Cross-breeding is insufficient to explain speciation because the first two speciation events of life (i.e. abiogenesis and then the 2nd species to form) had no such cross-breeding options.
Further, the author of this article is claiming that mutations and new species are more possible with 10,000 pre-humans than with 6 billion modern humans.
That dog won’t hunt. For that matter, even the “isolation leads to speciation” theory fails to explain why pigeons in Australia are the same as pigeons in New York City or London. It’s not like they’ve been flying across oceans to breed for the past million years...
But it doesn't. There are perfect examples of speciation from isolation still living -- with all of the intermediate forms (transitionals, or "missing links") still in place!
Just google "ring species!"
Ring species provide unusual and valuable situations in which we can observe two species and the intermediate forms connecting them. In a ring species:
- A ring of populations encircles an area of unsuitable habitat.
- At one location in the ring of populations, two distinct forms coexist without interbreeding, and hence are different species.
- Around the rest of the ring, the traits of one of these species change gradually, through intermediate populations, into the traits of the second species.
A ring species, therefore, is a ring of populations in which there is only one place where two distinct species meet. Ernst Mayr called ring species "the perfect demonstration of speciation" because they show a range of intermediate forms between two species. They allow us to use variation in space to infer how changes occurred over time. This approach is especially powerful when we can reconstruct the biogeographical history of a ring species, as has been done in two cases. Source