The "Hulk" lizard.
Photo: Roberto García Roa.
This lovely example of evolution in progress will no doubt have creationists demanding that science abandon its definition of evolution and adopt their childish “change of kind” parody instead — a caricature which, if it meant one basic type of organism suddenly turning into another, would falsify evolution rather than confirm it.
The example concerns the common wall lizard, Podarcis muralis, a species widespread in the Mediterranean region. For millions of years, populations of this lizard have included three genetically determined throat-colour morphs: white, yellow and orange. These colour forms are not merely superficial differences. They are associated with different strategies for gaining territories, attracting mates and competing with rivals, and their long-term coexistence has been a textbook example of evolutionary balance maintained by natural and social selection.
Now that balance has been disrupted by the spread of a new phenotype: a larger, bright green, aggressive and sexually dominant form, known to science as the green-and-black, white-throated nigriventris phenotype, nicknamed the “Hulk” by the researchers appears to have arisen near Rome several thousand years ago (a mere tick in evolutionary time) and is now spreading through Italy.
As this form spreads through the landscape, the yellow- and orange-throated morphs are disappearing, leaving the white-throated form behind. The change has been so rapid that, had it involved a marked alteration in a structure likely to fossilise, such as teeth or bones, it would appear in the fossil record of the future as a sudden change after a long period of stasis — in other words, exactly the kind of pattern described by punctuated equilibrium. It is, of course, classic evolution: allele frequencies in populations shifting as a newly successful phenotype spreads.
This evolutionary change in progress is the subject of a paper in Science by an international team of researchers led by Professor Tobias Uller of Lund University, Sweden. The team analysed colour data from about 240 populations of P. muralis, comprising more than 10,000 individuals. The results show that the newcomer has significantly altered the long-standing balance within the species, eliminating the yellow and orange morphs as the larger, more aggressive form spreads through the region.
Colour Morphs, Sexual Selection and Evolution in Action. A colour morph is a distinct, inherited colour form within a species. In the common wall lizard, Podarcis muralis, males occur in different throat-colour forms, including white, yellow and orange. These colours are not merely decorative. In many animals, such morphs are associated with different behaviours, mating strategies, territorial behaviour or physiological differences, so natural and sexual selection can act on them indirectly through the advantages or disadvantages linked to each form.
For millions of years, the white, yellow and orange morphs of the common wall lizard appear to have coexisted in a stable evolutionary balance. No single form permanently eliminated the others because each persisted within the shifting mixture of competition, mating success and local conditions. This is known as a balanced polymorphism — a situation in which more than one inherited form is maintained in a population.
The newly spreading “Hulk” phenotype shows how quickly such a balance can be disrupted. Larger, green, aggressive and sexually dominant, it is spreading through Italy and is associated with the disappearance of the yellow and orange forms, leaving populations increasingly dominated by the white-throated form. This is evolution in its proper scientific sense: heritable variation being sorted by selection, causing the genetic and visible composition of populations to change over time.
Nothing has changed “kind”. No lizard has stopped being a lizard. But the population is evolving all the same — which is precisely why the creationist parody of evolution is so useless. Evolution is not magic transformation; it is the change in inherited traits in populations, and here it is happening in plain sight.
Sadly, the paper in Science is behind an expensive paywall, but we have an account of the research and its significance in a Lund University news article by Johan Joelsson:
“Hulk lizard” knocks out ancient colour palette
A myriad of colours that survived millions of years of evolution have disappeared in a short period of time. The culprit? A bright green, aggressive, and sexually dominant wall lizard that has wiped out several colour variants within its species.
Many animal species display clearly defined colour variants, or colour morphs. These are not just superficial differences, but are often linked to different strategies for securing access to territories, mates, or similar advantages.
The common wall lizard (Podarcis muralis) is a species widespread in the Mediterranean region, and can have three different throat colours: white, yellow, and orange. These have coexisted within the same populations for millions of years and served as a textbook example of stable evolutionary balance. However, in a new study published in Science, a research team led from Lund University shows that this balance has now been broken.
We are seeing how the coexistence of several different colour morphs, something that has been stable for millions of years, is being lost over a very short evolutionary time scale.
Professor Tobias Uller, lead author.
Department of Biology
Lund University
Lund, Sweden.
Data from over 10,000 lizards
As the "Hulk" lizards spread across the landscape, the yellow and orange throat colours also disappear.Photo: Roberto García Roa.
The researchers analysed colour data from about 240 populations of wall lizards, totaling more than 10,000 individuals. The results speak for themselves. The so‑called Hulk lizards - large, aggressive lizards with a characteristic appearance - have shifted the balance within the species.
As the "Hulk" lizards spread across the landscape, the yellow and orange throat colours also disappear. Only the white colour remains.
The aggressive behaviour disrupts the finely tuned social systems that previously enabled several colour strategies to coexist.
Professor Tobias Uller.
Evolution not always slow
The colour study is unique. It shows how long‑lasting sets of colours within a species can be surprisingly vulnerable. Evolution is not always slow and balanced - sometimes a single new, powerful player is enough to rewrite the rules.
By showing how colour variants that have coexisted for millions of years are wiped out, we now better understand how the emergence of new traits changes competition in nature.
Professor Tobias Uller.
Publication:
The lesson for creationists is as awkward as it is simple: this is evolution in action, exactly as science defines it. A heritable variation has appeared, spread through populations, altered the balance of existing forms, and changed the frequency of traits within the species. No lizard has had to turn into a crocodile, bird or mammal. No imaginary “change of kind” is required, because that was never what evolutionary biology predicted in the first place.
Creationists, of course, will try to dismiss this by claiming it is “only variation within a kind”, as though repeating a slogan can make the evidence go away. But variation within populations, filtered by natural and sexual selection over generations, is precisely the raw material of evolution. It is how populations adapt, diverge and, given enough time and isolation, can eventually give rise to new species. Demanding “evolution in action” and then rejecting it when it is shown happening is not a scientific objection; it is moving the goalposts.
The common wall lizard has provided a particularly neat example because the change is visible, measurable and occurring across real populations in real landscapes. The ancient balance between colour morphs has been disrupted by a more successful phenotype, and the population is being reshaped accordingly. If such a rapid shift affected bones or teeth, future fossil hunters might see it as sudden change after long stability — the very pattern creationists so often misrepresent as a problem for evolution.
So here, once again, the evidence does what evidence always does: it supports the scientific model and ignores the theological special pleading. Evolution is not a cartoon in which one “kind” gives birth to another. It is the cumulative sorting of heritable variation by real-world conditions. In these Italian wall lizards, that process is not hidden in theory or buried in fossils. It is happening now, in living colour.
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