Unsuitable 'blanket statement' title now moderated., page-139

This is not true. This is a really complex topic [1], but many different species can interbreed and produce fertile offspring.

On this topic, all the gene flow from Neanderthals appears to have come in from female hybrid offspring (the male African/Neanderthal hybrids appear to have been infertile). This follows Haldane’s rule [2] and is the same as seen with Ligers.

1. https://en.wikipedia.org/wiki/Species
2. https://en.wikipedia.org/wiki/Haldane's_rule