There was a discussion of the concept of evidence on one of the forums I post to, so I posted the following analysis.
Evidence is a body of observations that have been logically integrated to their cause. I will give an illustration using one of Jerry Coyne’s lines of evidence for the theory of evolution in Why Evolution is True.
According to Coyne, the species of animals found on islands near continents bear significant similarities to the animals on the mainland, but they differ from the animals on the mainland in ways that allow them to fill the specific niches available on the island, and the only species of animals found on the island are ones small enough to be blown by the wind or carried on driftwood to the island. Therefore, they must have been carried from the mainland to the island and evolved into a variety of new species once there.
Let’s take this apart into its components.
First, Coyne’s argument depends on observation. Scientists had to make countless measurements of species that live on islands near a continent and the species on the nearby mainlands to arrive at this conclusion. For example, in one case, they had to measure the beaks of birds on the island to show that they were adapted to eating nuts as opposed to the beaks of the birds on the mainland.
Second, Coyne’s argument integrates these observations. The observations are put together into a coherent whole that encompasses the fact that the species on the island are similar to the species on the mainland, the fact that there are specific niches on the islands that these species have adapted to fill, and the fact that the species on the island are all relatively small or have the ability to swim. These are all made part of a unified narrative.
Third, Coyne’s argument integrates these observations in accordance with logic. Coyne does not appeal to mysticism to explain the observations he cites, and he does not invent his explanation out of whole cloth. Rather, he logically infers the conclusion that is necessitated by the available facts.
Finally, Coyne’s argument logically integrates these observations to their cause. Causality is an entity acting according to its identity. Coyne’s argument reveals that the observations he cites are all manifestations of entities acting in an orderly fashion, according to their identities. The only entities that get to the islands are the ones that have the ability to do so due to their size or ability to fly or swim, and the only entities that survive on the islands are the ones that are adapted to fill the available niches, in obedience to causality.
I hope this has helped clarify the concept of evidence for you.