Which weighs more, a pound of monkeys or a pound of dust? Trick question: a pound is a pound is a pound. So, in the final scene of the play, which has Drummond holding the Bible in one hand and Darwin in the other, shows that the two books, and the two belief systems they represent, should get equal weight:
([. . .] DRUMMOND is left alone on stage. Suddenly he notices RACHEL's copy of Darwin on the table.)
DRUMMOND (Calling) Say—you forgot—
(But RACHEL and CATES are out of earshot. He weighs the volume in his hand; this one book has been the center of the whirlwind. Then DRUMMOND notices the Bible, on the JUDGE's bench. He picks up the Bible in his other hand, he looks from one volume to the other, balancing them thoughtfully, as if his hands were scales. He half-smiles, half-shrugs. Then DRUMMOND slaps the two books together and jams them in his brief case, side by side. Slowly, he climbs to the street level and crosses the empty square.) (III, 721-35)
The image of the scale is an old symbol for justice, because justice requires balance in order to work. (No, we're not talking about the digital kind that tells you when you overate; we're talking about the old-fashioned kind with two hanging dishes…)
The last scene of Inherit the Wind lets us know that Drummond believes both sides should be treated fairly. But it isn't clear whether he believes that these two sides are necessarily equal. Drummond's definitely on the side of teaching evolution in the schools, so you might think he would give Darwin a little extra weight; but maybe he's just showing that you can't only know one side of the story.
Both sides are always necessary for a complete sense of the truth.