Here is a chicken that due to a mutation got 4 legs:

enter image description here

I wonder, are there examples, where such one-time dramatic mutational chages gave rise to a new species?

Are there species that appeared not due to gradual mutations, but something like this?

For instance:

  • A new instance or pair of organs appear, such as an extra pair of limbs.

  • An organ reverts to its function in distant acestors (like wings to legs or legs to fins), using already existing genetic code (e.g, not like in penguins or dolphins, gradually but abruptly).

  • A long-lost organ re-appears (like tail)

  • $\begingroup$ Why do you think this is a "dramatic mutation"? Seems to me like a quite basic, simple one, and possibly not a mutation at all. $\endgroup$
    – Bryan Krause
    May 15 at 13:42
  • $\begingroup$ This chick will most likely not be able to reproduce (having raised chickens and roosters, it doesn't look like fertilization will be possible.) Not reproducing will mean the end of that 'mutation' (agree it's not a genetic mutation.) "Dramatic mutations" have costly consequences and usually die in utero or before reproducing. Re: organ duplication; without surgery, the only survivable one I've encountered was extra kidneys. Polydactyly is fairly common, though. The answer to your question is "No." Finally, a surviving example is not a new species; the chick is still a chick, but with 4 legs. $\endgroup$ May 15 at 14:08
  • $\begingroup$ FYI: polymelia is the name for a congenital disorder resulting in extra limbs. Often (though not always), this is a result of a partially degenerated twin. Your image would not be the first identified case in chickens: in fact, in 2006, many news outlets ran an AP story about an older chicken with this condition [photo here]. $\endgroup$ May 15 at 20:50
  • $\begingroup$ @theforestecologist interestingly, in the both cases the front legs are functional but the back legs are not. $\endgroup$
    – Anixx
    May 15 at 20:56
  • $\begingroup$ @Anixx also, how are you wishing to define "species" here? (i.e.,by which "species concept" are you binning?). E.g , morphological concept may suggest you already have a new species, whereas both an ecological concept and a phylogenetic concept would not... Additionally, "extreme" morphological changes due to a single genre mutation are not that common, especially since such mutations often have deleterious effects. Also, as I mentioned, your specific chicken case is likely due to a failed twin separation and not a mutation, so no opportunity for evolution (allele freq change) has occurred... $\endgroup$ May 16 at 3:52


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