Amphistium and Heteronectes
From RationalWiki
Amphistium and Heteronectes were two genera of fish representing the transition toward modern flatfishes, which in their adult form have two eyes on the same side of the head. Flatfish when hatched are symmetrical, but during their growth to maturity one of the eyes migrates to the other side of the head.
Typical modern flatfish lie (in wait for prey) on one side, and have their two eyes on the same side of their head (rather than having them symmetrically located as is typical for vertebrates, which would have one eye uselessly facing downward). The fossils of Amphistium and Heteronectes show a transitional state, with one eye in an intermediate position, moved near the top of the head. This is intermediate between the typical location for eyes in vertebrates symmetrically placed in the head, and the typical location for eyes in flatfishes on the same side of the head. Alternative explanations for this are excluded. For example, there are several fossils of Amphistium known from different locations, so it is not just an isolated malformed fish.[1]
[edit] The challenge to evolution
The evolution of this asymmetry in the positioning of the eyes is a long-outstanding problem for gradual evolution. St. George Jackson Mivart wrote in 1871 (that is, twelve years after the publication of On the Origin of Species):
"Such sudden changes, however, are not those favoured by the Darwinian theory, and indeed the accidental occurrence of such a spontaneous transformation is hardly conceivable. ... It seems, even, that such an incipient transformation must rather have been injurious."[2]
The discovery of these fossils demonstrates that, no matter how inconceivable the transformation was, it did happen; and that the incipient transformation was not so injurious as to preclude the existence of fish in such a state. One of the fossils is of a fish that was successful enough as a predator to have eaten another fish. This discovery shows that the argument from implausibility, as applied by Mivart, is unreliable.
Fossil evidence of two missing links in the evolution of flatfish has now been found. [3]
[edit] Footnotes
- ↑ Matt Friedman, "The evolutionary origin of flatfish assymetry", Nature volume 454 number 7201 (10 July 2008) pages 209-212 doi: 10.1038/nature07108
- ↑ Chapter ii, pages 37, 38 in St. George Jackson Mivart, On the Genesis of Species, London: Macmillan and Co., 1871. [1] http://www.gutenberg.org/files/20818/20818-h/20818-h.htm
- ↑ New Scientist - flatfish caught evolving
[edit] External references
- http://blogs.discovermagazine.com/loom/2008/07/09/dawn-of-the-picasso-fish/ Dawn of the Picasso Fish, Carl Zimmer's blog "The Loom" entry for 2008 July 9
- http://www.sciencenews.org/view/generic/id/33976/title/A_wandering_eye Ashley Yeager, "A Wandering Eye", Science News. Includes a video that "shows the skeletal changes that a flatfish goes through as it develops into an adult fish."
- http://news.nationalgeographic.com/news/2008/07/080709-evolution-fish.html Anne Minard,"Odd Fish Find Contradicts Intelligent-Design Argument", National Geographic News.
