endemic" (restricted in their ability to shift to new sites) and so are prone to extinction. Knowing where the hot spots are can help save species, because a large proportion of endangered species can be protected on a small proportion of land, say the authors.
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