> American paddlefish (Polyodon spathula), which are diploid, have 60 pairs of chromosomes, while Russian sturgeons (Acipenser gueldenstaedtii), which are tetraploid, have four sets totaling about 250 chromosomes (the chromosomes are so numerous and some are so small that it’s hard to count them reliably). Nearly 200 million years of independent evolution should have seeded the two species’ DNA with countless genetic mismatches and incompatibilities — from missing and added genes, to rearrangements and relocations of genes, to mutational tweaks to gene expression. It seemed certain that hybrid cells would struggle to figure out how to line up their chromosomes during cell division and what genes to turn on or off.

As the researchers said:

> “We never wanted to play around with hybridization,” said Mozsár. “It was just a negative control, which found, somehow, a way to live.”