A tree frog shown before and after the
Chernobyl nuclear accident in 1986
I.
I have always liked D. H. Lawrence's description of little green frogs as gem-like [1].
But it seems that the frogs living in the Chernobyl Exclusion Zone (CEZ) are no longer emerald green in colour. For in order to increase their survival rates in an irradiated environment, the frogs have undergone rapid evolution and now model jet black skins rich in protective melanin [2].
In 2016, whilst researching the effects over the previous three decades of Chernobyl's uniquely polluted environment on the
flora and fauna, two Spanish scientists [3] made a strange discovery ...
They expected to find that plant and animal species subjected to daily doses of radiation way above normal levels would have experienced negative consequences, but what they did not anticipate was that nature would respond in such an amazing way and recover so quickly - and they certainly weren't on the lookout for black frogs!
II.
So, what on earth is going on here?
Well, cancer resistant wolves [4] and ebony-skinned tree frogs would seem to suggest that the Chernobyl disaster, which generated the largest release of radioactive material into the environment in human history, has accelerated natural evolution in a manner that Darwin - who always liked to stress the slow and gradual nature of evolutionary change by natural selection [5] - would have found hard to believe.
And this - along with the absence of human beings - helps to explain why Chernobyl has become one of the largest nature reserves in Europe, where a diverse range of endangered species find refuge and live happily (or at least successfully) side-by-side.
For whilst acute exposure to high doses of radiation can cerainly be damaging, both to the natural environment and the genetic material of living organisms, it can also kick-start and accelerate evolution in a surprisingly positive way, as species adapt to the new conditions.
Notes
[1] See D. H. Lawrence, 'The State of Funk', in Late Essays and Articles, ed. James T. Boulton, (Cambridge University Press, 2004), p. 221.
[2] The pigment melanin which, as many people know, reduces the effects of ultraviolet radiation, can also, so it seems, afford protection against ionising radiation. And that's why it's better to be a black frog than a green frog if you're going to spend your life hopping about in the CEZ.
[3] Germán Orizaola and Pablo Burraco; they discuss their study of over 200 male tree frogs taken from twelve different breeding ponds from various sites in northern Ukraine - including four outside the CEZ - in an article originally published on theconversation.com (28 Sept 2022): click here.
As Orizaola y Burraco make clear, the dark skin colouration is typical of
frogs from within or near the most contaminated areas at the time of the
Chernobyl disaster and it suggests that they have undergone a process of rapid evolution in response to the radiation. The black frogs, having better survival rates, are now the dominant type within the CEZ, which, in my view, is a bit of a shame, as I prefer the little frogs with bright green skins.
[4] See the recent post entitled 'Cara Love and the Mutant Wolves of Chernobyl' (14 Feb 2024): click here.
[5] In what is considered to be the founding text of evolutionary biology - On the Origin of Species (1859) - Darwin emphasises how natural selection progresses at a glacial pace and we usually observe nothing of the changes being made until long periods of time have passed.
Although this is true, adaptation to new conditions can occur within a relatively short period of time and examination of the fossil record shows that many species undergo rapid bursts of evolution, even if true speciation takes time. Recent work in developmental biology has identified certain mechanisms of tissue morphogenesis that may help explain any swift structural transitions.
I am grateful to Dr Andy Greenfield - my go to science guy and longtime friend - for his guidance on this point.
For a frog-related follow-up post to this one, click here.
