Genes, Ageing and Evolution

Creatures that are better able to defend themselves through their size and strength like tigers, or their adaptability like humans, or by having the tough shell of a turtle, have genes that give them a normally longer life than that of smaller, weaker creatures. Their genes did not make this so. Genes in the creatures that lived longer were allowed to evolve to a capability of providing the longer life normal for those creatures.

Creatures that managed to live a little longer than others within a species and also had longer-life genes than others -- genes coded for slower ageing -- grew to represent a greater percentage of their species, and their longer-life genes became the dominant characteristic of their specie. Over a period of say a million years, creatures with good survivability could incrementally incease their genetically normal life-span.

Small birds who can defend themselves by flying away from danger live for a decade or more whereas mice, who cannot, die of old age in a year or two. Being very well defended, tortoises and turtles can live for over a hundred years.

Energy use is involved. A change in the environment that produced a shorter lifespan lent greater survivability to those members of a specie that were more genetically oriented toward putting energy into reproduction rather than bodily repair necessary for longer living. Their genes evolved toward a shorter life-span.

Energy involvement worked against the humingbird's speed and ability to defend itself through flight. A hummingbird's extremely fast wings consume vast amounts of Adenosine triphosphate (cellular energy molecules) and cause the hummingbird's heart to deteriorate with permanent and long-term wear. This results in hummingbirds usually dying shortly after reproducing.

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