The Tangled Tree: A Radical New History of Life

by David Quammen

Such people, all contributors to a scientific upheaval, are of additional interest for the ways their works grew from their lives. They serve as good reminders that science itself, however precise and objective, is a human activity. It’s a way of wondering as well as a way of knowing. It’s a process, not a body of facts or laws. Like music, like poetry, like baseball, like grandmaster chess, it’s something gloriously imperfect that people do. The smudgy fingerprints of our humanness are all over it.

Many are called, but few are chosen. The book that awakened Darwin to this reality was An Essay on the Principle of Population, by a severely logical clergyman and scholar named Thomas Malthus.

Margulis was a forceful young woman from Chicago.

That was only a temporary setback for such a determined young woman.

At the end of the paper, they cited Lynn Margulis. They cited Merezhkowsky. They thanked Carl Woese for “advice, encouragement, and much unpublished data.” Doolittle might also have thanked Woese—and probably did, more privately—for exporting his methodology to Halifax in the person of Linda Bonen.

The concept of “species” is commonly supposed to be secure. It isn’t secure. It’s especially insecure in the realm of bacteria and archaea, but it’s even a bit blurry when scientists try to distinguish one species of plant or one species of animal from another. The boundaries blur. The edges are as porous as Goretex—or, in some cases, as cheese cloth. One reason for the blur, one symptom of the porosity, is horizontal gene transfer—genes moving sideways instead of just downward from parent to offspring. If genes cross the boundary between one species of bacteria and another, then in what sense is it really a boundary?

Researchers at the time were so reluctant to believe that bacterial genes could be transferred into animal genomes that, before publishing a new genome sequence, they routinely edited out the bacterial stretches.

Among such simpler microbial creatures, they wrote, horizontal gene transfer is far more important, in quantity and consequences, than imagined previously. Its impacts could be understood in four ways. First, new genes received by sideways transfer, from a different lineage or species, may allow a population of microbes (the recipient bug and its offspring) to colonize an entirely new ecological niche. Second, it may allow organisms to acquire a new sort of adaptation abruptly, without passing through the dangerous stage of being only half adapted to one situation or another. Third, this transformation happens fast compared with incremental mutation, which proceeds slowly. Fourth, HGT is a “font of innovation,” bringing drastically new genetic possibilities, new supplies of variation, on which natural selection can act. All four kinds of impact are interrelated and represent overlapping perspectives on the same phenomenon.

and a lively wife, Bernadette Pace, who had her own doctorate in molecular biology.

Mammals do it too, sometimes. “The cells that make up our bodies have also not arisen gradually in the typical Darwinian manner of gene mutation and natural selection.” Some of the changes occurred by quantum leaps. Our mitochondria came aboard suddenly, deep in the past of our eukaryote or pre-eukaryote lineage, as captured bacteria. Plants acquired their chloroplasts the same way. Our genomes are mosaics. We are all symbiotic complexes, even us humans.

It would have been logical at the time, the late 1980s, when Heidmann established his own lab, for a scientist such as he with an interest in retroviruses to launch a research program on HIV-1. The money would have flowed, the significance was vast and urgent. Instead, he did something less obvious.