Taxonomy tells us that unlike the other three genera of the family, Hominidae, our Homo genus has only 46 chromosomes, not 48.
The smoking gun is that the great apes, consisting of genus Pongo (orangutans), Gorilla, and Pan (chimps and bonobos), have two chromosomes which, if we assume an ancient fusion event at the telomeres of the short (p) arms, gives us the telomere-telomere fused single human Chromosome #2.
Consider this image I downloaded from Facebook: we have the remnant of a centromere in the long arm of our chromosome where the middle of ape chromosome would have been and telomere remnants where the fusion took place in what is now the pericentromeric region of our long arm (2q).
End-to-end fusions are not uncommon in the genetic life of an our cells and are the result of telomere shortening and replicative senescence as I explain in this diagram from Telomere Timebombs: Defusing the Terror of Aging:
End-to-end fusions lead to breaks, mutations, and cell death by apoptosis. When this occurs in a stem cell line, dysfunction can ensue if apoptosis fails or the cell survives and replicates.
What is interesting is not that two chromosomes were joined to form one but why this splicing occurred. As Pope Francis said, God is not a magician and perhaps evolution is not inconsistent with intelligent design.
As Monty Python alum John Cleese recently Tweeted, science is a method, not a system of belief, and certainly not a blunt instrument meant to shame other possible viewpoints:
Maybe there was no divine splicer but maybe there was. Unless you were there, who can really say how and why humans diverged from their close relatives in chromosome number?
As I blogged about here in explaining rainbows and aging, we can understand the how without really grasping the why.