Bully for Brontosaurus (36 page)

As for recurrent, small-scale variation (individual differences, in Darwin’s terminology), blending posed no insurmountable problem, and Darwin had resolved the issue in his own mind long before reading Jenkin. A blending variation can still establish itself in a population under two conditions: first, if the favorable variation continues to arise anew so that any dilution by blending can be balanced by reappearances, thus keeping the trait visible to natural selection; second, if individuals bearing the favored trait can recognize each other and mate preferentially—a process known as assortative mating in evolutionary jargon. Assortative mating can arise for several reasons, including aesthetic preference for mates of one’s own appearance and simple isolation of the favored variants from normal individuals. Darwin recognized both recurrent appearance and isolation as the primary reasons for natural selection’s continued power in the face of blending.

With this background, we can finally exhume the real point and logic of Jenkin’s essay—an issue still very much alive, and discussed (through all his factual errors) in a most interesting and perceptive way by Fleeming Jenkin. Jenkin’s essay is a critique of Darwin’s continuationist perspective—his distinctive claim, still maintained by the evolutionary orthodoxy—that all large-scale phenomena of evolution may be rendered by accumulating, through vast amounts of time, the tiny changes that we observe in modern populations. I call this conventional view the “extrapolationist” argument; I also share Jenkin’s opinion (but for different reasons) that this traditional mode of thinking cannot explain all of evolution. I find it supremely ironic that the one small section of Jenkin’s article
not
about Darwin’s claim for continuity (his argument that single sports will be swamped by blending) has become the only part that we remember—and, to make matters worse, usually misinterpret. Such, however, is the usual fate of Whig heroes and villains.

A simple, almost pedantic, précis of Jenkin’s argument should rescue his larger point. Jenkin’s essay proceeds in four parts. The first, on limits of variation, admits that Darwin’s favored style of recurrent, continuous variation does occur and can be manipulated by natural selection to change the average form of a species. But, Jenkin argues, such variations always fiddle in minor ways with parts already present; they cannot construct anything new. Thus, natural selection can make dogs big, small, blocky, or elongate—but cannot change a dog into something else. Jenkin expresses this argument in his powerful metaphor of the “sphere of variation.” Natural selection may move the average form anywhere within the sphere, but not beyond its fixed limits:

Common experience, Jenkin affirms, supports his view. Artificial selection practiced by breeders proceeds rapidly at first but soon reaches frustrating limits. Jenkin writes of racehorses:

Darwin, Jenkin claims, maintains an unwarranted faith in the power of simple time to overcome these barriers:

Darwin might argue, Jenkin admits, that once a species reaches the limit of its glass sphere, time will eventually reconstitute this edge as a new center and produce a new sphere around the previously peripheral point. Jenkin also rejects this argument:

Jenkin’s second section, on types of variation, begins by admitting Darwin’s point that small-scale recurrent variations will not be destroyed by blending. But these are the very variations subject to strict limits by the previous argument about rigid spheres. What kind of variation might then induce the evolution of something substantially new? Single sports might seem promising, but these are the rare events that will be swamped by blending—and readers may now note the point that Jenkin himself wished to make with the only part of his argument that we remember. But perhaps some kinds of sports do not blend and do perpetuate their kind. Fine, Jenkin admits. Perhaps such creatures do occasionally arise and produce new species. But such a process is not Darwinian evolution, for Darwin insisted that natural selection acts as a creative force by gradually accumulating favorable variants. Indeed, would such a process be very different from what the vernacular calls “creation”?

The third part argues that even if Darwin could find (which he can’t) some way to accumulate small-scale recurrent variations into something new, geology does not supply enough time for such a slow process. Here Jenkin relied on the false arguments of his dearest friend, Lord Kelvin, about the earth’s relatively young age (see Essay 8, on Kelvin, in
The Flamingo
’s
Smile
).

The last section presents a powerful (and I think entirely correct) argument about the difficulty of inferring historical pathways from current situations. Jenkin contends that nearly any current situation can arise via several historical routes; thus the situation by itself cannot specify the pathway. Jenkin points out that Darwin bases much of his argument upon the lack of definite boundaries in nature—the intergradation of species into species, or geographic region into region. Darwin’s continuationism predicts just such an absence of boundaries since species are gradually and imperceptibly changed into their descendants, while a creator should leave gaps between his incarnated objects. But Jenkin argues that many natural items come as continua, yet clearly do not arise by a process of historical transformation. Arguing, as he does throughout, by metaphor and analogy, Jenkin writes:

Taken as an entirety, Jenkin’s argument possesses a kind of relentless logic. The critique of Darwin’s extrapolationism serves as its unifying theme. Part one argues that small-scale variation cannot extend beyond fixed limits. Part two claims that no style of variation can make something substantially new in a Darwinian world. Part three proposes that even if Darwin could find a way, geology does not permit enough time. Finally, part four holds that we cannot infer historical transformations from the admitted continua of nature.

I don’t want to fall into a Whiggish pit and judge Jenkin by current standards (everything that has gone before in this essay adequately discharges, I hope, my dues to anti-Whiggery). But old arguments usually repay our close attention because we often stop discussing the fundamentals once an orthodoxy triumphs, and we need to consult the original debates in order to rediscover the largest issues—perhaps never really resolved but merely swept under a rug of concord. Much of Jenkin’s argument fails today, for few things last a century in science. He was clearly wrong about blending in part two and about time in part three. But I believe that he was right about continua in part four and that we are still plagued by a tendency to make an almost automatic inference about history when we fail to find clear boundaries.

The first argument about limits of variation has also risen again in current debates about evolutionary processes. I don’t accept Jenkin’s metaphor of the sphere, because small quantitative changes can accumulate to qualitative effects or leaps (contrary to Jenkin’s position), and because I accept Darwin’s argument that new spheres can be reconstituted about previously peripheral points.

But neither (probably) is a species the kind of almost equipotential sphere that strict Darwinians envisaged—unconstrained and capable of rolling anywhere that natural selection pushes. Constraints imposed by genetics and development have emerged as a central topic in contemporary evolutionary debate—and Fleeming Jenkin did present an insight worth considering.

In short, Darwin’s strictly extrapolationist vision may not describe large-scale evolution very well—small, local adaptations built in the refiner’s fire of Darwinian competition among organisms struggling for reproductive success may not, by extension, explain trends that persist for millions of years or relays of changing diversity that mass extinctions produce. Jenkin, who presented the most logical dissection of Darwin’s continuationist vision in 1867, does reach across a century to set us thinking, however superannuated his specific claims.

We may give the last word to Jenkin, via Robert Louis Stevenson. One day as a young man, Stevenson reports, Fleeming Jenkin argued bitterly with two young women about a pressing issue of Victorian hypermorality: Can a misdeed against moral codes ever be condoned, whatever the circumstances—stealing a knife to prevent a murder, for example? (Jenkin, to his credit, argued the affirmative.) As he left the house, his anger mellowed. He realized that even the most apparently peculiar belief deserves respect if argued honorably and if properly constructed upon a set of basic premises different from those usually cherished:

Postscript

My parochialism and ignorance in the case of Fleeming Jenkin were even deeper than I had realized. Having corrected the most blatant omission of failing to recognize the importance of his mainline career in engineering, I discovered, after publishing this essay, that I had also missed a tangential foray equal in importance to Jenkin’s critique of Darwin. Several professors of economics wrote to inform me that Jenkin had made cogent contributions to the “dismal science” as well.

Robert B. Ekelund, Jr., of Auburn University, stated:

Christopher Bell of Davidson College then sent me an article from
Oxford Economics Papers
(Volume 15, 1963) by A. D. Brownlie and M. F. Lloyd Prichard entitled “Professor Fleeming Jenkin, 1833–1885, Pioneer in Engineering and Political Economy.” This fascinating article cites the opinion of the great economist J. A. Schumpeter (1883–1950), who regarded Jenkin as “an economist of major importance, whose main papers…form an obvious stepping stone between J. S. Mill and Marshall.”

In a time of great industrial strife, and considerable opposition to trade unionism, Jenkin used his quantitative analysis of supply and demand to defend, as practical and necessary, the rights of workers to form associations for collective bargaining. He wrote that “the total abolition of trade unions is out of the question as impolitic, undeserved, and impossible…[But] we must insist that the great power granted to the bodies of workmen shall be administered under stringent regulations.”

Jenkin, scarcely a radical in politics, favored no massive redistribution of wealth, but only some minor tinkering for greater satisfaction and productivity of workers. He wrote: “Great inequality is necessary and desirable (observations seem to show that trade will extend faster with large profits and small wages than with small profits and large wages).” For, basically, Jenkin held firm to the ideals of the laissez-faire system so strongly identified with the intellectual history of his nation, particularly with Adam Smith in his own home city of Edinburgh. Jenkin wrote:

Yet Jenkin tempered the harshness of pure laissez-faire with a realization that the central argument, practically applied by people in power, almost always acted as a rationale for unfairness toward workers. He wrote:

A wonderful irony pervades all these themes, one that only an evolutionary biologist could fully identify and appreciate. Brownlie and Lloyd Prichard point out that Jenkin’s economic writings were consigned to oblivion, largely because the two great opinion makers of later nineteenth-century English economics, Jevons and Marshall, “treated him shabbily to say the least.” (Both Jevons and Marshall sensed that the “amateur” Jenkin had anticipated some of the “original” work that served as a basis of their own reputations. They therefore sought to disparage and discredit, and then to ignore, this gifted thinker, who did only limited work in economics and did not really threaten their turf, or even their prestige, in any large sense—an act, all too characteristic, alas, of conventional academic ungenerosity.)