Why “late equals large” does not work

The concept of conservative scaling of mammalian brain subdivision size with respect to brain size is one of the more contentious issues in neuromorphological studies. What is generally less critically discussed is the widely-cited suggestion that a highly conserved neurogenetic sequence during brain development is the reason for this conservative scaling and other processes of mammalian brain evolution. Here I re-visit the data with which the influential notion of conserved neurogenesis and mechanistic relationship between neurogenesis and mammalian brain subdivision scaling was developed. I suggest that neurogenetic sequences in the species available are not particularly conserved, and that brain subdivision sizes do not correspond well with neurogenetic sequence timing. As an alternative, I propose favouring less generalized and more heterochrony-focused approaches of relating timing differences between species to adult morphology.