Two souls, alas, are dwelling in the amphibian breast

Tadpoles and frogs evolve as two separate life forms – despite being only one

Children worldwide are mesmerized by the amphibian life cycle as example for the complexity of life forms –  An egg turns into a tadpole which then undergoes metamorphosis to develop into a frog.  

But why is this step necessary? Couldn’t the tadpole have “learned” to reproduce, not needing the frog anymore? Or why don’t more frogs directly develop from eggs, foregoing the tadpole? – Ergo, what’s the evolutionary advantage of having both?

Charles Darwin was already puzzled by this question, looking at insect larvae and adult insects who likewise undergo metamorphosis. Since they are part of the same life form, he assumed that evolution in one phase surely must be mirrored by the other. But, since there are also such striking differences between a larva and an adult after metamorphosis, maybe evolution affects both phases differently, driving them apart? From this standpoint, one might invoke Goethe’s Faust, reciting: “Two souls, alas, are dwelling in my breast /And one is striving to forsake its brother”.

To decide between these “Darwinian” and “Faustian” viewpoints, an international team of researchers led by the University of Hull and Technical University of Braunschweig studied and compared frog and tadpole evolution of the model frog Xenopus, and the Madagascan mantellid frogs who encompass over 400 species descending from a common ancestor. In the study published in Nature Communications on May 15th, they found that the evolution of tadpoles is entirely independent from the evolution of frogs, despite that they merely represent two phases of the same organism — Faust: 1, Darwin: 0.

“Tadpoles and frogs evolving independently from one another is the explanation for the presence of two such strikingly different phases in the first place”, says Katharina Wollenberg Valero from the University of Hull. “Having different genetic programs responsible for generating adult and tadpole forms may allow each phase to adapt to changes in their environment independently, bypassing possible ill consequences for the other phase”.


Wollenberg Valero, K. C., J. Garcia-Porta. A. Rodriguez, M. M. Arias Villarraga, A. Shah., R. D. Randrianiaina, J. L. Brown, F. Glaw, F. Amat, S. Kunzel, R. D. Isokpehi, D. Metzler, and M. Vences. Phenotypic evolution is uncoupled among frog life history phases. Nature Communications, DOI:10.1038/NCOMMS15213.

Contact and inquiries:

Katharina Wollenberg Valero:

Miguel Vences: