How is embryology evidence for evolution?

Question

Please help it's for my homework (please no Wikipedia)

Answer 1

Embryology shows us the stages an organism goes through as it develops from a fertilized egg. When we look at the embryological development of different kinds of animals, we see distinct similarities. This makes us think that these different kinds of animals must have a common ancestor. See some pictures here:

http://www.hcc.hawaii.edu/~pine/book1qts/embryo-compare.jpg

Answer 2

The study of embryology is but one way to show that evolution is a viable theory. One of the first things that is covered is the three main embryonic germ layers:
1. The ectoderm generates the outer layer of the embryo. It produces the surface layer (epidermis) of the skin and forms the nerves.
2. The endoderm becomes the innermost layer of the embryo and produces the digestive tube and its associated organs (including the lungs).
3. The mesoderm becomes sandwiched between the ectoderm and endoderm. It generates the blood, heart, kidney, gonads, bones, and connective tissues.
These three layers are found in the embryos of all triploblastic (three-layer) organisms. Some phyla, such as the porifera (sponges), cnidarians (sea anemones, hydra, jellyfish), and ctenophores (comb jellies) lack a true mesoderm and are considered diploblastic animals.
Next embryoligists examined the development of fish, frogs, salamanders, fish, birds, and mammals, and emphasized the similarities in the development of all these vertebrate groups. Structures such as vertebrate pharyngeal arches, which become the gill apparatus of fish and become the mammalian jaws and ears, the formation of the vertebrate skull, the notochord, a rod of dorsal mesoderm that separates the embryo into right and left halves and tells the ectoderm above it to become the nervous system.
All vertebrate embryos (fish, reptiles, amphibians, birds, and mammals) begin with a basically similar structure.

Answer 3

First, similarities between embryos of related organisms:
E.g. (picture): http://www.evoled.org/docs/similarity.gif

And second, vestigial structures that appear in embryos, but disappear by full development. (Such as gill folds in mammal embryos, tails in human embryos, or leg buds in dolphin embryos ... as in the following):
http://www.talkorigins.org/faqs/comdesc/images/dolphin_embryo.jpg

BTW, many of people confuse (and dismiss) these as part of the discredited "recapitulation theory" of Haeckel. This is the famous "ontogeny recapitulates phylogeny" saying. Haeckel was overinterpreting the existing evidence to say that the development (ontogeny) of an embryo was a step-for-step "replay" of the evolutionary history (the phylogeny, or where the organism fits in the tree of life). While this is NOT true (many steps appear in the wrong order, or don't appear at all), there are still lots of structures that appear in embryos that have no function other than as a temporary expression of some latent genes that are hanging around in the genome of the embryo.

I have also heard the rather amazing claim by some creationists, that things like gill slits in an embryo are prefectly consistent with its aquatic environment in the womb ... which is astounding because it misses the point that these gill slits aren't actually used for *breathing*, but rather the embryo gets its oxygen from the umbilical cord.