How a team of scientists proved a theory wrong … with snails

A snail in the lab of TEDxPlymouthUniversity speaker John Spicer

A snail in the lab of TEDxPlymouthUniversity speaker John Spicer.

Some popular ideas, despite being proven wrong, continue to thrive in popular culture, academic literature, and even in school courses. Why? Says TEDxPlymouthUnivesity speaker John Spicer of one such idea — it tells “a fantastic story.”An idea that wraps up complex, difficult to understand parts in an elegant narrative is hard to let go, the marine biologist explains in his talk, proceeding to tell the story of 19th-century biologist Ernst Haeckel’s theory of recapitulation, a theory that claims animals go through the steps of their evolutionary history while in development.

The problem? Evidence shows this is not true. Evolution is a lot more tricky than an instruction manual that follows step one, step two, step three, step four, every single time. In his talk at TEDxPlymouth, Spicer shares how Haeckel’s recapitulation is debunked with some little creatures – freshwater snails.

To do this, his team at Plymouth Univesity watched more than 200 snails develop from fertilized egg to matured adult.

A freshwater snail develops under the watchful eye of biologists.

A freshwater snail develops under the watchful eye of biologists.

Through close observation, they found that these animals do not relive their evolutionary history in the short time between conception and development and, unlike Haeckel’s theory, they experience intricate maturation that varies greatly from snail type to snail type. One example Spicer cities is the formation of two hearts to power separate processes at the embryonic stage of one snail’s life, which proves complexity at one of the earliest phases in development. Even other closely related species of snail – 17 across 13 different species – develop differently, they found.


The different ways similar snails develop.

A developing snail's two hearts beat

A developing snail’s two hearts beat.

“You can’t say that ancestral creatures like this had two hearts,” Spicer says. “There’s novelty there and there’s complexity there, even at the earliest parts of development.”

Further studies showed that under stressed conditions, a snail will change up its usual manner of maturation.

This is not to say that 21st-century snails have nothing in common with their evolutionary ancestors, Spicer says, but just that the way snails (and other animals) develop is not as simple as one might like it to be. Recapitulation is a great story, says Spicer, but that’s all. Because in terms of the breadth of the animal kingdom, the evidence doesn’t match up.

Watch his whole talk below:

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