How is embryology used to explain evolutionary relationships?

Answer 1

Embryology: In the first few days of development, a human embryo looks very similar to that of any other animal. After a few weeks, we can tell it's a vertebrate animal, but it doesn't yet look human - it could be a fish embryo! After a few more weeks, it looks like a mammal embryo, but we can't tell which mammal... and so on. Embryos of different species look very much alike in their early stages. The later on the embryos begin to look different, the more closely related the two species are. Further evidence comes when we look at some of the features embryos possess in their early stages. For example, at one point, human embryos have gill slits, like a fish (although never functioning gills), then later on a long tail, like most animals, then a yolk sac, like the eggs of birds and reptiles, and later still we become covered in fur like most mammals which we shed. Why would humans go through phases with gill slits, tails, yolk sacs and fur if none of these features are of any use to the adult? It's because our ancestors at one point had gills, tails, eggs with yolks, and fur (not at the same time, though!) We humans have kept those genes, and while they're inactive in adults, their effects show through at an early stage in development. And it's not just humans - embryonic snakes grow legs, which they lose, and horses grow five toes, of which four eventually shrink leaving behind the single hoof.

Answer 2

Darwin believed that the similarities found in embryos were a good indicator of what their ancestors looked like. However, Darwin did not accept this view, instead he supported the views of VonBaer who felt that required earlier in a character evolution tend to develop earlier in an embryo.

Answer 3

Through studying embryos, scientists have found that vertebrate animals seem to have a common design, even though their adult forms are different. Arm buds on different species, for example, look the same early on during embryonic development, yet they will develop into very different forms in the adult (a flipper, an arm, a wing, etc).

Answer 4

Embryological development shows the same set of nested hierarchies that every other feature of living things does, from their genomes to their behaviour. This pattern of nested similarities and differences is indicative of common descent.

On top of that, embryological development often produces atavistic features that aren't found in the adult form, but are found in more basal forms of the same lineage. An example of this is the pharyngeal arches found in embryological stages of human beings. At one stage, they are indistinguishable from the structures that form gill pouches in other animals - but in mammals, they develop into other structures. Another example is the hind limbs on whales: at some stage during the embryological development of a whale, the embryo forms hind leg limb buds, the same as embryos of the land-based animals from which it descended. Often, such buds are then reabsorbed. Many whales, however, retain some vestigial form of their hind leg bones.

Answer 5

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