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Ernst Haeckel and the "Stage phylotypes"

As promised and after a long absence (I was at a conference of Developmental Biology in Santa Cruz, Chile), today talk of Ernst Haeckel, a German biologist who made a remarkable observation. He observed that no matter what kind you are, the early embryos are all more or less the same! I leave a drawing by the famous, try not to read the names below and see the first row of embryos, guess which species corresponds to each, if you go down each column represents time in development:

The answer is as follows, from left to right: Fish, salamanders, turtles, chicken, pork, veal, rabbit and of course, a human being (again we realize that we are not as exclusive.) This is what Haeckel postulated as the "recapitulation theory" claiming that "ontogeny recapitulates phylogeny," but what does that mean?, We must define the terms:

• Ontogeny: This is the development of an organism , since it is an egg until it becomes an adult, is the definition of "philosophical" in the subject matter of developmental biology
Phylogeny
• This is a more familiar term that describes the evolutionary relationships between species in this planet.

So what Haeckel wanted to say very elegant, is that the development of an organism may be a reflection of their evolutionary history in a more or less linear (that is currently not accepted in their literal form, not is that the development go through fish, reptiles, mammals, etc ...). Therefore, the more closely related are two species, but its development is similar. On the other hand, the early stages of development of animals of a given group are all basically the same due to the phenomenon of common descent. That is why if one observed in early embryos of vertebrates formalin bottles are not labeled, believe me it will cost a world guess what the human and what is the rabbit or dog.
is this stage of development where all the animals of an edge we are equal, which was called "Stage phylotypes. Recall that we belong to the edge of the chordates, so when we are embryos, we have nothing to envy to the whales, dogs, tigers and turtles.