Mysteries of the Organism

Ian Tattersall is the author, most recently, of "Becoming Human" and "Extinct Humans" (with Jeffrey Schwartz). He is a curator at the American Museum of Natural History in New York City

Why are people so appalling? Why are people so admirable? Why are people as a whole--or even as individuals--so difficult to pin down? Why, indeed, are people so relentlessly driven to ask "Why?" Questions such as these, particularly in combination, cut close to the heart of what it means to be human, and "Human Natures" is an earnest attempt by the distinguished Stanford biologist Paul R. Ehrlich to provide an answer to the timeless conundrum that our strange species poses.

Ehrlich is broadly read and well-informed. His discussion ranges easily from the role of disease in human history to differences in perception of the world among different cultures and beyond, and what his book amounts to is the ruminations of an intelligent, sensitive and thoughtful biologist on a host of problems and considerations pertinent--in a variety of ways--to humanity's relationship, past and present, with the rest of the living world. It is a protracted, quirky and, in places, brilliant consideration of a remarkable range of topics that every concerned individual should be aware of. And despite a sometimes rather forbidding academic apparatus, it makes an enjoyable and frequently engrossing read.

Ehrlich discusses, for instance, why human females have concealed ovulation, how agriculture evolved and what the Easter Islanders did to transform it from a forested paradise to a wasteland capable of supporting only a small and deprived population that was a shadow of its former self. He considers humanity's place in nature: What we are doing to the world around us, whether it is possible for us to derive any ethical principles from the contemplation of the world beyond ourselves and, most important, what the prospects are for creating a "conscious evolutionary process" that will change our emphasis from simply "doing" to asking why.

At the beginning of "Human Natures" Ehrlich writes that this volume is in response to those reductionists who believe that all of our bizarre behaviors can be reduced to the influence of genes acquired many millenniums ago in our ancestral hunting-gathering "environment of evolutionary adaptedness." The first dozen pages or so contain the most concise and sensible summary I've seen anywhere of how genes, the factors of heredity, make individuals both alike and different. Indeed, in certain ways they make the remaining 400-odd remorselessly footnoted pages seem almost superfluous. (By the way, don't refer to the 2,000-odd endnotes as you read the book, for you'd quickly lose track of the bigger picture. But don't forget to browse through them--rather as you might an encyclopedia. Like the rest of the volume, these notes are a feast of odd observations, and are a large part of the fun of the whole thing.)

By the end of the book, however, it becomes hard to detect exactly where Ehrlich's sympathies lie on the matter of "evolutionary psychology," perhaps because his view of the evolutionary process itself is in some ways identical to that of the evolutionary psychologists. But his ambitions extend much further than the question of genes versus environment in determining how individual organisms turn out. Notably, in the case of our own species, he wants to broaden notions of biological evolution to embrace "cultural evolution." His belief is that a better understanding of evolution, and in particular natural selection, will help us deal with the host of rapidly intensifying problems that face humankind. Readers of Ehrlich's other works will not be surprised to learn that the problems that particularly worry him lie in the arena of our relationship with the environment that continues, if with increasing reluctance, to support us.

Close to a century and a half ago, Charles Darwin proposed that species of organisms should be expected to show slow change over time. Noting that individuals invariably differ in inherited ways and that in every generation far more offspring are typically born than will survive to reproduce themselves, Darwin argued that those most favored by nature--those "best adapted"--will leave a disproportionately large number of offspring. With the passage of generations, the advantageous adaptations of the favored individuals should thus become more common in their populations at the expense of less advantageous characteristics. "Natural selection" is simply Darwin's term for any and all factors that affect this process of differential reproduction and that cause slow change over the generations.

Darwin's notion had a bit of a rough ride at first, but by the middle of the last century it had become the accepted explanation for the time-related change that we see so widely documented in the fossil record. However, while there is certainly a role for natural selection in evolutionary theory, increasing numbers of biologists are coming to see that the evolutionary process is substantially more complex than this gradual linear grind would imply. Environments, for example, typically change rapidly, at rates that cannot be tracked by natural selection as traditionally conceived. What's more, the fossil record shows us that some species tend to come and go rather abruptly, and often remain unchanged over sometimes very long histories.

Clearly, there is more to evolution than fine-tuning by natural selection alone, and, as it turns out, a whole host of factors is involved. Perhaps the most important of these are speciation, the process (or processes) whereby new species come into being, and the fact that all "adaptations" are bundled up into individual organisms that have complex genetic structures. These fail or succeed as the sums of their parts rather than as possessors of specific favorable adaptations.

Nonetheless, an influential school of thought persists among biologists that looks to natural selection as the ultimate explanation of all evolutionary phenomena. Though Ehrlich remains acutely aware of the complexities of the biological world, at heart he belongs to this school.

The autobiographical aspects of this very personal book (he treasures his memories of field work among the Inuit of the Canadian Arctic) make it evident why. When he was in graduate school, Ehrlich examined the effects of the pesticide DDT on populations of fruit flies. While the results of these experiments taught him to be cautious of unwanted or unexpected outcomes, the power of (in this case, unnatural) selection impressed him greatly. Each generation of fruit flies is so short-lived that, by stringent selection, it is possible to produce large changes in remarkably brief periods of time.

As a result of this experience with the fruit flies, Ehrlich evidently became what is known as a "strict selectionist," an outlook that stays with him decades later. He is much too good a biologist to lack an appreciation of the complexity of the real world, but he apparently does not see much reason for looking beyond natural selection as an explanation for evolutionary histories of all kinds. This puts him in an awkward situation when he considers human evolution; for quite evidently there is much more to our evolutionary past than a simple singleminded trudge from primitiveness to perfection under the benevolent eye of natural selection.

Equally, because he is so wedded to the idea of natural selection as the sole significant mechanism of evolution, Ehrlich has a problem in distancing himself from the evolutionary psychologists, whose just-so stories about the fine-tuning of humans by natural selection imply a somewhat similar outlook. This is presumably why, having raised the issue of genes and behavior at the beginning of his book, Ehrlich largely lets it drop as his narrative progresses.

Almost certainly, though, the aspect of "Human Natures" that will attract the most controversy is Ehrlich's equation of biological evolution with what he calls "cultural evolution." Few would wish to deny that biological change occurs over time or that change takes place within human societies, but the roots of such change are, however, distinctly different.

For a start, biological change can only accumulate gradually, over generations, regardless of the histories of individual organisms, while cultural innovations can spread rapidly from individual to individual. The mechanisms of change thus are entirely different in culture and biology, and so are the expected results. All this Ehrlich knows perfectly well, of course, but he proceeds as though it doesn't make much difference. Indeed, he goes so far as to draw a close parallel between biological and cultural "macroevolution" (the evolution of larger groups in the one case, and the intervention of external influences in the other) and biological and cultural "microevolution" (biological and cultural changes within populations). This is perhaps a pity, since making this equation doesn't shed much light on the phenomena Ehrlich is interested in explaining, and many readers will be needlessly put off by this broadening of the notion of evolution, well beyond any practical utility. To simplify matters, I would recommend that readers substitute the word "history" whenever they encounter the term "cultural evolution."

But maybe all this doesn't matter very much, especially if one considers this book in isolation from Ehrlich's own claims for it. Indeed, so wide-ranging is his discussion that it is hopeless to try to summarize it in a short review. If there is a single bottom line, however, it is reflected in Ehrlich's title: Human nature, whatever it may be, is no simple matter. Humanity has, indeed, many natures, and it is in this almost self-evident observation that most of humankind's problems lie. "Human Natures" solves none of those problems, but it raises many, and places them in a thought-provoking perspective.

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