Reality never intrudes for you, does it? Humans are born with 24 chromosome pairs all the time. They are always sterile. You want hypothesize that two such freaks are going to be born that are not sterile, close enough in time and distance to find each other; and that they would have some competitive advantage over normal humans. It doesn't happen among humans or rats or mice; or fruit-flies despite the efforts of scientists world-wide bombarding the poor insects with radiation and trying to mate the mutants
ML/NJ
Chromosomal and genomic analysis shows that human chromosome 2 looks exactly like a fusion of two smaller chromosomes (present as two chromosomes in every other ape)including a degraded centromere sequence.
The observed chromosomal fusions and breakages, resulting in different chromosome number that we see in some individuals (something you claimed didn't even exist), is both necessary and sufficient to explain how such chromosome numbers can change in species sharing a recent common ancestor.
Well said.