habitats—from the human stomach to more than a mile underground—where conditions were thought to be too harsh to allow life. New birds, plants, and mammals are still found with some regularity. Entomologists name and describe new insect species at a rate of about 1,500 per year. The evidence that some genes have been conserved throughout evolution and the availability of polymerase chain reaction to survey those genes made it possible to begin exploring the diversity of the microscopic world. Suddenly, tiny organisms that appeared under the microscope to have only a few basic and uncomplicated body forms were revealed to be unimaginably diverse—in fact a new kingdom of life, the Archaea, was discovered to be as different from bacteria as bacteria are from eukaryotes (Woese et al., 1990). The advent of high-throughput sequencing and sophisticated computational analysis has allowed biologists to begin to plumb the diversity of the microbial world, and it appears that life at the microscopic level is vastly more diverse than biologists ever imagined. A recent survey of microbes in the ocean using an approach called metagenomics not only revealed thousands of previously unseen genes but hundreds of novel protein families. Families of proteins that were already known, like the rhodopsins that absorb light in the human retina, were found to have hundreds of distinct members in the ocean sample (Bejà et al., 2000, 2001). The vast numbers of new genes are not necessarily mere variations on known themes; the potential functional diversity—in other words, proteins and synthetic pathways that carry out currently unknown reactions—to be found in microbial communities is enormous (e.g., Venter et al., 2004; Zhang et al., 2006; Gill et al., 2006).

What is the significance of discovering one more beetle, one more bacterium, or one more protein? One answer lies in the incredible diversity of functions that evolution has generated. Nature has foreshadowed our technical developments, and functional biodiversity can be a fertile source of ideas for technology. For example, a group of neuroscientists has found a parasitic fly that can locate the sounds of its hosts—field crickets—with unparalleled accuracy. Remarkably, the fly’s ears are tiny and only one-half millimeter apart (Mason et al., 2001). The fly’s ears have inspired the design of directional microphones and a new generation of directional hearing aids. Another example is a group of brittlestars (relatives of sea stars) that have turned their skeletons into a visual system made up of arrays of microscopic lenses (Aizenberg et al., 2001). The lenses detect light and allow the animals to find dark hiding places on the ocean bottom. Such small lenses are beyond current human engineering capability. However, their precisely curved shape and the way they are arrayed are prompting engineers to create novel optical devices.

Recognizing that nature provides a vast toolbox is only one motivation for studying life’s diversity. The complex interconnected web of living species is critical to human life. Humans depend on the living world in count-

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