In an effort to establish agreement on a common set of facts, I offer the fact of biological evolution as a touchstone of truth within science. I will try to explain how we know evolution is true, and why it matters. Biological evolution is, in a few words, descent with modification; or, if you like, change within the gene pool of breeding populations over time. Evolution explains how all existing organisms, including humans, came to be; thus, it is deeply important in our understanding of how the world works. As a scientific theory, it continues to be refined and elaborated; but the basic truth of it is well-established and powerfully explanatory. Evolution even provides a useful template for understanding change over time in non-biological systems. We should all be able to agree on the truth of evolution.
We know evolution is true in all the ways we use science to know anything is true. The theory of evolution is consistent with all observations about living systems, and it explains and predicts biological phenomena. There are multiple, converging lines of evidence that evolution is true, including the fossil record, genetics, molecular biology, morphology and comparative anatomy, biogeography, direct observation, and more. The theory of evolution is falsifiable, but has never been falsified. Evolution is so powerfully explanatory that it has been said that nothing in biology makes any sense except in the light of evolution; and no other theory of “the origin of species” is remotely as demonstrably valid as evolution.
Evolution involves differential reproductive rates for organisms as a function of which individuals are best adapted to the existing environmental conditions (selective pressures). When environmental conditions change, species can evolve over time into new species; but this typically takes many generations, and so can be difficult to observe directly in species with long life spans. In recent decades, biologists have used species with very short life spans directly to observe evolution.
Along with providing a large part of the picture of how the world works, evolution has important practical lessons for us. One lesson is that all of life is interconnected by ancestry at least; we are in nature, not outside of nature. Thus it is in our survival interests to maintain biodiversity as much as we can, to keep our distant relatives vibrant in case we need their help. Evolution informs our strategies in fields such as medicine, agriculture, and conservation, helping us survive and prosper.
For all the reasons discussed, it is important to agree on the truth of evolution. As the evidence confirming evolution continues to pour in, we have an ever firmer basis for constructive public discussion and public policies. Building on a base of truth established by science, we can avoid wasteful controversies and ineffective activities. This will, in turn, serve as a model for extending the base of agreed-upon facts to promote civil discourse and enlightened action.
Speaking of "civil discourse", profanity will not be accepted in comments. Fair warning...