Barlow isn’t a scientist, but she’s got a scientist in her pocket: Paul Martin of the University of Arizona. In 1982, Martin and Dan Janzen of the University of Pennsylvania published a paper in Science in which they postulated that a lot of the features of some modern plants are best explained by co-evolution with Pleistocene megafauna (mammoths, gomptotheres, glyptodonts, ground sloths, rhinoceroses, horses, etc.). As those animals are now extinct or extirpated from North America, the plants lack their “disperser” partners. As a result, their “over-sized” or “overly-protected” fruits don’t get dispersed, and tend to rot on the ground. Gravity is the main modern dispersal agent, and so they tend to be quite common in floodplains, but not upland areas.
North American examples of these so-called “ecological anachronisms” are honey locust, osage orange, gingko, pawpaw, Kentucky coffee tree, persimmon, and potentially desert gourds. Another great example, from Central America, is the avocado. These plants bear fruits (or fruitlike growths, if they’re not true angiosperms, like the gingko) which are either very large, very tough, or have very large seeds that are not swallowed by modern animals. Barlow claims that these plants are “haunted” by their departed ecological partners, an evocative analogy that gets repeated many times, long after it’s worn out.
The book is interesting and it held my attention. More importantly, it made me look at the trees around me and wonder at the evolutionary forces that sculpted them, forces now absent, though their sculpture remains. These plants surround us, and one you learn to spot them, it’s hard to pass them on the street without pondering their species’ history.
Walking back to my car after structural geology class at George Mason University last week, I saw some of the pods of the honey locust — big leathery things 15 cm long, 3 cm wide, and 1 cm thick. Some had been cracked open by the pounding action of undergraduate footsteps, and I saw inside the green pulp that Barlow described in the book. I remember she described it as “sugary,” so I grabbed an unmolested pod, and stuck it in my bag. That night, at home, my girlfriend and I cracked it open and tried some. It was sweet! Kind of mango-gummy, I’d say. However, the shell is quite bitter, and so if you try it at home, don’t lick the shell. After I accidentally grazed the shell with my lip and then my tongue, I had to spit and rinse my mouth out. It was nasty.
The Ghosts of Evolution isn’t a perfect book. One criticism I would offer is that it’s a bit repetitive, where the original thesis (a fresh, interesting idea) gets beaten into the ground with endless reiteration. Guns, Germs, and Steel fell victim to the same lack of editorial excision, in my view.
Another problem is that Barlow illustrates her plants with a series of “arty” photographs. The composition of these photos is symmetrical and balanced. They convey beauty, but they aren’t really scientific. Also, the sense of scale she provides is a honey locust seed. This may seem an appropriate sense of scale to a North American botanist, but most of us do not have an intuitive sense of the size of a honey locust seed, even if we are told it’s “about 1 cm long.”
Finally, I would say she needs to be more precise about where the science stops and her own enthusiasm for the idea takes over. The desert gourds she discusses are an exemplar of this: She runs with the idea of ecological anachronisms, and tries to apply its principles to a plant she sees in her own New Mexico neighborhood, but it is unclear how much of this discussion is her own extrapolations and how much has been rigorously researched by botanists. On the other hand, she does things that are beautiful without being scientifically significant: like rubbing a honey locust pod over a mastodon tooth in the American Museum of Natural History, and reflecting how that’s probably the first time that’s happened in more than 10,000 years!
All in all, worth reading if you’re into ecology, evolution, the Pleistocene, or botany. Has anyone else read it? If so, what did you think?