Augh! We're all going to be giant brains on the floor! Make it stop! Can't anyone make evolution stop!?!
No. But Edmond Hamilton can make it accelerate to a rate of fifty million evolutionary years for every fifteen minutes under the ill-conceived cosmic-ray lens. I've read a handful of Mr. Hamilton's stories, and I love their rough-cut disconnection from reality, especially the, uh, "science" part of reality. It seems that Hamilton did not let his tenuous grasp of any field of inquiry stand between him and a good yarn. I read this story when I was a kid (in Isaac Asimov's anthology The Golden Years, I think), and it made a big impression. I still think it's a lot of fun, with a few Gothic elements, including the complete destruction of the unholy site of the events and a survivor who ends up giggling mad in a sanitarium.
A fine adventure in the pulp tradition. Reminiscent of H.G. Wells's First Men in the Moon, but without the commentary on society. Interesting to note that the author, writing fully in the mindset of the time, did not grant the queen of the termites her rightful authority. As far as he was concerned, if there was a big brain running the termite society, it would have to be a guy.