Does ontogeny recapitulate phylogeny? Is there embryonic evidence that our early development is repeated? The?

Question

common answer given is that there are signs of gill sllits on the necks of embroyos in the early stages. Implying that humans came from the sea. But are they really gill slits or formations that turn into other features. I bet that many of you lie away at night pondering this.

Answer 1

They are not really gill slits insofar as allowing the fetus to breath while floating inside the amniotic fluid. The umbilical cord provides all of the nutrients and oxygen that the fetus requires to survive. They do suggest a relation to earlier life forms. How closely the relationship is to earlier life forms requires close study of the anatomy at that stage of development and comparing it to specimens of those creatures.

The theory of recapitulation, also called the biogenetic law or ontogeny recapitulates phylogeny, is a theory in biology which attempts to explain apparent similarities between humans and other animals. First espoused in 1866 by German zoologist Ernst Haeckel, a contemporary of Charles Darwin, the theory has been discredited in its absolute form, although recognized as being partly accurate. In biology, ontogeny is the embryonal development process of a certain species, and phylogeny a species' evolutionary history. Observers have noted various connections between phylogeny and ontogeny, explained them with evolutionary theory and taken them as supporting evidence for that theory.

Modern theory
One can explain connections between phylogeny and ontogeny if one assumes that one species changes into another by a sequence of small modifications to its developmental program (specified by the genome). Modifications that affect early steps of this program will usually require modifications in all later steps and are therefore less likely to succeed. Most of the successful changes will thus affect the latest stages of the program, and the program will retain the earlier steps. Occasionally however, a modification of an earlier step in the program does succeed: for this reason a strict correspondence between ontogeny and phylogeny, as expressed in Ernst Haeckel's discredited recapitulation law, fails.

Answer 2

Raymond wrote it simultaneosly and better than me: they ARE actual gill slits homologues, but do not function as breathing apparatus of the foetus!!! that would be a huge misconception - they function only as a reminder of the fish stage , nothing more. . The recapitulation works only to some degree , and not that we would actuallx TURN INTO FISH, REPTILES ETC IN SUCCESSION...:)

when i lie at night i ponder why it is so horribly hot these days actually

tonight maybe i will try to remember - unsuccessfully - the bio lessons on what the individual gill pairs eventually develop into in mammals, i can remember that this was quite difficult to study and to remember correctly as they are some 7 pairs of them and me being a botany student i happily forgot it all soon after the zoology exam at college was over. and also i was happy that the teacher did not ask me this at the exam....some 12 years ago. at THAT time it gave me sleepless nights together with Ascidium life cycle, that one was even worse..

Answer 3

nope, that theory it's out of market... this theory standed that every stage in development of an embryo was an organism that had existed... Now it's proved that the development of an embryo (no matter what organism is) it's very similar because we all have a common ancestor, that's why a chicken or a human or a pig when they are 1 month old you can't practically distinguish one another. HOX genes are the responsibles of the early development of organisms, the most evolved the most HOX genes are expresed, these HOX genes express in the very first stages of development.

Answer 4

Well, I'll be a monkey's Uncle.
If I pondered this all night I might be afraid that the next time I bought a "Filet-O-Fish" at Rotten Ronnie's I may be munching on my Uncle Tony.

Answer 5

...no, i never have... when i took developmental bio, the slits eventually closed and the tails were reabsorbed. not rocket science, bob!