Ghosts of Evolution: Nonsensical Fruit, Missing Partners and Other Ecological Anachronisms (Hardcover)

Connie Barlow thinks these differences are very important. As she reminds us, all those fruits have been around since long before humans confined them to orchards. Winged maple seeds can flit about on the mildest breeze. The avocado, however, clearly needs a little help finding a sprouting site. Before orchardists, who was there to help it reach one? Trees don't like to just drop seeds and hope for the best. Too many seeds in one place results in choking thicket or a sunlight-blocking canopy. The key is dispersal. Leave home, kids, and start life somewhere else. But a rock-sized hunk like an avocado or a honey locust needs a lift. Who gave ancient avocados a ride to a new home?

According to Paul Martin and David Janzen, the carriers were animals who don't exist any more. Barlow follows this pair of researchers who began a new scientific quest by wondering why jungle fruit was rotting under Costa Rican trees. All life struggles to continue through succeeding generations, and lying on the ground covered in fuzz doesn't bode success. Janzen thought there was something missing - an animal that might have conveyed the fruit elsewhere to launch the new generation. As they studied the problem, according to Barlow, they concluded that many fruits and their seeds are living on borrowed time. The animals that helped disseminate seeds for many trees are long extinct.

Barlow belongs at the head of the class for understanding and explaining how evolution works. She shows there's more to the story than tracing single lineages with subtle adjustments in limb, leaf, or mass. Plant life has coevolved with animal species. In developing defenses against animals eating their foliage, plants also needed allies to spread new sprouts. Some seeds travelled with thorns, but others were oversized for that means. Big seeds had to be swallowed, some to be passed intact with dung, but others to initiate the germination process within the gut before passage. All these mechanisms are specific, but the loss of partners have left many tree species vulnerable. Some have "second string" dispersers, but these may not be adequate.

Barlow guides us around the planet and through time, introducing us to trees, their fruits and their likely seed dispersing partners. She reminds us that North America evolved the horse, the camel and a variety of other animals that are either missing or were re-introduced. In those days, the American camel had two sets of incisor teeth. Current Old World camels have a lower set and a hard plate above. New Zealand had no large mammals. Who conveyed the seeds of fifty four species of divaricate plants around the islands? Probably the eleven extinct species of moa native to the islands. Why do some trees around the world have thorns that cease growing above a certain height? There used to be taller animals that could reach the fruits convey them away. Why did the digestive tracts of horses and cows evolve differently? They both eat grass. Barlow examines these and other questions with exquisite style, showing where the evidence shows well and where further work is required. And there is plenty for the young researcher to consider following.

If the findings of the past weren't surprising enough, Barlow's proposals for the future will leave many astounded. Especially farmers and ranchers. Elephants on the Prairies? Camels in Utah [they were there once, why not again?] Hand planted trees where the natural dispersers have disappeared? These are serious questions, because extinction isn't an isolated event. Barlow points out the "cascade effect" engendered by all extinctions. There are many important reasons to read this book. It may amaze you, but be reassured you will not be bored. [stephen a. haines - Ottawa, Canada]