1. Darwin, the producer of natural selection, kept his "fourth category of evidence" morphology, as the "very soul of natural history." Just as organisms are characterized by families, orders, or generas Darwin contributed his theory of morphology as the starting point of an organisms mutation/ evolution.
2. The organisms mutation/ evolution can be traced through the "number of shared characteristics between any one species and another which indicates how recently those two species have diverged from a shared lineage." This lineage was unexplained until Richard Owen, a friend of Darwin's, made the great contribution by advancing the concept of homologues- "superficially different but fundamentally similar versions of a single organ or trait, shared by dissimilar species."
ie. five- digit skeletal structure of the vertebrate hand appears not just in humans and apes but also variously modified in cats and bats and lizards and turtles.
Internet: In traditional systems of taxonomy, classifications were based on the morphological characteristics of organisms. However, a method of classification based purely on morphology runs the risk of grouping together organisms that are actually relatively unrelated but have evolved similar features. In more modern systems of taxonomy, the genetic similarity of organisms, studied through the methods of molecular biology, is considered in addition to morphology when establishing taxa.
A taxon (plural taxa), or taxonomic unit, is a name designating an organism or group of organisms
http://www.thefreedictionary.com/morphology
3. Morphology was Darwins fourth category of evidence. Darwin described it as the "very soul" of natural history. Zoo's describe just how easily living creatures can be sorted into hierarchy of categories, based on which anatomical characters they share and which they don't. Morphologists such as Georges Cuvier, Etienne Geoffroy Saint-Hilaire, and Richard Owen improved classification with their meticulous studies of internal and external anatomies. Today the same four branches of biological science embrace an ever growing body of supporting data. With these categories we have made new ones such as, population genetics, biochemistry, molecular biology, and the most recent genomics.
Most biologists, before Darwin, saw thenselves classifying most species by resemblance. For example, a whale resembles a fish in habit and basic apperance, but are from distant relatives (www.springerlink.com/index/V5WP5578329542R6.pdf).
4. Vestigal characteristics are a form on morphology evidence because they show characteristics that were once useful in former creatures. For example, "why to men have nipples"? It shows that humans have morphed and men have no use for their nipples.
5. Darwin drew out four branches of biological science, which were biogeography, palenontology, embryology, and morphology. The world of science has grown to have more branches: population genetics, biochemistry, molcular biology, and genomics.
Other Source: "Morphology is the branch of biology that deals with the form and sturcture of organisms without consideration of the function." (www.dictionary.com)
6. Living creatures can be easily sorted into a dierarchy of categories- not just species but genera, families, orders, whole kingdoms- based on which anatomical characters they share and which they don't.
7. Richard Owen advanced the concept of homologues. An example of this concept would be the 5-digit skeletal structyre of the vertebrate hand not just appearing in human hands, but apes, raccoons, bears, cats, bats, lizards and turtles (variously modified, of course).
"We have seen that the members of the same class, independently of their habits of life, resemble each other in the general plan of their organisation. This resemblance is often expressed by the term “unity of type”; or by saying that the several parts and organs in the different species of the class are homologous. The whole subject is included under the general term of Morphology." (http://www.bartleby.com/11/1404.html).
