"Whether fish or flies - at a certain stage in their development, the embryos of different animal species within a phylum are almost impossible to distinguish on the basis of their appearance. The greatest similarity arises in the middle of embryonic development, during the "phylotypic stage"; species-specific differences predominate before and after this stage. This observation is illustrated by the hourglass model. The question as to how this extensive morphological similarity - the "waist" of the hourglass - arises is one that has long preoccupied researchers. The extent to which the individual development of an organism (ontogeny) and that of a phylum (phylogeny) are linked was also previously unclear. Scientists have now demonstrated that the hourglass motif arises in organisms as diverse as the fruit fly and zebrafish, not only at morphological level but also at molecular level - a finding that suggests that parallels do, indeed, exist between #ontogeny and #phylogeny." Read at bit.ly/14TbOF7 More accurate pictures, that reflect better the scientific evidence: millerandlevine/km/evol/embryos/Haeckel.html (Thanks to Emil Karlsson for the link) #Evolution #embryology Image source: Ontogeny Images: fotosimagenes.org/ontogenia
Posted on: Mon, 15 Jul 2013 07:11:49 +0000
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