Why would anyone think that? The evolutionist would reject it out of hand. The creationist would reject it on biblical and scientific grounds. The concept of original sin is lost if there is more than one Adam and Eve, and there is no need for more than 1 pair of initial ancestors to produce the (fairly limited) genetic diversity that we see today.
Once a species exists, however it got put there, nothing keeps it from evolving variations. The biggest differences between humans are only micro-evolutionary steps apart.
Land bridges existed sufficiently short times ago that mankind doesn’t need to be more than several tens of thousands of years old to be able to explain how it got to everywhere it did. There could have been early hominids superficially “like” humans as we know them, for example the Neandertal, but none of them would need to have been the source of mankind.
A & E were created separately and specifically. It doesn't mean they were the ONLY ones, just special.