Starspun

True or false? and do you have a link. The yahoo boards are a hot topic atm. a xtian says recapitulation has ben proven false. true?

Starspun

oh, and crap posts like this:

Let me start out by saying that when you read an artical,hear something on the news etc.. and you hear them talking about evolution they make it out as FACT, but it's not!! all they have are guesses(that why scientist call it the "theory of evolution") I don't care if you don't belive in in a higher being, but you belive in Joe Scientist who's being the bigger fool! Yes I belive in God and this brings me great comfort that there is a point to all of this.If you belive all we are is a bunch of animal's or a desent of a monkey then why don't you start acting like what you are an ANIMAL an go live in the jungle with all of the other critter's. This is a shame think about what your life means and what others mean to you.

Oh by the the way for all of you Darwin freaks out there may I remind you that Darwin himself said his theory was flawed later in life.There are many modern scientist who belive that evolution is not factual,it's just that we don't hear much about them because they would be ridiculed and lose respect in the scientific community.They have yet to find any concret evidence linking man to ape (that's why they are looking for the "missing link").

Any scientist wanna come over and have a grnad time with idiocy?

Hallucigenia

To my knowledge, recapitulation has been under fire since, oh, before Darwin wrote Origin. von Baer developed (uh...so to speak) his laws of development back in the 1840s:
1.The general features of a large group of animals appear earlier in the embryo than the special features.
2.Less general characters are developed from the most general.. until finally the most specialized appear (limb buds).
3.Each embryo of a given species, instead of passing through the stages of other animals, departs more and more from them.
4.Fundamentally, therefore, the embryo of a higher animal is never like [the adult of] a lower animal, but only like its embryo.

I'm no expert in embryology, but my understanding is that von Baer's Laws have much more logical force than strict, Haeckelian recapitulation ever did.

From <a href="http://www.ucmp.berkeley.edu/history/haeckel.html" target="_blank">Ernst Haeckel's biography at the UCMP site</a>:
[Fixed formatting in above quote]

[ July 10, 2002: Message edited by: Hallucigenia ]</p>

lpetrich

I like to translate "ontogeny recaptulates phylogeny" into "growth reruns evolution"; Haeckel liked coining fancy words.

There's a limited, hand-waving degree of truth to it, but there are lots of departures from simplistic recapitulationism.

One example is that amniote (reptile, bird, mammal) embryos are relatively stubby, with big, stubby heads, compared to fish and amphibian embryos, which are relatively elongated.

Another example is larval adaptations, many of which are hard to call some ancestral state.

Caterpillars have a variety of color schemes, usually various camouflage colors; some of them are hairy.

Mosquito larvae live in water, suspended head downward from the surface, with a small rearward tube for breathing through.

Some parasitic-wasp larvae have a remarkable adaptation to living inside of a still-living host; they are careful about what parts to eat, first eating fat deposits, digestive system, and other less-essential parts before turning to the more essential parts of their victims, like the heart and central nervous system.

Tadpoles have no external side limbs; these sprout as the tadpole becomes an adult frog.

However, a lot of features are highly conserved, sometimes across phyla. For example, all chordates have, at some time in their lives, a notochord and pharyngeal slits. In vertebrates, the notochord becomes the spinal cord, only "surviving" in the pads between vertebrae. The pharyngeal slits were originally for filter feeding (swallow a lot of water and keep everything that won't fit through those slits), but in fish, they contain gills, and in amniotes, they half-develop and are then turned into other features or are resorbed.

Some similarities go across phyla, as has been revealed by studies of the molecular mechanisms of embryonic development.

The famous Hox genes are present across the bilaterally-symmetric members of the animal kingdom. These are involved in front-to-rear patterning; with each one expressed in some definite zone along the front-to-rear axis. Each one specifies rearward identity; if absent, its area becomes like the next one forward.

Furthermore, these genes always have the same order in the genome, an order that corresponds to their expression-location order.

Likewise similar are genes involved in dorsoventral (back-to-belly) patterning. They are highly conserved, but vertebrates and arthropods have reversed arrangements! This is in agreement with the arrangement of their internal organs, which had prompted Geoffroy St. Hilaire to propose this inversion about 160 years ago.

The gene Pax-6 is widely shared, and it is involved with starting the development of eyes -- eyes that vary widely in architecture. So those eye details had been invented after Pax-6.

The gene "distal-less" is expressed in the development of a variety of limbs -- insect ones, vertebrate ones, starfish tube feet, etc. However, the limbs themselves would be hard to call homologous across phyla, meaning that it's a limb-growth mechanism that 's shared -- complete with "distal-less".