Sep 18 2024
Charles Darwin’s keen observations of the natural world famously yielded predictions about its inner workings, many now considered to be far ahead of their time. Known today as the “Father of Evolution,” Darwin rightly theorized in his 1859 book On the Origin of Species that evolution occurs as a result of natural selection, a process in which individuals better adapted to their environment survive and pass on their genes to the next generation, allowing species to evolve over time (Taylor et al., 2022).
One of Darwin’s most famous predictions—regarding the stunning Madagascar Star Orchid (Angraecum sesquipedale)—serves as evidence of the process we now know as coevolution, in which the evolution of one species influences another (Ridenhour, 2014). In 1862, upon receiving a specimen of A. sesquipedale collected in Madagascar by a fellow naturalist, Darwin took immediate note of the orchid’s foot-long ‘nectar spur’, which holds nectar at its very bottom. Darwin hypothesized that in order for the orchid to be pollinated, there must be an insect with a proboscis long enough to reach the bottom of the spurs (Johnson & Anderson, 2010). As such an insect had never been seen before, Darwin’s prediction garnered ridicule. However, Alfred Russel Wallace, another renowned British naturalist credited with developing the theory of evolution independent of Darwin, supported this prediction in his 1867 book Creation by Law, writing, "that such a moth exists in Madagascar may be safely predicted, and naturalists who visit that island should search for it with as much confidence as astronomers searched for the planet Neptune,—and they will be equally successful" (Askham, 2021).
And successful they were! In 1903, two scientists first observed what came to be known as Wallace’s sphinx moth (Xanthopan praedicta), the most recent specimen of which has a tongue measuring a whopping 11.2 inches—the longest of any insect in the world (Shersby, 2023). This case for coevolution was closed, two decades after Darwin’s death. Moths with a longer proboscis are better adapted to reach the nectar of A. sesquipedale, while orchids with longer nectary spurs had a better chance of being pollinated by visiting moths (Johnson & Anderson, 2010). These two unique species are the result of an evolutionary arms race that influences many other plant-pollinator relationships in nature. You can see a live specimen of the endangered Madagascar Star Orchid in the New York Botanical Garden’s Enid A. Haupt Conservatory.
The writing of this story made possible through a National Science Foundation digitization grant (award # 2223881) Digitization and Enrichment of U.S. Herbarium Data from Tropical Africa to Enable Urgent Quantitative Conservation Assessments
References:
Askham, B. (2021). Moth predicted to exist by Darwin and Wallace becomes a new species. Retrieved 29 July 2024, from https://www.nhm.ac.uk/discover/news/2021/september/moth-predicted-to-exist-by-darwin-and-wallace-becomes-a-new-species.html
Johnson, S.D., Anderson, B. (2010). Coevolution Between Food-Rewarding Flowers and Their Pollinators. Evo Edu Outreach 3, 32–39. Retrieved 29 July 2024, from https://doi.org/10.1007/s12052-009-0192-6
Ridenhour, Benjamin J. (2014). Coevolution. obo in Evolutionary Biology. Retrieved 29 July 2024, from https://doi.org/10.1093/obo/9780199941728-0023
Shersby, M. (2023). Wallace’s sphinx moth: The long-tongued insect predicted by Darwin decades before it was discovered. Retrieved 29 July 2024, from https://www.livescience.com/animals/wallaces-sphinx-moth-the-long-tongued-insect-predicted-by-darwin-a-century-before-it-was-discovered
Taylor, A.P. Than, K., Garner, T. (2022). What is Darwin's Theory of Evolution? Retrieved 29 July 2024, from https://www.livescience.com/474-controversy-evolution-works.html
