On the Nature of Natural Selection

Amanda M. Sparkman


Assistant Professor of Biology

Westmont College

January 2016

When you hear the words “natural selection,” your first associations may be Herbert Spencer’s “survival of the fittest,” Tennyson’s “nature red in tooth and claw,” or even Darwin’s own “struggle for life.” Over the past 150 years, these associations have clustered around the theory of evolution by natural selection, sometimes casting it in a shadowy light, with uncomfortable moral resonances. Natural selection certainly does reside in the shadows, deftly shaping organisms that are better able to track, hunt, kill, and devour one another—or to steal their neighbor’s food, mate or home, while carefully guarding their own. Selection may favor the tooth and the claw, the lure and the sucker, the sharpest of eyes and ears and noses—and the strong over the weak. Yet if we fill our imaginations with these images alone, we may end up missing something fundamental about what selection actually is and does.

Contrary to popular perception, natural selection is not first and foremost about killing, selfishness, or even necessarily survival. Natural selection is about bearing young: about who bears young, and how many. It is about generation, procreation. To bear young, you must survive to maturity. You must find at least one mate. And you must give birth to young that will develop and persist to maturity, mate, and bear their own young. You must do this in a finite world where water, warmth, light, space, food or mates may be in limited supply; where others may share your needs, or want to consume you to satisfy their own. Natural selection is simply the process by which forms or behaviors that allow individuals to successfully bear young spread through a population, passed down genetically from generation to generation, even as forms and behaviors that limit ability to bear young decline in frequency over time.

The forms and behaviors that spread and proliferate through natural selection constitute the diversity of life on earth. Sharp canines that tear flesh. Hefty molars that grind grasses. Taproots that draw on water deep in the ground. Broad leaves that gather light under a canopy. Courting males that proffer dead insects or fish to hungry females. Older young that stay to help their parents raise younger siblings, and parents that help protect their young from predators. Males with barbed genitals that force themselves on females, and females that ward them off with genital shields. Plants that offer fruit to birds, and birds that disperse their seeds. Parasites that travel from host to host, feasting in limbs and guts, brains and gonads.

Natural selection shapes this diversity in both the presence and absence of conflict. Consider a population of two large, extended families or lineages. If individuals in one lineage better monopolize food resources than the other, that lineage will proliferate over time while causing the other to dwindle. In stark terms, the aggressors will thrive as the meek starve. But the story need not be so stark. Consider one lineage with a higher tolerance for salt water that raises five offspring per family per year, and another more salt-intolerant that raises only one offspring per family per year. The salt-tolerant lineage would increase in numbers over time, while the increasingly small salt-intolerant lineage could wink out simply due to chance. Quietly. No aggression, no strife. Not even any additional suffering, necessarily, for individuals in salt-intolerant lineages.

Biologists themselves have been largely preoccupied with “nature red in tooth and claw” and have generated a vast body of theoretical and empirical literature on predation and competition (though research on mutualistic and cooperative relationships has shown a steep rise in recent decades). Even so, the study of antagonistic interactions itself reveals glimmerings of a gentler side to natural selection. For every armament involved in predation or parasitism—whether it be web, horn, spine, or venom—counter-evolutionary defenses have developed, such as visual or chemical camouflage, armor, speed, and immune response. Furthermore, even within the most fiercely competitive species, altercations involving severe injury or death occur relatively rarely. Instead, many species engage in ritualized displays, sometimes roughing each other up, but other times singing or dancing at each other, patting heads, urinating, or waving large appendages. Natural selection acts powerfully against extreme forms of violence, which can be costly for both parties. Thus even at this basic level, selection can act to protect and preserve individual lives.

Whether dealing in conflict or cooperation, natural selection favors a proliferation of strategies for efficient, effective living in a particular ecological context. If there is any metaphysical meaning to be gleaned here, it lies not only in the reality that selection involves conflict and suffering, and that some lineages decline, but also in the miracle that any lineages persist in a world rife with scarcity and accident. And that these lineages are so intricately, astonishingly, and even beautifully adapted to meet the diverse challenges they face.

I do not contend that natural selection can sometimes be “good,” sometimes “bad,” and that we should strive to see both these sides to have a fair and balanced view. Natural selection bears no clear relationship to morality, even when it selects for certain behaviors that resonate with actions and experiences that humans themselves find immoral or moral—or involve great suffering. Yet I also recognize that at some deep level, it may be appropriate, and perhaps even necessary, for humans to use morally loaded metaphors of selfishness, conflict, and struggle to describe natural selection as we try to come to grips with how the world works and our place within it. But if so, it also seems appropriate that, as we comprehend more clearly the nature of natural selection, we would engage it with metaphors of peacemaking, ingenuity, perseverance, and perhaps even hope.

AMANDA SPARKMAN is assistant professor of biology at Westmont College.


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