Contributions to Zoology, 86 (4) – 2017Jacques J. M. van Alphen; Jan W. Arntzen: The case of the midwife toad revisited
Unexplainable aspects in Kammerer’s experiments

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Mating behaviour and nuptial pads

It is hard to understand how the experiment described in the Kammerer (1919) paper could have resulted in F1 water-breeding offspring without parental care, irrespective of the temperature regime applied. Selection in one generation cannot have resulted in the disappearance of the normal breeding behaviour, and the animals continuously kept at lower temperatures after exposure to the experimental temperatures might be expected to have resumed the original land-breeding behaviour.

According to Kammerer, water-breeding males developed nuptial pads, but these did not appear until the third generation. At that stage of Lamarckian evolution, the pads were scarcely visible and only they became fully expressed in the fifth generation. An epigenetic explanation of the appearance of the nuptial pads must also explain why the expression of this character increases gradually over the generations. If Kammerer really produced male midwife toads with nuptial pads in his experiments, the most likely explanation is that he had used a wild-caught male with nuptial pads (as are rarely found in nature, see Kändler, 1924) and, with this very male, raised offspring also in possession of nuptial pads.