Though it was based on very little evidence, many scientists thought that all mammalian brains, including the human brain, were made in the same way, with a number of neurons that was always proportional to the size of the brain.
Encara que es basaven en poques evidencies, molts científics creien  que tots els cervells de mamífers, incloent el cervell humà, estaven fets de la mateixa manera: amb un nombre de neurones que sempre era proporcional a la mida del cervell.