He entertained the idea that a caterpillar was one creature and a butterfly was an entirely different beast. Harvey further argued that the cocoon or chrysalis a caterpillar entered during its pupal stage was a second egg in which the prematurely hatched embryo was born again. In 1651 English physician William Harvey published a book in which he proposed that caterpillars and other insect larvas were free-living embryos that abandoned nutrient-poor "imperfect eggs" before they matured. Metamorphosis was so successful that, today, as many as 65 percent of all animal species on the planet are metamorphosing insects. This shift proved remarkably beneficial: young and old insects were no longer competing for the same resources. Between 280 million and 300 million years ago, however, some insects began to mature a little differently-they hatched in forms that neither looked nor behaved like their adult versions. The earliest insects in Earth's history did not metamorphose they hatched from eggs, essentially as miniature adults. By combining evidence from the fossil record with studies on insect anatomy and development, biologists have established a plausible narrative about the origin of insect metamorphosis, which they continue to revise as new information surfaces. Metamorphosis is a truly bizarre process, but an explanation of its evolution does not require such unsubstantiated theories (for a critique of Williamson's hypothesis, see this study). Some scientists have proposed outlandish origin tales, such as Donald Williamson's idea that butterfly metamorphosis resulted from an ancient and accidental mating between two different species-one that wriggled along ground and one that flitted through the air. People have known since at least the time of ancient Egypt that worms and grubs develop into adult insects, but the evolution of insect metamorphosis remains a genuine biological mystery even today.
Imprisoning someone for asserting what today qualifies as common knowledge might seem extreme, but metamorphosis-the process through which some animals abruptly transform their bodies after birth-has long inspired misunderstanding and mysticism. A few years later, Renous recounted his tale to Charles Darwin, who noted it in The Voyage of the Beagle. His claim? He could turn caterpillars into butterflies. In the 1830s a German naturalist named Renous was arrested in San Fernando, Chile for heresy.
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