RESEARCH:: Celebrating Darwin
Natural History Collections and Evolution
By Dr. Jeremy J. Kirchman
DNA-based techniques are revolutionizing many long-standing hypotheses of bird relationships.When I reflect, 200 years after his birth, on the revolutionary work of Charles Darwin, I am struck by the important connection between the origin of modern evolutionary biology and the growth of natural history museum specimen collections. It’s no mere coincidence that Darwin and his colleague Alfred Russel Wallace discovered the principle of natural selection after years of working as museum specimen collectors. It was the act of collecting and comparing specimens from many places that led both men to the conclusion that all species are descended from a common ancestor through an evolutionary process of lineage splitting.
In their efforts to document the full range of biological diversity, Victorian Era specimen collectors were not looking for evidence of evolution. As specimen collectors in the Victorian Era tried to document the full range of biological diversity, they were not looking for evidence of evolution. But as natural history collections grew and larger series of specimens could be compared, it became clear that members of a species often look slightly different in different places, and that in some cases it’s very hard to tell where one species ends and the next one begins. Before this era of exploration, it was easy to think that species never change, and that sharp boundaries separate each species from all the others. The emerging pattern of geographic variation forced scientists to explain how populations adapt to local conditions and eventually diverge so far from other populations that they become distinct species. Darwin and Wallace provided the answer: natural selection.
Understanding the origin of new species remains one of the central goals of evolutionary biologists, many of whom still study patterns of variation in natural history collections. As curator of birds at the New York State Museum, I split my time between conducting research on geographic variation in bird populations and curating the collection of nearly 20,000 bird specimens. On the research side, I make use of recent advances in DNA technology that allow me to directly examine genetic variation in natural bird populations. I am especially interested in measuring the amount of genetic divergence among geographically isolated populations, such as those found on islands or on mountaintops. Ornithologists define bird species as groups of individuals that can exchange genes by interbreeding. Thus the central question of my research concerns the extent to which birds from isolated populations exchange genes.
On the curatorial side, I manage our growing bird collection, preparing, identifying, and cataloging each new specimen. When I assign a specimen to a species, I’m making a hypothesis regarding the evolutionary relationships of that bird. Like all scientific hypotheses, these curatorial decisions are subject to further testing as new information and techniques become available. Today, DNA-based techniques are revolutionizing many long-standing hypotheses of bird relationships, and one of my most important tasks as curator is to preserve a small tissue sample from each new specimen as a genetic archive for future research. As both a researcher and specimen collector, I follow the path laid down by Darwin of studying evolution and of building a collection that will inform our better understanding of evolution for generations to come.
Dr. Jeremy J. Kirchman is the curator of birds at the New York State Museum.