A grandmaster surveys the field

What Makes Biology Unique? is Ernst Mayr's 25th book, published in time for his 100th birthday. Although a collection of essays (some of them previously published), it is quite unified, the chapters proceeding logically and connected by cross-referencing. As stated in the preface, this brief tome is a ‘survey of controversial topics in biology.’ These range from classic issues in the philosophy of science (teleology and reductionism) to the history of evolutionary biology and taxonomy, as well as the status of central concepts such as natural selection and biological species.Mayr has little patience for the findings of most professional philosophers. He simply can ‘not understand why most philosophers of science believe the problems of philosophy can be solved by logic,’ and instead advocates an ‘empirical’ approach that examines what biologists have actually done and eschews viewing biology through the reductionist and deterministic lens of the physical sciences. In practice, although the reader is told (in broad terms) what evolutionary biologists and taxonomists have done over the past couple of centuries, Mayr's approach is not so much empirical as conceptual. His favored method is to pose a question (e.g. What is Darwinism?), then proceed by showing that the answer can only be obtained by conceptual parsing (e.g. Darwinism actually consists of five independent theories). This approach is often illuminating, but has definite limitations.I found the chapter about natural selection the most problematic. Mayr argues that natural selection consists of two distinct processes, a culling process wherein the least-fit individuals are eliminated, and a selection process wherein individuals compete for reproductive success. Although he does not use the terms, these two processes correspond to the standard distinction between the mortality and fertility components of fitness, respectively. Mayr goes on to argue that the culling process (which he terms ‘natural selection proper’) only eliminates the worst rather than selecting the best, which explains why evolution is so unpredictable: much variation remains among the ‘less inferior individuals’ who survive, providing grist for ‘aberrant evolutionary trends’ based on sexual selection and chance. By contrast, he says, selection for reproductive success (sexual selection, kin interactions, and the like) does truly select for the best. Mayr never explains why differential survival would be a weaker screen than differential fertility would be, and further clouds the argument by stating that “in a process of actual selection a bird with a cumbersome tail such as that of a peacock would never emerge as ‘the best’”. Mayr goes on to outline his well-known views in favor of the individual (and sometimes the social group) as the object of selection, and against the selfish gene, ‘bean-bag genetics,’ and vehicles or replicators. In a rare allusion to mathematical formalism, he argues that group selection can only occur when resulting from social interactions: ‘the fitness of a group is higher or lower than the arithmetic mean of the fitness values of the composing individuals’. Alas, the clarity of this claim is lost in the following passage stating that ‘such groups often consist of close relatives and such selection is actually kin selection. And kin selection is really individual selection.’Mayr closes with two essays focused on humanity, both written specifically for this volume. One is a whirlwind tour of hominin evolution, cataloguing recent important finds (up through 2002) and offering Mayr's ‘somewhat speculative report of [his] own reinterpretation of human prehistory.’ The final chapter is a trenchant critique of the search for intelligent life elsewhere in the universe, in which Mayr notes the high odds against electronically broadcasting forms arising: after all, it only happened once in 3.5 billion years on this planet, and there were innumerable branching lineages that, in principle, could have produced such an outcome. He uses this critique to return to one of the central themes of the book: the contrasting perspectives of biology (with its emphasis on chance, history and particular events) versus physics and chemistry (with their contrasting reliance on determinism and universal laws).In sum, this is a relatively unified but less than magisterial volume. The prose is workmanlike, pithy and short on subtlety. Mayr's directness is refreshing, but What Makes Biology Unique? offers fewer penetrating insights than the writings of Maynard Smith, and a less engaging style than the best science essayists working today. Yet on topics in which Mayr has been centrally involved, such as the biological species concept and the 1940s neo-Darwinian synthesis, it is a rewarding work that is broadly accessible.