phylotypic

One idea is that these “whole body” specification events are conserved and are difficult to uncouple from one another, so all the features for which they are responsible tend to appear together in a coordinated fashion…and that coordination is what we call the phylotypic period.

The Politically Incorrect Guide to Darwinism and Intelligent Design Review: Simply Incorrect Embryology (Chapter 3) - The Panda's Thumb 2006

All of Wells 'indignation is a smokescreen, intended to cover up an uncomfortable point: namely, vertebrate embryos do pass through a stage, called the phylotypic stage or the pharyngula, in which they all look very similar.

Planet Atheism 2009

What it illustrates is that we have great diversity in the earliest stages of development, in the blastula and gastrula and neurula, but that they all converge on a more similar form, the pharyngula, at what’s called the phylotypic stage…and then they diverge once again to achieve the diversity of adult forms.

The Politically Incorrect Guide to Darwinism and Intelligent Design Review: Simply Incorrect Embryology (Chapter 3) - The Panda's Thumb 2006

Wells makes much of the fact that the biogenetic law presumes that embryos ought to be most similar at the earliest possible stage of development, yet the period of greatest similarity, the phylotypic stage, occurs well into development, and that the earliest stages exhibit seemingly significant differences.

A bit more on Haeckel - The Panda's Thumb 2010

The phylotypic stage, when the Hox genes are exhibiting their standard patterns of expression, of humans is at 4-5 weeks out of 40 weeks, and in zebrafish it's at 18-24 hours.

Jonathan Wells gets everything wrong, again - The Panda's Thumb 2009

The pharyngula stage/phylotypic stage is the time when Hox gene expression is ordered and active, when organogenesis is ongoing, and when the hallmarks of chordate embryology, like segmental myotomes, a tailbud, and branchial arches are forming.

Jonathan Wells gets everything wrong, again - The Panda's Thumb 2009

For instance, somites, one of the body elements characteristic of the phylotypic stage, form under the influence of a somitic clock, rhythmic waves of molecular activity that sweep the length of the trunk and tail.

The Politically Incorrect Guide to Darwinism and Intelligent Design Review: Simply Incorrect Embryology (Chapter 3) - The Panda's Thumb 2006

What is it that shelters the phylotypic stage to some degree as yet unquantified from the evolutionary divergence so common in other developmental processes?

The Politically Incorrect Guide to Darwinism and Intelligent Design Review: Simply Incorrect Embryology (Chapter 3) - The Panda's Thumb 2006

One serious question is about how wide the waist of the hourglass actually is: an overzealous Haeckelian interpretation would be that it is very narrow indeed, but serious embryology none of which seems to be done by “intelligent design” proponents demonstrates that there is a significant amount of variation within the phylotypic period.

The Politically Incorrect Guide to Darwinism and Intelligent Design Review: Simply Incorrect Embryology (Chapter 3) - The Panda's Thumb 2006

PZ himself acknowledges this stating, serious embryology none of which seems to be done by “intelligent design” proponents demonstrates that there is a significant amount of variation within the phylotypic period.

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