I suspect part of it is also that the distinction between recent brands of humanoids have narrowed down as we get closer to us, so the distinction between homo sapiens sapiens and homo sapiens is less than the distinction between homo sapiens and homo heidelbergensis, while the difference is bigger yet from homo heidelbergensis to homo erectus.
The longer time they existed may well be an effect of classifying more of them as being part of the same species rather than being a result of actually being the same for longer.
Reductionist and proud of it.
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