The study of the similarities and differences in the embryos of different species
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Embryo Comparisons
Although Mayr uses Haeckel’s original drawings in his book, he acknowledges that Haeckel’s famous claim that “ontogeny recapitulates phylogeny” is now known not to be true, because as noted above a human embryo does not repeat the adult stage of any previous ancestor. Creationists and supporters of Intelligent Design will also make a big deal out of the fact that the evolutionary biologist Michael K. Richardson has shown that Haeckel’s original drawings were fudged and idealized to fit Haeckel’s more radical theory. Haeckel made similarities appear more similar than they are and he downplayed differences. However, anti-evolutionists ignore that even Richardson has claimed, “Haeckel's much-criticized embryo drawings are important as phylogenetic hypotheses, teaching aids, and evidence for evolution.” “Haeckel's ABC of evolution and development.” Biological Reviews, Cambridge Philosophical Society. 2002 Nov; 77(4):495-528. The embryos of birds and mammals clearly show gill-like structures, more technically called pharyngeal arches. Mayr is not claiming that human embryos actually have the gill slits of a fish. Embryos of all vertebrates have deep structural similarities and these deep similarities are said to clearly show evidence for evolutionary relationships. Recommended textbook solutionsHuman Resource Management15th EditionJohn David Jackson, Patricia Meglich, Robert Mathis, Sean Valentine 249 solutions
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Human Resource Management15th EditionJohn David Jackson, Patricia Meglich, Robert Mathis, Sean Valentine 249 solutions  Molecular Cell Biology6th EditionArnold Berk, Chris A Kaiser, Harvey Lodish 234 solutions If you're seeing this message, it means we're having trouble loading external resources on our website. If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked. The astonishing similarity in the appearance of embryos from different animal species was observed as far back as the 19th century by scientists such as Karl von Baer, Charles Darwin and Ernst Haeckel. Such observations prompted the hypothesis that the individual development of an organism reflects its evolutionary history or phylogeny. Two groups of scientists, including researchers at the Max Planck Institute of Molecular Genetics in Dresden and the Max Planck Institute for Evolutionary Biology in Plön, have now succeeded in demonstrating, for the first time, that parallels exist between individual development and phylogeny on the level of gene expression. The research is published in the journal Nature (Dec. 9, 2010). 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. For the first time, 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. In a study carried out on six fruit fly species (Drosophila sp.), the research group working with Pavel Tomancak at the Max Planck Institute of Molecular Cell Biology and Genetics in Dresden discovered that the similarities not only in morphology, but also in the expression pattern of the genes are greatest during the phylotypic stage; before and after this phase, the differences between the species are greater. Moreover, the scientists also observed that the expression pattern of key genes reflects the hourglass model most faithfully. Meanwhile, Tomislav Domazet-Lošo and Diethard Tautz, researchers at the Max Planck Institute for Evolutionary Biology in Plön, demonstrated with zebrafish (Danio rerio) that the phylogenetically oldest genes are active during the phylotypic stage and that, before and after this stage, the most active genes are those that arose later in evolutionary history. The Plön-based evolutionary biologists also made another astonishing discovery: they observed that in adult zebrafish progressively older genes are also activated with the increasing age of the animals. The same conclusion was reached in comparative analyses carried out on Drosphila , mosquitoes of the genus Anopheles and threadworms. These two studies throw new light on an age-old biological conundrum: that of the link between ontogeny and phylogeny. "Our discovery confirms the earlier anatomical studies and broadens our understanding of how development and evolution are linked at molecular level," explains Alex T. Kalinka, a researcher from the Dresden group. "The results show that the similarity between different animal species in the middle of their embryonic development is shaped by selection," adds Casey Bergmann, a co-author from the University of Manchester. Their findings explain how the "waist" in the hourglass arises. Fruit flies are one of the most thoroughly researched model organisms and offer unique possibilities for the study of the molecular mechanisms that underlie embryonic development. The discovery of the hourglass pattern in different species makes it possible for evolutionary biologists to travel back in time to the earliest days of evolution when the differences between organisms arose. "We hope to gain insight into the processes that led to the variety of forms in the animal kingdom," explains Pavel Tomancak. For their study on zebrafish, another model organism widely used in evolutionary biology, the researchers from Plön also developed a new method: the transcriptome age index (TAI). This method enables the measurement of the phylogenetic age of active genes. Domazet-Lošo and Tautz used this new tool to trace the development of the zebrafish from the fertilised egg to the adult organism. "The TAI profile faithfully reproduces the hourglass model and therefore demonstrates that parallels exist between ontogeny and phylogeny," reports Diethard Tautz. The scientists explain the observation that the phlogenetically oldest genes are active in older zebrafish with the fact that animals which have passed reproductive age are "overlooked" by selection. These studies show that naturalists like Karl von Baer, Charles Darwin and Ernst Haeckel were basically correct in their hypothesis that embryonic development is a reflection of phylogeny. "It will be very exciting to extend our approach to other species with different blueprints and life-cycle strategies," says Domazet-Lošo. Story Source: Materials provided by Max-Planck-Gesellschaft. Note: Content may be edited for style and length. What is the study of similarities and differences in the body structure of organisms?Comparative anatomy is the study of similarities and differences in the body structure of organisms. In comparison, the study of the function of those structures is known as physiology. These concepts are closely related to each other and can help find evolutionary relationships in different species.
What are embryo similarities?Embryos of many different kinds of animals: mammals, birds, reptiles, fish, etc. look very similar and it is often difficult to tell them apart. Many traits of one type of animal appear in the embryo of another type of animal. For example, fish embryos and human embryos both have gill slits.
What are some similarities in developing embryos to show how different species are related?Similarities in structure among distantly related species are analogous if they evolved independently in similar environments. They provide good evidence for natural selection. Examples of evidence from embryology which supports common ancestry include the tail and gill slits present in all early vertebrate embryos.
What does it mean when embryos of different species have similar features?Homologous structures
If two or more species share a unique physical trait they may all have inherited this trait from a common ancestor. Traits that are shared due to common ancestry are homologous structures. The similar bone arrangement of the human, bird, and whale forelimb is a structural homology.
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