So much for prophesy. What the great German philosopher confidently declared to be “absurd” transpired less than a hundred years later. Darwin was precisely the “Newton of a blade of grass” that Kant predicted would never appear. The Origin of Species was the beginning of something big; but, as we have seen, it was far from the last word. In The End of Science: Facing the Limits of Knowledge in the Twilight of the Scientific Age (1996), the science writer John Horgan argues that evolutionary biology has effectively come to an end, not because it has failed miserably, but rather because it has succeeded so brilliantly. It has already solved all the major problems, and there's nothing left to do but simply tie up a few loose ends. Unlikely. A theme running through this book is that although Darwinism has indeed succeeded brilliantly in unraveling some of the deepest mysteries of nature, many issues concerning natural selection, adaptation, and directionality remain to be sorted out. Evolutionary biology is as vigorous as ever. The next century should be interesting.

The “Mainstream” Interpretation

In Chapter 7, I constructed an interpretation of Darwin's thoughts on evolutionary progress gleaned from writings (private notebooks, unpublished manuscripts, published works, correspondence) spanning some twenty years. I argued that, based on the available evidence, it must be concluded that Darwin was a committed progressionist, in the qualified sense there explained. And yet, the question of Darwin's real view of evolutionary progress has been a contentious issue amongst scholars. The problem arises for two reasons. First, at times Darwin does indeed sound like a committed progressionist, whereas at other times he sounds positively scornful of the very idea. Unless Darwin was flat-out inconsistent (or just plain confused), some explanation of this disparity must be offered. Second, because “progress” is a noxious concept for many contemporary biologists (and historians), they find it incredible that Darwin himself took the idea seriously, or perhaps even embraced it enthusiastically. In support they can offer the following argument: The principles of Darwin's theory provide no justification for the belief in evolutionary progress. Surely Darwin himself realized this. Therefore he could not really have believed in it, his occasional (apparent) endorsements of progress notwithstanding.

I attempted to resolve the first of these two problems by arguing that in interpreting Darwin's view it is important to take chronological considerations into account (Darwin's view changed as his ideas developed), as well as the range of distinctions Darwin was careful to make in working out his own view (e.g., contingent vs. necessary evolutionary progress).

Introduction

The two most striking facts about the living world that Darwin attempted to explain were that organisms are so often superbly fitted for survival and reproduction, and that living things display a staggering diversity of different forms. In principle, the two facts could be explained independently of one another (as Lamarck believed they should), but if a significant part of the explanation of the latter fact is that species have diversified in the course of adapting to different environmental challenges, then adaptation becomes the central Darwinian concept for explaining both good design and diversity. Familiarity with the career of adaptationist explanations, therefore, becomes critical to understanding the evolution of Darwinism.

As we saw in the previous chapter, Darwin's view of adaptation underwent a significant shift from his earlier view (influenced by theological considerations) that organisms were perfectly designed, to his later view (developed in light of his understanding of the operation of natural selection) that organisms are at best only relatively well adapted to their circumstances. As Darwin was moving from a notion of absolute to a notion of relative adaptation, his ally and intellectual sparring partner Alfred Russel Wallace was becoming a strict selectionist-adaptationist for whom every feature of every organism (with one notable exception, to be discussed in Chapter 10) has resulted from present or past utility.

Introduction

Natural selection operates by favoring those individuals whose characteristics confer any slight advantage in what Darwin termed “the struggle for existence.” As selection operates generation after generation, distinguishing the fit from the less fit, adaptations evolve and are passed on to offspring, which in turn engage in the struggle anew, resulting in “the improvement of each organic being in relation to its organic and inorganic conditions of life” (Darwin 1859, p. 84). Hence the astounding array of complex adaptations characterizing living things. On this all evolutionists agree.

Darwin maintained again and again that “natural selection works solely by and for the good of each being” (Darwin 1859, p. 489; 1959, p. 758). But there are many “beings” involved in the evolutionary process. By whose and for whose “good” does natural selection work? As we have seen, although Darwin generally thought of selection as operating on and for the good of organisms (i.e., as improving the adaptations characterizing the individual organisms constituting an evolving lineage), when the situation warranted it he was also willing to countenance selection operating and forging adaptations at the level of communities or groups.

Listen to Your Mother

In later life the eminent physiologist Sir Charles Sherrington recalled that, as a young man in 1873, as he was departing his home for a summer holiday, his mother persuaded him to take along a copy of the Origin of Species, saying “It sets the door of the universe ajar!” (quoted in Young 1992, p. 138). Sherrington's mother was right. No other scientific theory has had such a tremendous impact on our understanding of the world and of ourselves as has the theory Charles Darwin presented in that book.

This claim will undoubtedly sound absurd to some familiar with the history of science. Surely the achievements of Copernicus, Galileo, Newton, Einstein, Bohr, and other scientists who developed revolutionary views of the world are of at least equal, if not greater, significance. Aren't they? Not really. Although it is true that such scientific luminaries made fundamentally important contributions to our understanding of the physical structure of the world, in the final analysis their theories are about that world, whether or not it includes life, sentience, and consciousness.

Introduction

Recall once more Darwin's claim, the exploration of which is the central purpose of this book: “As natural selection works solely by and for the good of each being, all corporeal and mental endowments will tend to progress towards perfection” (Darwin 1859, p. 489; 1959, p. 758). In previous chapters we have examined the themes of “selection, perfection, and direction” as they pertain to living things in general, very few of which could be said to have impressive “mental endowments.” Natural selection in conjunction with various chance elements operates on a range of causally interconnected biological entities, resulting in striking evolutionary trends and astounding (but ultimately imperfectly designed) living things. Such is Darwinian orthodoxy, at least concerning the physical evolution of nonhuman living things. But what about human beings and their most distinctive characteristic – intelligence? What does (or might) Darwinism say about us? In particular, how might the evolution of intelligence figure in a Darwinian understanding of life?

In this chapter, we will look at the past, present, and future of Homo sapiens, as viewed through Darwinian perspectives, and in so doing connect the themes of selection, perfection, and direction in evolution as applied to our own species. A range of additional questions present themselves for our consideration. How did Darwin treat the evolution of human “corporeal and mental endowments”?

Introduction

“After having been twice driven back by heavy south-western gales, Her Majesty's ship Beagle, a ten-gun brig, under the command of Captain Fitz Roy, R. N., sailed from Devonport on the 27th of December, 1831” (Darwin 1839, p. 1). So begins Darwin's travel journal, The Voyage of the Beagle, published in 1839. The purpose of the expedition was to survey the South American coast and to make chronometrical measurements. The twenty-two-year-old Darwin had signed on as (unofficial) ship naturalist and (official) “gentleman dining companion” for the captain. The expedition was planned as a two-year voyage. In fact, it would be nearly five years before the Beagle returned to England (29 October 1836). Its voyage proved to be the seminal experience in Darwin's life.

A Theory by Which to Work

The story of Darwin's discovery of “evolution by means of natural selection” has been told many times (e.g., Bowler; 1989; Young 1992). Although scholars continue to debate the relative importance of one or another element in this story, there is nonetheless widespread agreement on the basic factors that led Darwin to his theory.

Introduction

Darwin viewed the evolutionary process as contingently but nonetheless significantly progressive. Under the influence of natural selection organisms become not only better adapted to their conditions of life, but also tend to become more complex and specialized – more improved, in a sense. The synthesis of Darwin's ideas with Mendelian genetics in the first half of the twentieth century resolved many of the problems that led some biologists immediately after Darwin to embrace non-Darwinian evolutionary theories. Ironically, such developments also exacerbated the problems posed for the idea of evolutionary progress. If evolution simply consists of shifts in gene frequencies resulting from selection operating on randomly generated mutations in fluctuating environments, in what sense could the evolutionary process as a whole be considered “progressive”? Different biologists responded to this problem in different ways. The result was a sustained controversy over the meaning and reality of evolutionary progress, the terms of which continue to inform contemporary debates on this issue.

In considering the controversy over evolutionary progress in the twentieth century, I will focus on two debates that serve to highlight the critical biological and philosophical issues involved. The first occurred in the middle decades of the twentieth century and pitted against one another two of the most prominent evolutionists of the day.

Introduction

In order to explain certain puzzling biological phenomena that seemed to make little sense on the assumption that natural selection operates exclusively at the level of individual organisms, Darwin toyed with the idea of selection operating at the level of entire communities. The implications of this idea were profound. If selection operated at this more inclusive level, then the “beings for whose good natural selection works” might include groups as well as individual organisms. Selection operating at the group level could forge adaptations that benefit the group rather than each organism considered separately. Consequently, not every property of an individual organism need benefit that organism. Indeed, some organismic properties might even be detrimental to their immediate possessors, so long as they were sufficiently advantageous at the group level. Thanks to Darwin's invocation of community-level selection, for any biological phenomenon or characteristic requiring an evolutionary explanation, one could now ask whether it was selected and had thereafter evolved for individual or for group benefit.

Darwin's bold move of introducing the idea of selection for group benefit significantly expanded his theory's ability to explain puzzling biological phenomena. It also created a troubling tension within his theory.

Introduction

Writing in the eighteenth century, the Scottish philosopher David Hume was duly impressed by the order, harmony, and apparent design of the natural world. It seemed to him, as it did to the vast majority of his contemporaries, to be a world that bespoke the activity of a wise Deity who arranged its various parts to function together with awe-inspiring precision. Then, as now, the most impressive instances of nested sets of machines within machines were living things, in comparison with which whatever other “machines” the universe consists of pale in comparison.

Hume could not have foreseen how much more detailed our knowledge of living things would become in the following two centuries. We now understand, in ways Hume could have only dimly imagined, how intricately adapted these living machines are to their environments. With such marvelous adaptations in abundance, it is hard not to be impressed. But exactly how impressed should we be? Reflecting on Hume's remark, Cronin (1991, p. 23) asks exactly the right question: “Adaptations, in Hume's delightful phrase, ‘ravish into admiration all men who have ever contemplated them’. But how ravishing, how perfect should we expect them to be?”

Introduction

Considered as a whole, the two most striking aspects of the evolution of life on earth are the staggering diversity of living forms that have come into existence, and the fact that older forms have given way to new and improved forms that seem (for the most part) to be admirably adapted for their respective ways of life. Darwin captured both aspects of evolution in the closing words of the Origin, where he remarked that “from so simple a beginning, endless forms most beautiful and most wonderful have been, and are being, evolved” (Darwin 1859, p. 490). Although there are fascinating problems associated with the evolution of diversity (for example, why are there so many different kinds of living things? How do new species come into existence? What are “species,” anyway?), it is the second aspect of the evolutionary process that is at issue here. Life has not only diversified from its initial humble beginnings, it has also advanced. Multicellular organisms (“metazoa”) arose from unicellular organisms; mammals arose from earlier, nonmammalian ancestors; and in general larger and more complex organisms arose from smaller and simpler ones.

Introduction

It would be difficult to find a more optimistic expression of the power of natural selection to shape living things to any imaginable degree of biological perfection. Such claims abound in Darwin's writings. Consider the famous closing words of the Origin: