Robert J. Sawyer wrote a series of sf books called The Neanderthal Parallax which proposes that human sentience (and Neanderthal sentience) originated, and ende

Robert J. Sawyer wrote a series of sf books called The Neanderthal Parallax which proposes that human sentience (and Neanderthal sentience) originated, and ended, with changes in the Earth's magnetic field. It explored some very interesting social and anthropological ideas. https://en.wikipedia.org/wiki/The_Neanderthal_Parallax https://en.wikipedia.org/wiki/The_Neanderthal_Parallax