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Evolution uses seemingly useless

Jack Sprat could eat no fat,

His wife could eat no lean.

And so it was,



between the two,

They licked the platter clean.




When two species both eat the same food, they find themselves in competition. Since only so much food is available, a species can obtain more if it branches out, experimenting to find new ways to get its food or new foods to eat.

Some millions of years ago, the night was alive with moths (as it still is). They flitted from flower to flower, drinking nectar and, incidentally, transporting pollen. The moths’ populations were limited, however, to the number that could be supported by night-blooming flowers … until one line of moths evolved a new behavior, and began flying, gathering nectar and pollen, while the sun was shining. The world then saw its first butterflies.

Similarly, the vast majority of raptors (birds of prey) are daylight hunters; they miss out on the mice and rats that are active by night. But a change in behavior – along with the evolution of super-sensitive eyes, quiet wings and phenomenal hearing – allowed some birds to hunt at night, evolving into owls.

The utilization of different “niches” – different ways of making a living – allows millions of species to survive without undue competition. But should a niche disappear, the plants or animals that depend upon it will disappear, too. So will a host of other species that depend, for food or other resources, on the disappeared species.

Four billion years of evolution has emplaced on our planet a complex web of life, new species appearing as new opportunities appear, and themselves creating new opportunities for yet other species to show up.

Nature does not do things for a purpose; she does not, for instance, cause a rock to crack so that a tree can grow in the minuscule bit of soil that collects there. Rather, a tree seed happens to land in a crack in the rock, finds enough soil there in which to grow, and does so.

Of what use is a snag – a dead tree? Leafless, it can no longer make food through photosynthesis. As its roots rot away, they become ever less effective at holding the soil against erosion. The snag doesn’t even provide much shade.

Sporting a blue more brilliant than that of a Steller’s jay, the Western bluebird has, sadly, been disappearing from the foothills in recent years. It’s not that the jewel-like bird can’t find food, water or most of the other things it needs to complete its life cycle. But it is missing one thing – a place to nest. The Western bluebird is a cavity-nester, taking up lodging in holes that had been previously carved out of the softened wood of dead and dying trees by woodpeckers and decay.

By helping foothill residents to build nesting boxes, Sierra Foothills Audubon Society has been bringing the bluebird back to the region. Anyone putting up a few such boxes, however, soon realizes that bluebirds are not the only critters that need cavities to nest – others often take up lodging within.

Snags have been part of the landscape for millions of years – time enough for myriad organisms to have found myriad uses for them. Evolution, and the stresses that competition put on life, have made snags as essential as any other part of the ecosystem. Dismantling part of an ecosystem is tantamount to dismantling part of Creation – a decision that should not be made lightly.

Alan Stahler trained as a biologist and is an amateur astronomer. He teaches enrichment classes for children and adults at Sierra Friends Center. His science programs can be heard at noon on alternate Tuesdays on KVMR-FM (89.5).


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