[lutusp]

> The theory in this case is "Isolations affects alcohol tolerance in crayfish".

That is not a theory, it's a statement about an observation -- it describes, it doesn't explain. Theories explain observations.

> A theory does not need to contain an explanation to be a valid scientific theory.

A scientific theory is an explanation[1]. That's how it's defined. A description cannot be a theory because it doesn't say why the result took place, only that it did.

If I say, “The night sky is filled with tiny points of light,” I've offered a description. Another observer might contradict my description, for example by emerging from his cave on an overcast night and not seeing any points of light, but that contradicting observation can itself be contradicted on the next clear night, without any chance for resolution (so a contradiction is not a falsification). Apart from being shallow, inconclusive and trivial, this process is not science.

If instead I say, “Those points of light are distant thermonuclear furnaces like our sun,” I've offered an explanation, one that makes predictions about phenomena not yet observed and that's falsifiable by empirical test. On the basis of this explanation we might build a small-scale star (a fusion reactor) to see if our experiment shows any similarity to the spectra and behavior of stars. This deep explanation represents a theoretical claim that's linked to other areas of human knowledge, predicts phenomena not yet observed and is conclusively falsifiable by comparison with reality (our fusion reactor might fail to imitate the stars). It's science.

1. https://en.wikipedia.org/wiki/Scientific_theory

Quote: "A scientific theory is an explanation of some aspect of the natural world that can, in accordance with the scientific method, be repeatedly tested, using a predefined protocol of observations and experiments. Established scientific theories have withstood rigorous scrutiny and are a comprehensive form of scientific knowledge." (emphasis added)

[benchaney]

"Isolation affects alcohol tolerance in crayfish" is not just an observation. An observation would be "Crayfish #5 has behavior X".

You are conflating two different definitions of explain. It is possible to explain what is happening without explaining how. It is possible to know that A causes B without knowing why (This is purpose of the scientific method). If it were actually impossible to have evidence that something is true without knowing why it is true, than it would be impossible to have evidence of anything at all. You could invalidate any knowledge by just asking "why", because there is always another "why". To give an example, we know that mass causes gravitational attraction even though we don't fully understand the mechanism that causes it.

[lutusp]

> It is possible to explain what is happening without explaining how.

That's a description -- an account of what was observed. By definition, an explanation must add something to a description.

"The night sky is filled with points of light." -- a description.

"Those points are distant thermonuclear furnaces, powered by atomic fusion." -- an explanation.

"Similar bird species have differently shaped beaks." -- a description.

"Bird species evolve traits that confer a survival advantage in their distinct environments." -- an explanation.

> It is possible to know that A causes B without knowing why ..."

One cannot claim to know that A causes B without also knowing why, otherwise puddles cause rain. Science is not merely about knowing -- it's about knowing that we know. An observation asserts a fact without context. A scientific theory offers more than mere description, and its standing rests solely on the fact that it has resisted falsification.

> To give an example, we know that mass causes gravitational attraction even though we don't fully understand the mechanism that causes it.

Yes, but that's not a scientific theory, it's a description -- mass causes gravitational attraction, or equivalently, gravitational attraction causes mass (my point is the claim is wrong but without a theory, we can't know that it's wrong). As long as there's no testable theory, the two descriptions are equivalent.

The Greeks believed our sight resulted from our eyes shooting beams out into the environment. Until we had a testable theory, no one could reasonably dispute that idea.

A theory is not a description -- it offers more than an account of observed facts. The water rises across the beach over a period of hours: a description. The sun and moon apply tidal forces -- a spatial differential in gravitational force -- to the water, causing it to periodically rise and fall: an explanation, one that can be tested and potentially falsified.