Whose Adaptation?


The word “adaptation” is much used when discussing evolution, all too often weighed down by an explicit or implicit “survival of the fittest” baggage.  Yet what the word “adaptation” actually means or what constitutes “fitness” is seldom clear.  Regardless of the context, speakers or writers usually look at these concepts from a human viewpoint, that is what we as humans would logically expect an adaptation to look like or do, or what our standards of fitness would be.  It is this human viewpoint that formed the conceptual foundation of Social Darwinism, a theory which unfortunately survives in many people’s thinking, including that of certain politicians and corporate CEOs, even as the term itself has fallen into disrepute.

But evolution does not operate according to what human beings, only one of its many products, think.  “Fitness” has nothing to do with how beautiful, successful, intelligent, or strong an individual happens to be; it has nothing much to do with individuals per se at all.  Fitness is determined by survival, but not by the survival, and certainly not the longevity, of a particular individual; rather, fitness is determined by reproductive fitness, that is, how successful are genetically related individuals (considered as members of their biological group) in producing progeny which in their turn also are reproductively successful.  If an individual reproduces, he or she is fit; if an individual does not reproduce, he or she is not fit.  How reproductive fitness works varies among species: some insects, for example, die immediately after laying their eggs—they live very short lives and never see their own offspring; mammals generally live long enough to raise their young to at least weaning age, and most larger mammals live long enough to reproduce several times and even to care for the offspring of their offspring (grandchildren).  But this multigenerational longevity is not evolutionarily necessary and not all living things have it.

In many advanced industrial societies today, a significant percentage of adults of reproductive age choose not to have children, preferring instead to concentrate on their careers or to enjoy the fruits of their labor rather than share them with offspring.  There are other reasons given for not having children as well.  Regardless of the reasons, not having children, failing to reproduce, means that such individuals are evolutionary dead ends—by Darwinian definition, they are not fit.  They may be too proud to think so, but a successful career will be quickly forgotten, if it was ever noticed in the first place, but DNA passed on is forever.  Thus the relatively poor person who has many children and grandchildren, etc., is evolutionarily fit, while the relatively rich person who has no descendents is evolutionarily unfit.  Because we are cultural creatures, we do not usually think this way; we laud the contributions to society of the childless genius and worry not a whit that he or she had no children—their contributions, in our minds, outweigh considerations of evolutionary fitness.  This is fine—it’s part of what makes us human, but we should not confuse cultural concepts of success with purely biological fitness.

Similarly, adaptation should not be viewed in human terms; adaptation is not limited to the beautiful, the visibly healthy, the perfect.  An adaptation is simply a characteristic or trait that either enhances reproductive survival or at least does not diminish it.  Blue eye color in humans is not an adaptation because it has little to no effect on reproductive success, either positive or negative.  Some people like blue eyes, some people don’t, and some people are indifferent to the color of their lover’s eyes.  Thus not every trait is an adaptation, strictly speaking.  Even some inherited diseases are neither adaptive nor maladaptive.  If a certain genetic line tends to develop a serious or fatal disease relatively late in life (i.e., after normal reproductive age), say Alzheimer’s or some form of cancer, evolution is indifferent to it, as it does not interfere with reproduction.

Some traits may be adaptive in one environment but maladaptive in another.  Fair skin among northern Europeans and other peoples of the north may be adaptive because it enables more efficient use of diminished sunlight to produce vitamin D, but fair skin in more equatorial climates is maladaptive; skin cancer rates are highest in those regions of the world where white people have migrated to sun-drenched climes, such as Australia or the American southwest.

Human beings, including scientists, are often unable to identify what is or is not an adaptation.  Take the example of the pinyon pine, a species of pine (Pinus edulis) common in northern Arizona.  According to researchers at Northern Arizona University in Flagstaff, pinyon pines vary in their resistance to the shoot-boring moth.  Looking at stands of pinyon pine, one would naturally tend to identify the moth-resistant individuals as more vigorous and fit than the moth-susceptible ones.  And under “normal” climatic conditions one would be correct.  But under drought conditions, the moth-susceptible trees are more fit—for some reason not yet clear, but likely having to do with the different fungal populations on their root systems.  So what looks like a maladaptation in one context looks like an adaptation in another.

If evolution worked according to the logic of the human mind, it would be a rickety failure.  Fortunately, evolution works at its own pace, quite indifferent to human theories, quite without plan or telos.  It has been doing so since long before humans were even a hint on the primate evolutionary tree, and will likely continue to do so long after our present species, Homo sapiens, has gone as extinct as the dinosaurs.

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