How is Darwin's theory called a theory?

Answer 1

His first paper was titled:-

'On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection'

His book was titled

'On the Origin of Species by Means of Natural Selection, or The Preservation of Favoured Races in the Struggle for Life' (usually abbreviated to On the Origin of Species).

In these publications he set described things/features that could be seen in the biological world and presented a process by which these could arise over time, with evidence to support these proposals. As such his publications conform to the scientific method and may be called a theory.

His proposals are now well accepted as being a correct/true description about how the variety of life as we know it came to be on our planet and form the basis of modern evolutionary theory. *In scientific terminology, a theory is a proposal/explanation with evidence that could be defended (a fossil record, the different bird specie variations, etc.) and an idea that can be used to predict further developments; in this case, that there have been/are/will be major changes to an organism's DNA/RNA over time as it adapts to its environment, which can be proven with a decent microscope and some bacteria, and common acceptance in the scientific community (tick this box).

Answer 2

Natural selection is a theory because it had been tested and verified countless times by experimentation and observation. It made accurate predictions and can be modelled mathematically. It is thus a scientific theory.

If you're wondering by any chance what a theory is in science, it is exactly what I described what natural selection went through. A scientific theory is a tested and verified hypothesis supported by evidence that explains a phenomenon we observe. Some examples of scientific theories are the theory of gravity, the theory of relativity, the germ theory of disease, theory of quantum mechanics, so on.

Here is what a theory is NOT. It is NOT a wild guess, opinion or speculation, unsupported by evidence, as the everyday term of theory would me. A theory in science is a very high status. It means the theory had passed through rigorious tests and were peer reviewed by many other scientists and accepted.