More than 50% of your body heat is lost through your head. That's why in the wintertime we wear a toque (a woolen hat).
Staying alive
Staying alive The idea that ageing is simply a matter of cells
wearing out is being challenged by new research based on the work
of Max Rubner, a German physiologist who lived at the beginning of
the 1900s. He was the first to study the connection between how
quickly animals burn calories and how long they live. This line of
work has now been taken further by Steven Austad, a researcher at
the University of Idaho, who has discovered that the figures for
different species are remarkably similar. For instance, a gram of
guinea pig uses 260 calories in a lifetime compared with 280
calories per gram of horse. The theory explains that the faster the
cells utilise that energy, the sooner the animal dies. Most
scientists believe that this explains why smaller animals tend to
have shorter lives.
However, when animals are studied in their natural habitats, rather
than in the laboratory, a different picture emerges. For example,
birds have considerably higher metabolic rates than similar-sized
mammals but live more than twice as long. Looking at ecology and
evolution can help to explain why some species are fated to die
younger. According to Austad, smaller mammals grow old more quickly
not because they are living faster‚ metabolically speaking,
but because the their bodies are designed to live only a few years
as they will probably fall victim to larger predator within those
few years.
Researchers are now starting to look at the cellular defences and
repair mechanisms that keep animals youthful. Longer-lived species
tend to have higher levels of an antioxidant enzyme for any given
metabolic rate. And in the case of humans, language evolved so that
we could share our survival strategies with each other. Perhaps
this is why we enjoy a maximum life span four times that predicted
by our size and metabolic rate. 23 OCTOBER 1999, P. 31-35
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