Alan de Queiroz
Basic Books, 2014
How do species disperse – how do they get from one place to another? This is the kind of question that appears to have a ready answer, but experts can spend a lifetime debating. It’s easy to see birds flying in their migrations, or mammals moving across continents. How did trees get across oceans? How did amphibians get to islands? How did monkeys get to South America? The answer to these questions not only has ramifications to evolution, but to the history of life on Earth. And scientists have been debating them since the beginning of the study of evolution.
Although perplexing and difficult to imagine, before we knew about plate tectonics, ocean crossings were the only possible choice. Darwin did some experiments in seed viability, and a lot of people talked about land bridges that no longer existed.
As we learned more about plate tectonics and the deep past of the Earth, it became obvious that most of the dispersal happened by species being isolated by Gondwana (the supercontinent) breaking up. No ocean crossings necessary. Soon enough, the idea of life as a relic of the Gondwanan break up was pervasive to the point of becoming a truism. Ocean crossings were dismissed as almost magical. The incompleteness of the fossil record was no help: the oldest fossil of a species only tells us how old a species might be; it could have been around for a long time before the unlikely set of events that create fossils happened.
Now, scientists studying the question of dispersal use DNA analysis and the molecular clock to provide new evidence that weighs more strongly in favor of ocean crossings. The molecular clock, despite its limitations, can provide more statistical evidence as to when speciation occurs than the fossil record or any other tool we’ve had to date. This statistical evidence can be combined with improved dating, greater knowledge of the continental positions in deep time, and other evidence to build convincing cases for oceanic dispersal. The hypothesis that monkeys rafted from Africa to South America may not ever be “falsifiable” in the way that mathematics or physics hypotheses are falsifiable, but enough evidence can be built in its favor to show that despite improbability, given enough time, it’s the most likely explanation.
This is the “plot synopsis” version of de Queiroz’s book, and like all plot synopses makes a tapestry into a threadbare towel. In examining the basic question of how life disperses, de Queiroz looks at aspects of the philosophy and history of science, how science is engaged by its practitioners – in the field, in academic journals, and in the realm of personal politics. It looks like there is finally enough agreed-on evidence to provide basis for further research.
This is the kind of science book that I like because it engages me in a subject I had little knowledge of, and thought I had little interest in.
Mirrored from Nature Intrudes. Please comment over there.