Project Overview :
Natural selection from the gene up: The work of Elizabeth Dahlhoff and Nathan Rank
by the Understanding Evolution team
The evidence that natural selection shapes life on Earth is overwhelming. We see it everywhere in nature: from the pure white fur of the Arctic fox that provides camouflage in its frosty home, to the fluted body of the barrel cactus that allows it to stockpile water in the arid desert. Such adaptations are almost as elegant as natural selection itself. Natural selection is the inevitable outcome of the basic characteristics of life: 1) inheritance — that organisms pass traits on to their offspring, 2) variation — that some of these traits vary from individual to individual, and 3) selection — that some traits allow an organism to reproduce more than others. In any system with inheritance, variation, and selection, the process of natural selection will necessarily occur over time and produce organisms with adaptations. The elegant beauty of natural selection, along with all the supporting evidence we see in nature, explain why biologists accept natural selection as a key process of evolution. And yet, examples of adaptation that are fully understood at all levels—from their genetic basis, up to how they play out in the wild — are rare. That's because convincingly demonstrating natural selection in action is a feat, requiring a combination of lab work and field work, as well as knowledge and skills from a variety of biological disciplines.
Left to right: Professor Elizabeth Dahlhoff, photo courtesy of Elizabeth Dahlhoff; Adult willow leaf beetles on willow tree, photo by Nathan Rank; Professor Nathan Rank, photo courtesy of Nathan Rank
Elizabeth Dahlhoff and Nathan Rank have spent the last 20 years working out one of these rare examples, in an unassuming but intriguing insect, the willow leaf beetle, Chrysomela aeneicollis. This insect lives in cool climates in western North America, including high in the Sierra Nevada mountain range, where Elizabeth and Nathan study them. The results of their investigations not only provide a clear picture of how natural selection operates right now, right outside, but also how wild places will be transformed in the future as they are increasingly impacted by human-caused climate change.