Complexity at large

The following news item is drawn in part from a news article in the 17 April 2003 edition of Science Express titled “Diverse Plant and Animal Genetic Records from Holocene and Pleistocene Sediments,” by Eske Willerslev et al. Retrieval of ancient DNA is vital to the premise of the movie Jurassic Park and has caused a good deal of excitement as samples of DNA have been purified from sources such as museum specimens of extinct species or frozen mammoths. Reporting in the online version of Science magazine, a large group of scientists led by Eske Willerslev of the University of Copenhagen have announced that they have found a way of performing DNA surveys that capture the diversity of ancient ecosystems. The technique relies on types of DNA common to all plants (chloroplast DNA) or all animals (mitochondrial DNA). Amplifying DNA extracted from Siberian permafrost and sediment in temperate caves in New Zealand has yielded samples from 48 different plant families and a number of types of animals. The Siberian samples include DNA that matches samples extracted from preserved megafauna such as mammoths, bison, and primitive horses as well as trees, shrubs, and mosses. The New Zealand samples include DNA from two extinct species of moa as well as many plants. While much of the DNA retrieved does not match samples from any sequenced organisms, mitochondrial and chloroplast DNA is routinely used to build evolutionary trees permitting good estimation of the approximate type of animal or plant for many of the sequences. To prevent contamination of the samples, the researchers preemptively contaminated the area where the samples were gathered with an easily detected bacterium so that, if contamination protocols failed, that bacteria would serve as a marker for contaminated samples. As an additional safeguard, samples were split and DNA extraction performed by two independent labs. The oldest DNA retrieved was many hundreds of thousands of years old. That sufficient DNA could survive to be detected after this amount of time is a very pleasant surprise. The new techniques will open whole new vistas for students of ancient life. Amplifying DNA from preserved soil will provide whole-ecosystem sampling of the animals and plants present during the time the soil from which the samples were taken was laid down. The diversity of the Holocene Siberian ecology has already been demonstrated to be substantially greater than previously thought. As our current ecosystems bend and break under the strain of human impact, pictures of past ecosystems might prove not only a fascinating study but also a useful source of perspective.