Introduction

Embryonic homology refers to the underlying similarity that arises from the structures being derived from a common ancestral structure. This concept is important in evolutionary embryology and has been distinguished from analogy, which refers to structures that are similar in function but not in ancestry.

Homology and Analogy

Homologous structures are organs that are similar in both structure and ancestry. The wing of a bird and the arm of a human, for example, are homologous structures, having evolved from the forelimb bones of a common ancestor. On the other hand, analogous structures are those that are similar in function but not in ancestry. For example, the wing of a butterfly and the wing of a bird are analogous structures, as they perform a similar function (flight) but do not share a common ancestral structure.

Developmental Change and Evolutionary Change

Evolutionary change is based on developmental change, as seen in the formation of the bat wing. The bat wing differs from that of a bird because of changes in gene activation during embryonic development. Mice and humans, for example, have webbing between their digits, which serves an important function in creating the distinction between the fingers. In bats, however, genetic signals prevent cell death in the webbing and accelerate finger elongation, allowing the fingers to be used for flight. This change in development provides the variation needed for evolutionary change.

Artificial Selection

Artificial selection, as observed in pigeon and dog breeds, provides valuable resources for studying selectable variation. For example, the short legs of dachshunds were selected by breeders for use in hunting badgers. The mutation that causes the short legs is due to an extra copy of the Fgf4 gene, which informs cartilage precursor cells to stop dividing earlier than in most other dogs, resulting in shorter legs. Similarly, long-haired dachshunds differ from their short-haired relatives due to a mutation in the Fgf5 gene, which is involved in hair production and allows each follicle to make a longer hair shaft.

Conclusion

In conclusion, embryonic homology refers to the underlying similarity in structure and ancestry of homologous structures. Analogy refers to structures that are similar in function but not in ancestry. Evolutionary change is based on developmental change, as seen in the formation of the bat wing. Artificial selection provides valuable resources for studying selectable variation, as seen in the differences in pigeon and dog breeds. Mutations in genes controlling developmental processes can generate selectable variation, as seen in the differences in dachshund breeds.