Who has not dreamed of living forever? We know we won’t. Someone born
in Japan today has a life expectancy of about 83 years. A white American born
in 2010 is projected to live about 79 years on average, a black American 75
years. A French woman, Jeanne Calment, is said to have been mentally fully
competent when she died in 1997 at the age of 122 years.
But some other species live much longer. Greenland sharks (Somniosus
microcephalus) were recently found to live for at least 272 years, and the largest
individuals are estimated to be almost 400 years old [41]. This is impressive, but
hardly compares with a 5065-year-old bristlecone pine in California that is the
oldest known unitary (“individual”) organism. The quaking aspens that grow on
a mountain slope in the western United States appear to be separate trees but
are often a clone: a single genetic individual, originating from a single seed, that
may be more than 80,000 years old. Some organisms might well be immor-
tal: they show no signs of senescence, the intrinsic changes that lower survival
and reproduction with age. Some biologists think that clonal plants and fungal
mycelia do not senesce, and this may be true of some sponges (estimated at
more than 11,000 years old) and corals (more than 4000 years old). In contrast,
many plants, insects, and even some mammals live for only 1 year, many small
insects for only a few months, and some rotifers for fewer than 20 days (FIGURE
11.1). There exists enormous variation among organisms not only in maximum life
span, but also in the process of senescence that foreshadows ultimate demise
[29, 35, 45, 55].11
Parental care in many fishes is a male role, as in this male yellow-headed jawfish
(Opistognathus aurifrons). Having fertilized his mate’s eggs, he protects them
until they hatch by holding them in his mouth. This reproductive strategy limits
the number of offspring, but enhances their chance of survival.How to Be Fit
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