If even the splitting of mammalian germ cells is not certain:
Meiosis is essential to sexual reproduction. For almost 15 years, it has been commonly held that retinoic acid, a molecule derived from vitamin A, triggers meiosis in mammalian germ cells. Yet new research demonstrates that meiosis in mice begins and proceeds normally even in the absence of retinoic acid. These findings set the stage for new research in the field of reproductive biology…
These twin studies therefore refute the dogma of a retinoic acid trigger for meiosis in germ cells, ending a debate that has lasted nearly a decade and a half. By dismissing a long-held tenet, these findings invite the scientific community to reconsider its working assumptions and investigate new leads in the search for the real signals controlling initiation of germ cell meiosis.CNRS, “Cell reproduction dogma challenged” at ScienceDaily
… maybe the 21st century would be better suited to questions in science than answers. It’s easier to get good answers when we have enough knowledge to get the questions right.