# Flatfish and evolution **URL:** \ **Category:** Factual Questions\ **Created:** [November 21, 2012, 2:58pm UTC](https://boards.straightdope.com/t/flatfish-and-evolution/641720 "2012-11-21T14:58:28Z")\ **Posts on this page:** 6\ **Page:** 2
**Author:** ![RaftPeople](https://avatars.discourse-cdn.com/v4/letter/r/6f9a4e/32.png) [@RaftPeople](https://boards.straightdope.com/u/RaftPeople)\ **Post date:** [November 21, 2012, 6:25pm UTC](https://boards.straightdope.com/t/flatfish-and-evolution/641720/21 "2012-11-21T18:25:56Z")
**Darwin’s Finch** , would you be willing to look at the points in my post and tell me if I’m assuming too much here. Basically it seems to me like a one-shot change of that magnitude would be highly unlikely, but I’m confused by **njtt’s** post implying that it is more likely than a gradual change. Note: I understand you already said gradual in this case, I’m really asking about the chances of a large change like that in one-shot/short time period. ---
**Author:** ![Darwins\_Finch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darwins_finch/32/20304_2.png) [@Darwins\_Finch](https://boards.straightdope.com/u/Darwins_Finch)\ **Post date:** [November 21, 2012, 6:51pm UTC](https://boards.straightdope.com/t/flatfish-and-evolution/641720/22 "2012-11-21T18:51:18Z")
I think that **njtt** is saying that all evolutionary changes, even seemingly large ones, are not _necessarily_ gradual. Which I agree with (though not necessarily with his supposition that “single feature” changes are more likely to be sudden; it would depend greatly on what the feature is and how complex the underlying development for that feature is). Gradualism is a good default position to start from, but it’s not out of the question for seemingly small changes during development to result in profund phenotypic changes in an adult form. I agree with your points in general, while pointing out that they don’t rule out a statistical outlier; e.g., a rapid change, that, while certainly not the norm in evolutionary history, can still occassionally produce significant morphological changes. I think in the specific case of flatfishes, the fossil record provides sufficient evidence that the change was gradual. Were such record absent for them, **njtt** ’s statements couldn’t be ruled out altogether, even if rapid change is not the statistical norm in evolution (for varying definitions of “rapid”…). Of course, such a presumed rapid change would still require evidence. ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [November 21, 2012, 6:52pm UTC](https://boards.straightdope.com/t/flatfish-and-evolution/641720/23 "2012-11-21T18:52:31Z")
But, an eye doing nothing exposed to the hazards of the sea floor is more of a risk - infections, attack of the crayfish, whatever. (“You’ll poke your eye out”). Also, a second eye is backup even if the fish does not do stereoscopic visual interpretation. I think Dracoi has it best. Originally the fish were normal but would lay flat sometimes, then more often, then finally all the time. As it did this, the eye position that better protected the eye and allowed it to be used was more of a survival trait. It’s self-reinforcing. The fish that are safer lying flat and still able to watch for danger the best are most likely to survive. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [November 21, 2012, 7:06pm UTC](https://boards.straightdope.com/t/flatfish-and-evolution/641720/24 "2012-11-21T19:06:50Z")
> [@Darwins\_Finch](#): > > First, the “lower” eye migrates to the “top” of the head as a consequence of skull reshaping during development in extant flatfishes. The larval forms start off symmetrical, and the asymmetry arises during development. This is the part that’s significant. The changes to the head and skull could have been the primary adaptations with the eye following simply based on constraints. ---
**Author:** ![HoneyBadgerDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/honeybadgerdc/32/1033_2.png) [@HoneyBadgerDC](https://boards.straightdope.com/u/HoneyBadgerDC)\ **Post date:** [November 21, 2012, 7:44pm UTC](https://boards.straightdope.com/t/flatfish-and-evolution/641720/25 "2012-11-21T19:44:31Z")
I would suspect with the flatfish that a shortage of food occured. Fish that had the predisposition to swim sideways along the bottom were more successful at catching bottom dwelling crustaceans, the same fish with this predisposition may have also carried recessive genes that could begain development on flatfish. ---
**Author:** ![typoink](https://avatars.discourse-cdn.com/v4/letter/t/ecb155/32.png) [@typoink](https://boards.straightdope.com/u/typoink)\ **Post date:** [November 22, 2012, 1:20am UTC](https://boards.straightdope.com/t/flatfish-and-evolution/641720/26 "2012-11-22T01:20:11Z")
A possible advantage of moving the eye upward could also have been moving it away from debris – evolution doesn’t just select advantages, it also discourages disadvantages. [Previous page](https://boards.straightdope.com/t/flatfish-and-evolution/641720.md?page=1)