Yeah, cloning was done before the 40s, but when was the idea of cloning humans really something anyone was talking about? ... Hang on, let's pull up Google Ngrams for this. Comparing ``cloned human'' to ``cloned animal'' (and I have no explanation for the 1900-1910 range):

Here's the 1900-to-1960 era. Meanwhile, open that up to the rest of the 20th century:

... and, basically, people thought a lot about cloning humans after 1960, but before then?

I guess my question is when did human clones start turning up in science fiction?