Cultivating a New Tree

Carolus Linnaeus, born in a turf-covered house in Sweden in 1707, transformed botany from a collection of medieval folklore about healing herbs into a modern science. High school students today still study his “tree of life,” a method of classifying plants and animals based on their structural and functional similarities.

What their textbooks don’t say is that Linnaeus came to doubt his own scheme, lamenting late in life that it was marred by an overreliance on superficial appearances. Sure enough, a century after Linnaeus drew his tree, Charles Darwin showed how the botanist had been misled by “mimicry,” the evolutionary process wherein different plants and animals embrace similar biological solutions--like the black-and-yellow “jackets” that both bees and wasps wear to deter predators, despite their dissimilar genetic makeup.

Now, two new studies offer the strongest evidence yet that you can’t judge a creature by its cover. Research released last month at an international botany conference in St. Louis, along with a study by British scientists to be published Monday in the journal Genome Research, redraws Linnaeus’ tree. Having found striking differences in the genetic makeup of species that Linnaeus had grouped together, the researchers categorize plants into three separate kingdoms and move fungi-like mushrooms and toadstools out of plants altogether and into a kingdom of their own. Astonishingly, these fungi turn out to be genetically closer to humans than to plants.

Linnaeus’ classification scheme became popular not because it captured some ineluctable truth about nature. Rather, by the botanist’s own admission, the system divided species based more on intuition than science, much as an art historian might group paintings into schools. Some historians argue that Linnaeus’ tree became popular simply because it met the social needs of his day--particularly the eagerness of a nascent scientific era to bring order to nature and the belief of his aristocratic patrons that his Latin-based system of naming would aid their efforts to supplant languages with a common mother tongue.

The new studies, stemming from an international plant genome research project called Deep Green, also are influenced by social needs. Agricultural and pharmaceutical industries have supported Deep Green in hopes of profiting from its successful effort to decode the first plant genome: that of a tiny flowering mustard plant called Arabidopsis. And profit they have. While the decoding won’t be completed for another year, early insights have already allowed manufacturers to genetically modify plants to absorb toxic elements like mercury from the soil, produce compounds necessary for manufacturing biodegradable plastics and create more nutritious crops.

Deep Green was created to meet social needs, but its basis in genetic mapping makes it more scientific and less cultural than the scheme of Linnaeus. While the old tree was used to expand the influence of one language, Latin, the new tree seeks to decode the universal language of life, DNA. And while the old tree tried to detect differences in species, the new tree seeks to find their common ancestor: the single, primordial “Eve” whose genes are in us all.