The tolerance isn't explained. The duplication is.

Every mammal that's ever been checked, humans included, builds every antibody it makes off one genetic locus — one stretch of DNA holding the heavy-chain genes that get shuffled and recombined into an antibody's business end. A paper published this year in Science Advances found that vesper bats don't. The vesper family is the largest group of bats there is, more than 500 species, found on every continent except Antarctica, and the team found two separate heavy-chain loci in them — not a redundant backup copy of the same genes, but two genetically and functionally distinct sets, doing different jobs. Nothing like it had been documented in a mammal before.

The finding has a real backstory worth keeping: the same result first went up as a preprint in August 2024, under nearly the same title, and sat there for almost two years before this year's peer-reviewed version. Whatever slowed it down, it wasn't the finding losing anyone's interest — the lead researcher, Hannah Frank of Tulane University, put it plainly once it was out: “We've never seen anything like this in a mammal before. This completely changes our understanding of how mammalian immune systems can be organized.”

The honest gap is Frank's own, stated in the same breath as the result: a second antibody system is not, by itself, why bats famously carry viruses that would put most other mammals in the ground. “It doesn't fully explain why bats are such effective viral reservoirs,” she said, “but it reveals a level of immune variety we didn't know existed, and gives us an entirely new direction to explore.” That's the right-sized claim: a new, real structure in a genome, not a solved mystery wearing a new finding as an explanation. This site draws its own share of plant immune systems (the Venus flytrap's touch count, the ant that guards a leaf's extrafloral nectary) — worth remembering that the animal case for "built differently than we assumed" is just as real, and just as unfinished.

Source: Pursell, Reers, Mikelov, Kotagiri, Lam, Ellison, Boyd & Frank, Immunoglobulin heavy chain locus duplication in bats, Science Advances 12(31) (2026), doi:10.1126/sciadv.aeb6714.