New Structure Evolved in Just 36 Years!

Italian Wall Lizard, Podarcis sicula

Rapid large-scale evolutionary divergence in morphology and performance associated with exploitation of a different dietary resource | PNAS

It's another one of those 'non-existent' things that creationists must dread being shown.

No. This time it's not yet another of those 'missing' transitional fossils or intermediate forms. This time it's yet another example of something else 'impossible' and 'never observed'. It's yet another example of observed rapid evolution, including the evolution of new structures.

It's a paper from 2008 that utterly destroys a key creationist claim, yet they are still making it. Thanks to @GrrlScientist for promoting this research today.

To begin at the beginning.

In 1971 a bunch of scientists, intending to observe how a population of the Italian wall lizard, Podarcis sicula, adapted to a new environment, transferred just five males and five females from the small Croatian island of Pod Kopiste in the southern Adriatic Sea, to the nearby island of Pod Mrcaru. And there they stayed while Yugoslavia fragmented and descended into warring factions.

Thirty-six years later another group of scientists visited the island, where they discovered that not only had the teeming descendants of the relocated lizards replaced and apparently exterminated the former resident species, Podarcis melisellensis, on Pod Mrcaru, but that they had also diverged considerably from the original population on Pod Kopiste. That they were indeed the descendants of the original founder population was confirmed by analysis of their mitochondrial DNA, which was identical to those on Pod Kopiste.

Their findings were published in 2008 in PNAS.

The major significant changes were:

• A change of diet. The Pod Mrcaru lizards now eat mostly plant material, not the insects their ancestors ate.
• To cope with this different diet, the Pod Mrcaru lizards have a measurably larger head which allows for more powerful jaw muscles and a more powerful bite, needed to bite the plant matter into small chunks for swallowing and digestion.
• The Pod Mrcaru lizards are less territorial and less aggressive than their ancestors because they no longer need to defend a territory to ensure enough insects. This has enabled a much higher population density. They are also less active.
• To digest the vegetarian diet, the Pod Mrcaru lizards have developed caecal valves in their intestines. These slow down the flow of food through the digestive system and act to turn sections into fermentation vats to break down the plant cell walls.

This latter is the most dramatic morphological change since only 1% of lizard species have caecal valves. It amounts to a new structure in this species, evolved in just 36 years.

Here then we have a measurable morphological, behavioural and ecological changes in a population in just 36 years and the evolution of new structures in the gut, all brought about by a change in the environment.

Unfortunately for creationists, the usual response to this sort of evidence of observed evolution is to fall back on an artificial distinction between what they call 'macro-evolution' and normal evolution and proclaim it to be 'still lizard kind' as though under this definition of 'kind', all lizards are the same 'kind'. However, when pressed to explain what 'macro-evolution' is, they will normally include different structures.

So what they need to explain in this example is why evolving a new structure is not a change in kind. Any creationists prepared to try for a new definition of evolution which includes the evolution of a new structure while still being the same 'kind'?

Reference:

Herrel, A., Huyghe, K., Vanhooydonck, B., Backeljau, T., Breugelmans, K., Grbac, I., Van Damme, R., Irschick, D.J. (2008).
Rapid large-scale evolutionary divergence in morphology and performance associated with exploitation of a different dietary resource.
Proceedings of the National Academy of Sciences, 105(12), 4792–4795. DOI: 10.1073/pnas.0711998105

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