The Long View

Natural History, Sept, 2001 by Ellen Goldensohn

Living on the paved island known as Manhattan, some of my encounters with nature necessarily take place on sidewalks. I once followed a giant silk moth for several blocks along Amsterdam Avenue in broad daylight. On a spring morning several years ago, I saw a tiny ovenbird that was walking north on Park Avenue, probably exhausted by its migratory flight from South America. And I routinely glimpse house mice frolicking in the median strip along upper Broadway after dark.

But most of my observations of plants and animals (not counting carpet beetles, silverfish, and cockroaches) take place in public parks and gardens. A favorite stroll in Riverside Park takes me past a row of honey locust trees. Long ago, I noticed that their trunks (beginning about eight feet above the ground) were encircled with three- to five-inch-long, needlelike thorns.

I'd never given the thorns a thought, however, until Connie Barlow, a writer and independent scholar of evolution, came to the magazine's office to propose a story on "anachronistic fruits." Barlow explained the intriguing idea that many puzzling features of North American plants--the huge pit of the avocado, the indigestible flesh of the Osage orange, the outrageous thorns of the honey locust--evolved as either enticements to or defenses against large animals that are now extinct.

In 1925, excavations for an apartment building in northern Manhattan turned up a lower jaw, some teeth, and one limb bone from Mammut americanum, the American mastodon. For millions of years, until about 10,000 years ago, these elephants doubtless walked where I now walk in Riverside Park, and their appetite for the honey locust's seed pods may have had a role in the evolution of the tree's ferocious thorns.

Thinking about nature in evolutionary terms--a point of view that's common in the pages of a natural history magazine but rare in other venues--gives one a marvelously long view and some unusual insights into why things are the way they are. Once upon a time, ground sloths or camels or even ancestral rhinoceroses may have inhabited your part of the country. Reading Barlow's "Ghost Stories From the Ice Age" (page 62) makes one think about such things.