Inferential evidence for evolution is evidence that does not involve direct observation of evolution but from which we can infer that evolution has occurred. The three main kinds of inferential evidence for common descent are contemporary homologies
, biogeography, and the fossil record. Inferential evidence is open to interpretation, but this doesn’t mean inferential evidence is weak. The more such evidence that exists and the less any alternatives can explain it all, the stronger evolution is.
Homology has a specific meaning in evolution, but I will not be using that to avoid circular reasoning — we can't "prove" evolution using terms that assume evolution. I will use a more general meaning for homology: similarities between species that are not functionally necessary. In pre-evolutionary terms, the alternative type of similarity would be an analogous similarity: the wings of birds and bats are similar, but this can be explained by their similar function. This is an analogous similarity. In a homologous similarity or homology, the similarity cannot be easily explained or explained at all functionally.
Biogeography is the study of the the distribution of life forms over geographical areas. Biogeography not only provides significant inferential evidence for evolution and common descent, but it also provides what creationists like to deny is possible in evolution: testable predictions. Biogeography is split into two areas: ecological biogeography which is concerned with current distribution patterns and historical biogeography which is concerned with long-term and large-scale distributions.
Creationists like to pretend to know something about science, but usually just end up demonstrating their ignorance. One good example is the attempt to 'prove' that evolution is incompatible with science, an attempt which involves distorted and outlandish definitions of science not actually used by anyone who works in the science. The definitions sound good to the ignorant, though.
that show intermediate characteristics are called transitional fossils
- they have characteristics that are intermediate in nature to organisms that existed both prior to it and after it. Transitional fossils are strongly suggestive of evolution because they indicate the progression of from just as evolutionary theory predicts. Transitional fossils are frequently misunderstood, and like macroevolution, creationists tend to redefine the term to suit their purposes.
When you hear talk of evidence for evolution, the first thing that frequently comes to mind for most people are fossils. The fossil record has one important, unique characteristic: it is our only actual glimpse into the past where common descent is proposed to have taken place. As such it provides invaluable evidence for common descent. The fossil record is not "complete" (fossilization
is a rare event, so this is to be expected), but there is still a wealth of fossil information.
Our idea that there can even be such a thing as a “missing link” was created in an era of biological research which is long gone. It’s a concept which is no longer valid in our current understanding of the nature of life and evolution — but, as is so often the case with appealing concepts, it continues to live on, to structure people’s assumptions, and to influence how they think about evolution.