Evolution gets real
It’s Thanksgiving, so let’s not get into the evolution fight.
Whether divine providence or adaptive radiation did it, the variety
of life on planet Earth is astounding.
Evolution gets real
It’s Thanksgiving, so let’s not get into the evolution fight. Whether divine providence or adaptive radiation did it, the variety of life on planet Earth is astounding.
I’m most comfortable with a middle-of-the-road approach. I believe evolution continues to take place because a divine being allows it to be so.
The parts fit so elegantly into a whole, and the more we understand, the less we seem to know. As humans, we’re comparatively weak, slow and helpless. But we’re blessed with enormous brains that allow us to cloak ourselves in devices that compensate for our helplessness.
Other animals have developed other strategies.
Our gardens and woods are full of a winter visitor that’s pretty non-descript. Yellow-rumped Warblers are mostly gray with a few patches of bright yellow. Small, they measure no more than 5.5 inches long. The first clue that one or more are in the neighborhood is usually a sharp “pik!” call note. Those in our garden feast on ripening olives that we find to be inedibly bitter. But their rich oil content supplies precious calories to the wintering butter-butts – the nickname many birders are fond of using.
The birds breed in Canada and the interior U.S., but they’re abundant locally through winter.
Unlike most warblers, the Yellow-rump does not subject itself to the ordeal of a long migration.
Warblers subsist primarily on insects, and when the weather turns chilly and the food supply grows short, they must travel to the tropics to secure calories adequate to survive.
The Yellow-rump has developed a different strategy. Each fall, the bird grows a longer intestine, one designed to extract nutrition from seeds and other harder-to-digest food items.
In spring, as the days lengthen, the bird’s anatomy changes and the bird reverts to an insect-based diet.
The price of flight is high. To be light enough to beat gravity at its own game, birds are built-around feather-weight skeletons. Females have only one ovary, and except when laying eggs, it is atrophied to an insignificant size.
Calories are the currency of wildlife. Birds migrate for food, habitat and breeding opportunities. But the job of migration is both perilous and arduous. The cost in terms of calories is enormous.
By evolving to a degree in which the bird’s body physically adapts, the Yellow-rump saves itself the trouble of an annual trip to Central America, as most warblers do.
If that does not fill you with awe, you must be spiritually impoverished.
As I write this, a friend called to gasp that as he was watching a Sharp-shinned Hawk along Llagas Creek east of Gilroy, a Red-shouldered Hawk swooped in and tried to kill its smaller rival – a Wild Kingdom moment if there ever was one.
Nature is at our doorstep. Enjoy the holiday, and for Pete’s sake, do something outside.
