Who wrote the short story with the climax/resolution/denouement "It only stands to reason"?

This is "A Voice Is Heard in Ramah ..." by Spider Robinson, first published in Analog, November 1975 and subsequently appearing in several of the Callahan collections.

The background for Callahan's (the eponymous bar of the series) is that periodically they have competitions for the worst pun; this scene takes place on one of those nights.

Long-Drink led off, his eyes filled with that terrible gleam that presages a true stinker. They call him Long-Drink because he is one long drink of water; when he sits he looks like he's standing, and when he stands he looks like three other guys. He doesn't mass much more than a pickup truck, and he's the only man I know who can talk and drink whiskey at the same time. He does a lot of both.

"Gentlemen," he drawled, demonstrating the trick, "the story I am about to relate takes place in the distant future. Interstellar travel is commonplace; contacts with aliens are familiar experiences. One day, however, a planet is discovered out Antares way whose sole inhabitant is an enormous humanoid, three miles high and made of granite. At first it is mistaken for an immense statue left by some vanished race of giants, for it squats motionless on a yellow plain, exhibiting no outward sign of life. It has legs, but never rises to walk on them. It has a mouth, but never eats or speaks. It has what appears to be a perfectly functional brain, the size of a four-story condominium, but the organ lies dormant, electrochemical activity at a standstill. Yet it lives.

"This puzzles the hell out of the scientists, who try everything they can to get some sign of life from the behemoth-in vain. It just squats, motionless and seemingly thoughtless, until one day a xenobiologist, frustrated beyond endurance, screams, 'How could evolution give legs, mouth and brain to a creature that doesn't use them?'

"It happens that he's the first one to ask a direct question in the thing's presence-it rises with a thunderous rumble to its full height, scattering the clouds, thinks for a second, booms, 'IT COULDN'T,' and squats down again.

"'Migod,' exclaims the xenobiologist, 'Of course! It only stands to reason.'"

There was an extended pause, in which the sound of Long-Drink blinking was plainly audible. Then a hailstorm of glasses, full and empty, burst in the fireplace, loud enough to drown out the collective groan. Doc Webster's eyes rolled briefly, like loaded dice, and came up snake eyes. Callahan began passing out fresh drinks with a slightly stunned expression.