The image before you is known as Darwin’s tree of life. Today, most scientists immediately recognize it as a basic idea in evolutionary theory; yet when Darwin drew it in 1837, it was simply a sketch drawn in an attempt to understand the observations he made on the voyage of the Beagle. Based largely on these and later observations, Darwin published On the Origin of Species in 1859, setting off over 150 years of research and cultural debate around the world. But before publication of that seminal work, he filled notebooks with ideas and sketches like this, attempting to reconcile all he had seen.

For me, the power of this image is that it is a tidy summation of what makes science a beautiful pursuit. The eye focuses immediately on the tree itself, which calls to mind the paradigm shift evolutionary theory caused. However, my favorite part of the image is the phrase “I think” scrawled at the top of the page. The essence of scientific inquiry is the ability to say, “I think”, test that hypothesis, and find the truth of the matter through experimentation. Over one hundred fifty years after Darwin publicly said, “I think”, his idea has been validated time and time again by generations of evolutionary biologists. Even better, however, is that in a time when we sequence whole genomes in a day, scientific revelations (and revolutions!) still begin with the simple phrase, “I think.”

edited by Nicole Carlson and Erinn Brigham

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This article was co-published on the TIBBS Bioscience Blog.

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