This month’s Current Biology has a “Quick Guide” segment by Brian Hall on atavisms: the occasional and random appearance of ancestral traits in individuals of species that no longer have that trait. Examples Hall provides are vestigial hindlimbs (legs or fins) occasionally found on dolphins or snakes, which evolved from animals that did have limbs.
This is wild, because it implies that part of the ancestor’s developmental program has been furtively retained in its descendants, but this program generally never gets carried out. But every now and again a mutation may arise that causes the ancestor’s developmental program come alive all Franken-style. Nuts!
Here’s a crazy hypothetical example: the axolotl is an evolutionary abomination, a salamander in a state of arrested development. It’s basically a salamander that terminates development in what would otherwise be the larval stage of any other salamander. This is a nice real-life example of heterochrony (changes in the timing and rates of developmental events). Here, it’s a adult descendant that resembles the juvenile form of the ancestor (“neoteny”). (photo credit: John Clare, axolotl.org)
Wouldn’t it be wild, then, if the there was an axolotl in whom the ancestral full-salamander developmental plan was completed, resulting in an accidental salamander?! And then you could try to select for this atavism, possibly breeding peramorphic-atavistic-salamander axolotls (“salamander axolotls” for short)! If grad school doesn’t work out, this’ll be my Plan B.
Poll: If you could have any atavism, what would it be?
Hall BK. 2010. Quick guide: Atavisms. Current Biology 20: R871.