He certainly understood that a new species of humans took over after something went wrong with a prior species. The disappearance of the Neanderthals is perhaps one of the greatest mysteries in human evolution. And Swedenborg, who died in 1772, could not have any knowledge of this anthropological situation. (The first Neanderthal skull was discovered in the 1850s and it was much later before its significance in human evolutionary history was known.)
Swedenborg claimed that a race of human beings who were cerebellum-focused was replaced by a race of humans who became cerebrum-focused (with more developed foreheads). The reason he gives as to the extinction of this former race is purely spiritual—and it had nothing to do with species competition or environmental factors.
This prior race of humans (who were actually a different genus), were ruled by their involuntary brain or cerebellum (Neanderthal skulls show a protrusion or “bun” at the posterior lobe). While the cerebellum is a primitive part of the brain, Swedenborg maintained that this human brain received its forces, actions and modes directly from God’s heaven. Originally, this human race could converse with angels, and their breathing action was similar to heavenly rhythms. (Neanderthals also have a curious chest structure—with no waist.)
The design flaw of this race of cerebellum-focused humans was that they could not think differently from their involuntary nature and passions. Their cerebrums (and thoughts) concurred with the compulsions and orders of their hindbrains. When they eventually turned from God and adopted more self-centered and evil principles, they were unable to intellectually reflect on or challenge their passions. Furthermore, this caused their heavenly breathing rhythm to struggle and finally to stop. Their extinction was due to suffocation!
According to Swedenborg, the Lord God of heaven “changed the wiring” of some of these early humans and adapted them towards growing and using their cerebrums apart from their cerebellums. This allowed “modern” humans to appear—humans who could better accumulate knowledge from the physical world of the senses and learn about values (from external sources) that were nobler than their base intentions.
I share more intriguing details (and scientific support) about Swedenborg’s anthropological insights in my award-winning book Proving God.