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Thursday, June 16, 2005

Reading List: The Ghosts of Evolution

Barlow, Connie. The Ghosts of Evolution. New York: Basic Books, 2000. ISBN 0-465-00552-7.
Ponder the pit of the avocado; no, actually ponder it--hold it in your hand and get a sense of how big and heavy it is. Now consider that due to its toughness, slick surface, and being laced with toxins, it was meant to be swallowed whole and deposited far from the tree in the dung of the animal who gulped down the entire fruit, pit and all. Just imagine the size of the gullet (and internal tubing) that requires--what on Earth, or more precisely, given the avocado's range, what in the Americas served to disperse these seeds prior to the arrival of humans some 13,000 years ago?

The Western Hemisphere was, in fact, prior to the great extinction at the end of the Pleistocene, (coincident with the arrival of humans across the land bridge with Asia, and probably the result of their intensive hunting), home to a rich collection of megafauna: mammoths and mastodons, enormous ground sloths, camels, the original horses, and an armadillo as large as a bear, now all gone. Plants with fruit which doesn't seem to make any sense--which rots beneath the tree and isn't dispersed by any extant creature--may be the orphaned ecological partners of extinct species with which they co-evolved. Plants, particularly perennials and those which can reproduce clonally, evolve much more slowly than mammal and bird species, and may survive, albeit in a limited or spotty range, through secondary dispersers of their seeds (seed hoarders and predators, water, and gravity) long after the animal vectors their seeds evolved to employ have departed the scene. That is the fascinating premise of this book, which examines how enigmatic, apparently nonsensical fruit such as the osage orange, Kentucky coffee tree, honey locust, ginkgo, desert gourd, and others may be, figuratively, ripening their fruit every year waiting for the passing mastodon or megatherium which never arrives, some surviving because they are attractive, useful, and/or tasty to the talking apes who killed off the megafauna.

All of this is very interesting, and along the way one learns a great deal about the co-evolution of plants and their seed dispersal partners and predators--an endless arms race involving armour, chemical warfare (selective toxins and deterrents in pulp and seeds), stealth, and co-optation (burrs which hitch a ride on the fur of animals). However, this 250 page volume is basically an 85 page essay struggling to get out of the rambling, repetitious, self-indulgent, pretentious prose and unbridled speculations of the author, which results in a literary bolus as difficult to masticate as the seed pods of some of the plants described therein. This book desperately needed the attention of an editor ready to wield the red pencil and Basic Books, generally a quality publisher of popularisations of science, dropped the ball (or, perhaps I should say, spit out the seed) here. The organisation of the text is atrocious--we encounter the same material over and over, frequently see technical terms such as indehiscent used four or five times before they are first defined, only to then endure a half-dozen subsequent definitions of the same word (a brief glossary of botanical terms would be a great improvement), and on occasions botanical jargon is used apparently because it rolls so majestically off the tongue or lends authority to the account--which authority is sorely lacking. While there is serious science and well-documented, peer-reviewed evidence for anachronism in certain fruits, Barlow uses the concept as a launching pad for wild speculation in which any apparent lack of perfect adaptation between a plant and its present-day environment is taken as evidence for an extinct ecological partner.

One of many examples is the suggestion on p. 164 that the fact that the American holly tree produces spiny leaves well above the level of any current browser (deer here, not Internet Exploder or Netscrape!) is evidence it evolved to defend itself against much larger herbivores. Well, maybe, but it may just be that a tree lacks the means to precisely measure the distance from the ground, and those which err on the side of safety are more likely to survive. The discussion of evolution throughout is laced with teleological and anthropomorphic metaphors which will induce teeth-grinding among Darwinists audible across a large lecture hall.

At the start of chapter 8, vertebrate paleontologist Richard Tedford is quoted as saying, "Frankly, this is not really science. You haven't got a way of testing any of this. It's more metaphysics."--amen. The author tests the toxicity of ginkgo seeds by feeding them to squirrels in a park in New York City ("All the world seems in tune, on a spring afternoon . . ."), and the attractiveness of maggot-ridden overripe pawpaw fruit by leaving it outside her New Mexico trailer for frequent visitor Mrs. Foxie (you can't make up stuff like this) and, in the morning, it was gone! I recall a similar experiment from childhood involving milk, cookies, and flying reindeer; she does, admittedly, acknowledge that skunks or raccoons might have been responsible. There's an extended discourse on the possible merits of eating dirt, especially for pregnant women, then in the very next chapter the suggestion that the honey locust has "devolved" into the swamp locust, accompanied by an end note observing that a professional botanist expert in the genus considers this nonsense.

Don't get me wrong, there's plenty of interesting material here, and much to think about in the complex intertwined evolution of animals and plants, but this is a topic which deserves a more disciplined author and a better book.

Posted at June 16, 2005 16:01