It is springtime on the island. A crop of new baby birds hatches out as usual. The ever-changing environment into which they are born happens, by sheer chance, to experience an unusual drought in their very first year of life. The round little red seeds their species mostly lives on are in short supply that summer and fall. Many of their feather become malnourished, quite a few grow so weak that they die before they can reproduce.

Also by sheer chance, one of the baby birds bears a mutation within its DNA which, oddly enough, does not cause it to die, as usually happens. Instead, it gives the baby bird a slightly narrow, pointy beak. The other little birds, with their stout little wide beaks, think the new baby looks odd. Squeak Beak, they call him, derisively, uncaring that their jeers hurt the little fellow’s feelings. But justice works in odd ways. As they slowly starve for lack of round little red seeds, they observe Squeak Beak getting fatter and robust.

By sheer chance, a new invasive plant floated in and invaded the island last year, and it spread like—well, like unloved plants typically do everywhere. This new plant produces nutritious little green seeds in plenty, but they’re hard to get at. These seeds are encased in a hard little pod that, when mature, splits open along narrow little vertical cracks just barely wide enough to let the little green seeds fall out. They’re slow to fall out, so they are quite fully matured before finally doing so. And they’re very nutritious.

As it happens, Squeak Beak’s odd little mutated beak is just narrow enough to fit nicely into the cracks in the green seed pods. He has a field day—the new diet is delicious. He grows robust and healthy from daily plenty of the green seeds while his peers are dying off, because he has the only beak in town that can reach through the narrow cracks to get to the seeds. With little competition for the surviving girl birds, Squeak Beak has his way with all of them, and gloats. In due course some dozens of new baby birds hatch out on the island. Nearly all have cute little narrow beaks. They all adore the luscious little narrow green seeds which grow in such plenty everywhere on the island now, not to mention those fat round red seeds which come roaring back when the drought ends and the rains return. These narrow-beaked babes are the new normal. Come next season, their children will adore both red and green seeds too. They have been naturally selected, the fittest to survive (in the narrow view of things). Life on the island has evolved.

Meanwhile, also by chance, a shipwreck releases several old-world rats onto the island—the first rats ever to inhabit it. The rats learn quickly—not to worry—there’s plenty of food around here. Those red seeds aren’t bad, and there’s plenty of those tasty little green seeds which are a tad hard to get out of their hard shell but can be got out if you want to bother. Best of all, there’s all these delicious song birds with little narrow beaks…

If you’d like to read the full context of this portentous story I recommend Jonathan Weiner’s wonderful little book The Beak of the Finch (Vintage Books, 1995). Squeak Beak’s interesting adventure in natural selection also embodies a basic principle of life which may be described thus. Living creatures become naturally “selected” to survive long enough to reproduce (meaning they make it while others don’t) when the physical and mental characteristics with which they were born are better able to accommodate changes in their environment than are others of their kind which lack such particular adaptive characteristics. A very small nuance of difference in bodily characteristics, such as beak width, can give one individual a decisive advantage over others of its kind, and even a very slight advantage can make the difference as to whether one survives an environmental change and another does not.

There is of course a great deal more to biological evolution and speciation than the small accidents that attend DNA transmission, as must be understood by anyone who has read the sound symbiotic reasoning of Lynn Margulis, James Lovelock and many like minded colleagues. But for now it is enough that the point of the beak be understood. No creature has any say about its personal features that convey survival advantage or disadvantage, for these features are handed down, by sheer chance, from 1) the combined DNA of the creature’s parents, whoever they may be, and 2) whether the two parental DNAs chance to combine properly, or not. There’s also a third possibility:  With bad luck, lethal cosmic rays arriving from outer space, not to mention the X-ray machine down the hall, can accidentally change a few important details in a creature’s DNA—even creatures such as  you and me. It all means this:  When the environment within which a creature resides changes in some way, whether or not the creature is equipped to adapt to the change, and survive, is usually luck of the draw…