The biology of senescence ensures that there are mortality hazards lurking in the older regions of the lifespan our society is now exploring. American Scientist is an illustrated bimonthly magazine of science and technology published by Sigma Xi, The Scientific Research Society. A less well-known type of sinkhole, however, develops in evaporite rocks such as gypsum and salt, which underlie 30 percent to 45 percent of the continental United States. One of the very earliest of these created two enzymes, each with distinct but related functions, where only one previously existed. Florida scrub-jays work together to raise offspring.
Some birds breed, and others simply help raise the young.
Scrub-jay helpers, says Schoech, can be breeders if they are given the chance. They are physiologically capable of breeding. He found that levels of the hormone prolactin correlate with the quantity of helping behavior that a bird performs. The computer has re-invigorated the field by enabling mathematicians to use approximate methods, zeroing in on the zeros with high speed and precision. Also in the January-February American Scientist , Henry Petroski takes a closer look at the steamship Great Eastern , a leviathan that, when launched in 1857, was twice as long and displaced 10 times as much as its nearest rival.