Charles Darwin had been mulling over his observations of and theories about natural selection for years, but what finally prompted him to write On the Origin of Species by Means of Natural Selection (published November 24, 1859) was the arrival of a letter from fellow naturalist Alfred Russel Wallace (1823 to 1913) on the very same subject. This fateful 1858 letter, Darwin noted in communication with geologist Charles Lyell, was a most "striking coincidence. If Wallace had my M.S. sketch written out in 1842 he could not have made a better short abstract."

To commemorate this meeting of the minds and the 150th anniversary of Darwin's seminal work, the American Museum of Natural History in New York launched the first public viewing of Wallace's most substantial remaining collections: a single cabinet packed full with 1,679 well-preserved natural specimens collected, pinned, labeled and arranged, experts believe, by Wallace's own hands. The cabinet belongs to Robert Heggestad, who spotted it in an antique store in 1979.  

Like Darwin, Wallace spent years in the field, traveling to far-off locales and studying the similarity and differences among species. Much of Wallace's formative fieldwork took place in the wilds of Brazil, where he worked from the 1850s to 1860s with entomologist Henry Walter Bates. Wallace's later travels to Indonesia further allowed him to carefully study animals directly and helped to solidify his theories about how species came to differentiate.

Assembled in the fashion of the times, many of the collection's drawers are constructed with a bottom layer of cork overlaid with paper. As the project's lead curator David Grimaldi points out, there are few—if any—errant pin holes in the paper, leading him and others to presume the collection's arrangements are original to Wallace: "You're looking at the mind of the naturalist," says Grimaldi, an entomologist in the museum's Division of Invertebrate Zoology.

Even though the provenance of the collection remains murky—having been found in an unclaimed baggage lot in Philadelphia in the 1960s—historians have analyzed everything from the handwritten tags to the structure of the pins used to hold insects in place and assert that it is unlikely to have belonged to any other than Wallace himself. The cabinet also appears to be built to specifications Wallace described in writings to Bates, his colleague and collaborator, with tight drawers and slots built into them to hold fumigants to keep unwanted bugs at bay.

From butterflies to botanical samples, the rosewood cabinet's 26 drawers hold a range of items that curators think Wallace chose to keep on hand for reference and sentimental reasons, many of them having been collected in his early days as a surveyor in the U.K.

The collection is also of keen interest to many because Wallace held on to so few of the items he picked up in the field—selling most for income and losing much of the finds from his years in Brazil to a shipping accident during his return to the U.K.

So thorough was Wallace's enthusiastic collecting that many of the items in this chest alone promise to be species new to science. One, in fact, was just described by another biologist earlier this year as a new genus, Grimaldi notes. 

As Darwin had his finches, Wallace tuned his theories on evolution based in part on butterflies, paying careful attention to changes in coloration, warning patterns and mimicry. One butterfly in particular, the Papillo agamemnon (a spotted specimen on display in one of the drawers) from Indonesia, featured prominently in Wallace's writings as the "best example" to illustrate the progression from variation to speciation.

By studying beetles, as Darwin also did, Wallace began to understand the pace of evolution. Wallace noted "how insects evolve very, very quickly," Grimaldi says.

Wallace is perhaps best known for his work with biogeography, having given his name to Wallace's Line, an invisible divide which seems to separate the disparate groups of animals on the islands of Borneo and Sulawesi. And aside from accomplished naturalist, Wallace is also remembered as a geographer, anthropologist, spiritualist and one of the earlier scientists to ponder the human impact on the natural world. 

Image of butterflies (including Papilio agamemnon, fourth column, second row) courtesy of R. Heggestad, image of cabinet courtesy of D. Finnin/AMNH, image of beetles and other insects courtesy of R. Heggestad