For their study, García-Moreno and his team wanted to watch how brain circuitry develops. Using RNA sequencing and other techniques, they tracked cells in the palliums of chickens, mice and geckos at various embryonic stages to time-stamp when different types of neurons were generated and where they matured.

They found that the mature circuits looked remarkably alike across animals(opens a new tab), just as Karten and others had noted, but they were built differently, as Puelles had found. The circuits that composed the mammalian neocortex and the avian DVR developed at different times, in different orders and in different regions of the brain.

Still, it seems likely there was some inheritance from a common ancestor. In a third study that used deep learning, Kempynck and his co-author Nikolai Hecker found that mice, chickens and humans share some stretches of DNA(opens a new tab) that influence the development of the neocortex or DVR, suggesting that similar genetic tools are at work in both types of animals. And as previous studies had suggested, the research groups found that inhibitory neurons, or those that silence and modulate neural signals, were conserved across birds and mammals.