Using Paleontology to Explore the Geography of Plants and Animals

In a very readable, one could even say fast-paced, text, Dennis McCarthy melds paleontology and geology to explain the geography of plants and animals. If you have not been astonished at these distributions, you will be once you get into this book. McCarthy, a research associate of the Buffalo (NY) Museum of Science, begins with the adventurous nineteenth-century naturalists Darwin, Alfred Russell Wallace, and, at the turn of that century, Alfred Wegener. Darwin and Wallace, of course, made pristine collections of both living and fossil organisms from a variety of habitats and deduced that natural selection operated on the survival of populations much as familiar agricultural breeding operated on livestock and crops. Wegener proposed that the interesting jigsaw puzzle fit of the Atlantic coasts of Africa and South America resulted from these continents drifting apart, over millions of years, from a parent landmass. Most geologists and paleontologists, convinced of the immobility of great land masses, denounced this. Wegener perished in a blizzard on the Greenland ice cap while collecting meteorological data. Decades later, with vast amounts of data on the seafloor gathered for World War II naval movements, the presence of upwelling magma along deep underwater ridges was recognized, providing the mechanism for continental drift and persuading scientists of Wegener’s hypothesis. McCarthy describes the geological history of our continents and their progenitors, Pangaea and especially Gondwana. He explains the difference between deep but narrow straits persisting for millions of years, such as that marking Wallace’s Line off Australia, and wider but relatively shallow seas such as Bering Strait that periodically became land when sea levels fell. These and their reverse, the isthmuses such as Panama that rose to link continents, explain the paleontological record of relatively sudden appearances and extinctions as animals and plants crossed into previously isolated territories. Islands, both in oceans and remnant land habitats, could be golden opportunities for speciation into new niches— Darwin’s famous Galapagos finches—or pressures for smaller size: pygmy mammoths and possibly pygmy hominids on the island of Flores (the recent discovery popularized as “hobbits”). Updating on Darwin’s finches, by the contemporary biologists Peter and Rosemary Grant, indicates another theme: population differentiation can occur through learned behavior, not necessarily genetic changes. Galapagos finches learn their songs from their fathers, and females avoid mating with males singing a “foreign” song; when finches colonize a new location, a variant song may develop and inhibit mating with the ancestral population (p. 53). McCarthy’s last two chapters discuss how biogeographical principles may illuminate human history. Perhaps because I am an anthropologist, these chapters seem to me weaker than the preceding ones on geologic and biological data. McCarthy relies heavily on Jared Diamond in these chapters, accepting (pp. 168–72) Diamond’s argument that Eurasians overcame societies in the southern hemisphere because temperate-latitude Eurasia was initially, at the end of the Pleistocene, stocked with domesticable plants and animals, and communication A. B. Kehoe Department of Anthropology, University of Wisconsin-Milwaukee, P.O. Box 413, Milwaukee, WI 53201-0413, USA