How about Conan Doyle, or whoever it was, does not make the Piltdown Man hoax in 1912.
At this point, the oldest purported hominid is the Javan
Homo erectus, from which there is no complete cranium available. In 1921, the Broken Hill cranium is found and
Homo rhodesiensis receives the attention it deserves, since there is no Piltdown Man to back the British establishment's "wells, why would man come from Africa when we have evidence right here that it hails from next to London"
rolleyes
. BH's comparative small cranium and teeth also draws contrary lessons to Piltdown's big brain and big teeth, and in 1925
Australopithecus is seriously considered, if not outright accepted as the oldest known hominid, and as a result Raymond Dart is not shun for 20 years. This leads to a surge in human fossil hunts to South Africa which results in the earlier discovery of
Paranthropus (OTL 1938) and maybe
Homo habilis (OTL 1949, but not named/recognized until the discoveries in East Africa of the 1960s).
There is even a getaway explanation for the racist preconceived ideas of the time that made people refuse to consider Africa the craddle of humanity. "Weee, South Africa is almost European in climate, so it makes sense that apes would become men there, and not in some torrid backwards area like Ethiopia or Kenya or Tanzania you know".
This has massive repercussions in paleoanthropology and accelerates knowledge of early hominids by decades. It's historical repercussions outside of that? Next to zero. People would think of Mrs. Ples or the Taung Child rather than Lucy when told to think of a pre-
Homo hominid. Leakey would still make his discoveries in East Africa from the 1960s onward, since he was born and raised in Kenya, but they won't be seen as revolutionary or be as heavily featured in paleoanthropology books. Oh, and creationists would lack a convenient straw man to bring up when attacking human evolution and ignore all the actual evidence, but I suppose they would just use the Nebraska Man instead.