How is embryology used in classification

A cow is more like a sheep than it is like a fish. So phenotypic appearance is important i. Similarities between extant and extinct creatures are more difficult: we are unlikely to see a modern human foot on a fossil human ancestor: but it is still recognisably a foot, and so are the feet of dinosaurs.

The foot is an homologous structure i. We have said that the wing of a bird is not homologous with the wing of an insect. These do the same thing, but not in the same way: they are analogous.

Often a similar feature arises more than once: the wing of a bat is not descended from the wing of a bird: are they analogous? Are they homologous No, not quite because one did not descend from the other. They are examples of convergent evolution, nearly homologous because each is homologous with the forelimb of some non-flying ancestor.

Sometimes homologous structures are so modified that it is difficult to see the similarity. What do we do then? When talking about different animal groups I gave you a clue: some animals have similar larvae, i. We now reach a point where we have to define terms. First of all lets look at evolution and development. In fact these terms are quite mixed up in laymen's language. Going to the O.

Theory of E that the embryo is not created by fecundation, but developed from a pre-existing form ; origination of species by development from earliest forms. So evolution, in non scientific terms, means both the development of an individual and the development of a species. And development covers evolution too. Are these two the same thing? If not how are they related? Why are they considered to be related at all?

Well, earlier, pre-evolutionary views certainly fit well with this idea of evolution as unfolding, like a scroll. There was a widespread view that all human bodies were created fully formed but rolled up, as it were, in the ovaries of Eve.

A complementary theory described the homunculus, perfectly formed, rolled up in every sperm. The other view of evolution, as progressive change through time is usually attributed to Darwin, but he, interestingly, only uses the word once in the Origin of the Species - then it is the last word in the book. There are perfectly good reasons for distinguishing the two developments, or the two evolutions, one of the organism the other of the species. For instance the eggs of many but not all animals are separated into soma and germa.

The soma develops into the body of the individual: the germa goes on to form the gametes, future generations. Modifications in the soma somatic mutation, teratogens will not affect the species but will affect the operation of the genetic program during an animal's lifetime: mutations in the germa will not influence the development of the current generation but may influence the future of the species.

These two processes have, of course long been distinguished. The development of an individual from fertilisation to maturity is ontogeny : the development of a species or lineage is phylogeny. The idea of a relationship between phylogeny and ontogeny is an old one, but was probably crystallised by looking at embryos of different species.

These all look suspiciously alike, and the younger the embryos the more similar they look. Throughout chapter thirteen, Darwin cites examples to support his conclusions on vestigial organs.

One of those examples includes the remnants of legs on snakes. Snakes do not use legs to move, yet some of them possess structures similar to legs; they are in the same location as the legs of other species, and they are composed of the same basic parts, although smaller.

Naturalists correlated the rudimentary legs of snakes and the functional legs of lizards. Darwin uses these examples to critique the theory of creationism. Darwin asks: why would individually and uniquely created species have useless structures? Darwin says that, if we accept creationism to explain the origin of species, then we must accept that there is no rational explanation for these parts. In contrast, natural selection explains those phenomena.

Organisms possess vestigial structures because they have an ancestor that also possessed these structures. Those structures in descendent species adapted for different functions, or disappeared due to selective environmental pressures, which their ancestors did not experience.

Darwin's embryological arguments for evolution influenced the study of the relationships between evolution and development. For example, after the publication of The Origin, Ernst Haeckel in Jena, Germany, used Darwin's arguments in support of his biogenetic law or recapitulation, which stated that organisms replay their evolutionary ancestry while developing from embryos to adults.

Many biologists accepted Haeckel's biogenetic law until the s. Darwin By: M. Elizabeth Barnes. Keywords: recapitulation theory , von Baer's Laws. Sources Baer, Karl Ernst von. Beobachtung und reflexion. Observations and Reflections]. Bowler, Peter J. Evolution: The History of an Idea. Costa, James T. The Annotated Origin. Cambridge: Harvard University Press, Darwin, Charles R. London: John Murray Publishing House, Linnaeus, Carl. Systema Naturae [System of Nature], 12th edition.

Holmiae: Laurentii Salvii, — Gould, Stephen J. Ontogeny and Phylogeny. Cambridge: Harvard University Press , Haeckel, Ernst. Generelle morphologie der organismen.

Berlin: G. Since the heyday of Darwinism, considerable scientific evidence has emerged supporting the theory of evolution, including embryology, although the mechanisms of mutation and change are more complex than previously understood. Theories, such as the theory of evolution, are evidence-based ideas widely held by the scientific community. According to Charles Darwin in Origin of the Species , organisms descend and diversify from one common ancestor.

Organisms change and adapt over time as a result of inherited physical and behavioral characteristics that are passed down from parent to offspring. Through the process of natural selection and survival of the fittest, certain traits are more likely to be inherited than other traits. Embryology is the study and analysis of embryos.

Evidence of an evolutionary common ancestor is seen in the similarity of embryos in markedly different species. Darwin used the science of embryology to support his conclusions. Embryos and the development of embryos of various species within a class are similar even if their adult forms look nothing alike. For instance, chicken embryos and human embryos look similar in the first few stages of embryonic development. These early similarities are attributed to the 60 percent of protein-coding genes that humans and chickens inherited from a common ancestor.

Kowalevsky suggested that sea squirts called tunicates should be classified as chordates instead of mollusks because tunicate larvae have notochords and form neural tubes, making them more like chordates and vertebrate embryos.