He doesn’t say “It makes no difference… whether humans arose by evolution or by a sudden act of creation”, as if humans could only have emerged through evolution or through creation, but not both.
He says “It makes no difference… whether humans arose at first by slow evolution or by a sudden act of creation”. In other words, his emphasis is “It doesn’t matter which humans came first, humans by evolution or humans by creation”. Saying that the first humans arose by evolution, does not say that no humans arose by de novo creation.
The first humans arising by evolution and other humans arising by de novo creation, are not mutually exclusive; the same applies to the reverse. This is why he can present more than one original pair as an option.
But let’s put it this way.
- Does your GAE require the first human pair to have evolved?
- Does your GAE require the first human pair to have been created de novo?
- Does it make no difference to your GAE if the first human pair evolved, or was created de novo?
Humans emerging through evolution, and a de novo created pair of humans, interbreeding between the two, and a genealogical descent of all humans from an ancestral pair, isn’t the GAE?
I think it’s clear that’s exactly what he’s doing. If that were the case, why would he even mention evolution in the first place, especially in the context of creation? Why would he mention the relevance of genealogical descent to Adam and Noah?
If he wasn’t concerned with origins, he wouldn’t have included a section explicitly on origins, specifically addressing the extremely hotly debated theological topic of his day. He obviously accepts evolution, for a start.
If you want to say he wasn’t originally concerned with origins, I would agree. If you want to say his work wasn’t written with the intention of settling origin questions, I would agree. But if you say he had this idea but never considered any of the consequences, or theological implications, I would strongly disagree.
If you read his original article, which contains even more theological content (published before he wrote the book, which is a much expanded version), it’s clear that he discovered a genealogical fact and then saw how it applied to a whole range of issues. He says explicitly “The close kinship of mankind especially in the same nation has an important bearing on one or two points of theology”.
So he came across this genealogical idea, saw how it applied to a range of theological and social issues, and then explained how it applied: to current theological discussions of the origin of humans, to the Christian concept of the brotherhood of man, to current social issues such as slavery, economic injustice, and hereditary titles and authority.