Darwin’s theory of biological evolution noted that all vertebrates have gill slits and tails in early stages of embryo formation, even though these features may be lost or modified in … For example, all vertebrate embryos have "gill slits" which are not actually gills. Example: All vertebrates embryos have gill slits, which may become gills or ear bones. D. Biogenesis. A. Recapitulation. Mayr is not claiming that human embryos actually have the gill slits of a fish. Many traits of one type of animal appear in the embryo of another type of animal. The vertebrae and nervous systems develop early so all embryos appear to have a tail. More recently, embryologists … It becomes very difficult to differentiate between the embryos of a fish, and that of a bird, or embryo of a fish, and a human. Animals in the phylum Chordata share four key features that appear at some stage during their development: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and; a post-anal tail. B. Organic evolution. German zoologist Ernst Haeckel is perhaps most famous for defending evolution with the argument that creatures replay their evolutionary past when developing in the womb. As chordates, all vertebrates have a similar anatomy and morphology with the same qualifying characteristics: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail. All vertebrate embryos follow a common developmental path due to their common ancestry. The most conspicuous and familiar members of Chordata are vertebrates, but not all have vertebrae. Both fish and bird embryos exhibit gill slits and a tail. All vertebrate embryos follow a common developmental plan due to having a set of genes that gives the same instructions for development. Explanation: According to embryology, all vertebrates exhibit similar traits and structures at their embryonic stage. So what makes a chordate, a chordate? The presence of gill slits in the embryos of all vertebrates supports the theory of. The theory of recapitulation, also called the biogenetic law or embryological parallelism is often expressed in Ernst Haeckel's phrase as "ontogeny recapitulates phylogeny". Like all chordates, vertebrates have a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail. According to the recapitulation theory, early human embryos have structures like gill slits, so, therefore, early human embryos represent the form of adult fish, which also have gill slits. They connect the throat to the outside early in development but eventually close in many species; only in fish and larval amphibians do they contribute to the development of gills. Embryos of all vertebrates have deep structural similarities and these deep similarities are said to clearly show evidence for evolutionary relationships. look very similar and it is often difficult to tell them apart. The nerve cord, notochord, postnatal tail, and pharyngeal slits are the four characteristics that are present in the chordates. The embryos of birds and mammals clearly show gill-like structures, more technically called pharyngeal arches. MEDIUM. Embryos of many different kinds of animals: mammals, birds, reptiles, fish, etc. Since Darwin's time, textbooks have reiterated that early embryos of many vertebrates, including humans, have tiny pouches that reflect an evolutionary fish stage. The development of the human embryo reveals steady progress toward a fully functional human body. C. Metamorphosis. For example, fish embryos and human embryos both have gill slits. So, the embryo of all chordates does not have a backbone. The so-called gill slits of a human embryo have nothing to do with gills, and the human embryo does not pass through a fish stage or any other evolutionary stage. 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