Darwin can rest in peace
The asymmetry of the skull of flatfish is the result of a progressive adaptation of the species. A study in Nature
The bizarre anatomy of flatfish had surprised even Charles Darwin, which had not managed to find an explanation for the asymmetry of their skull. All adult in this family - including the sole, turbot, halibut - in fact, have both eyes on the top of the head. But in fossils of fish of their progenitors, this feature was absent. The mystery of the asimmetric skull is now being revealed by a study carried out by Matt Friedman, a researcher at the Committee on Evolutionary Biology and the University of Chicago and State Department of Geology at the Field Museum and published in Nature: in the Eocene era, about 50 million years ago, there were fish with intermediate characteristics.
The U.S. researcher says it is enough to review the collections of fossils preserved in museums in some European countries (Italy, France, Austria, United Kingdom) to be able to find two kinds primitive - Amphistium, described for the first time more than 200 years ago, and the Heteronectes, unknown until now - in which the eye migration is partial. "We discovered thus an intermediate stage of development of these species," said Friedman, "showing that the asymmetry of the head of the fish we know today is the result of a gradual natural evolution."
The bizarre anatomy of flatfish had surprised even Charles Darwin, which had not managed to find an explanation for the asymmetry of their skull. All adult in this family - including the sole, turbot, halibut - in fact, have both eyes on the top of the head. But in fossils of fish of their progenitors, this feature was absent. The mystery of the asimmetric skull is now being revealed by a study carried out by Matt Friedman, a researcher at the Committee on Evolutionary Biology and the University of Chicago and State Department of Geology at the Field Museum and published in Nature: in the Eocene era, about 50 million years ago, there were fish with intermediate characteristics.
The U.S. researcher says it is enough to review the collections of fossils preserved in museums in some European countries (Italy, France, Austria, United Kingdom) to be able to find two kinds primitive - Amphistium, described for the first time more than 200 years ago, and the Heteronectes, unknown until now - in which the eye migration is partial. "We discovered thus an intermediate stage of development of these species," said Friedman, "showing that the asymmetry of the head of the fish we know today is the result of a gradual natural evolution."
The asymmetry is an advantage for these fish, given that they move along the seabed. If their eyes were positioned differently, in fact, could not enjoy binocular vision. This characteristic is also the result of the development of fish: in early life, the symmetry is still respected, then during the ripening process an eye "migrates" towards the top of the skull, reaching the position when the fish is now adult.
This is a discovery that opponents of evolutionism should be evaluating carefully. According to critics of Darwin, in fact, the lack of "intermediate" specimens showed that there was an advantage for fish with a skull only partially asymmetrical and therefore the peculiar anatomy of fish could not be a natural selection.
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