These cats come into contact in western and central Asia. Pallas’s cats are named for Peter Simon Pallas (1741-1811), the German naturalist who first described them to science. Darwin (1868, vol. 1, p. 45) says
The large Angora or Persian cat is the most distinct in structure and habits of all the domestic breeds; and is believed by Pallas, but on no distinct evidence, to be descended from the F. manul of middle Asia.
Though the two are considered distinct breeds today, in the 19th century Persians and Angoras were generally regarded as belonging to the same breed. Thus, in 1903, Frances Simpson wrote in her book The Book of the Cat,
In classing all long-haired cats as Persians I may be wrong, but the distinctions, apparently with hardly any difference, between Angoras and Persians are of so fine a nature that I must be pardoned if I ignore the class of cat commonly called Angora.
The name Persian cat may be significant, given that F. manul does occur in Persia (modern Iran), and Pallas’s cats do have fluffy hair like a Persian cat, which suits them to the cold, high-altitude environments in which they are typically found. But Pallas actually said not just that he thought the Persian is derived from this cross, but also provided the additional bit of information that they “easily mate” (or, perhaps, since the original Latin coëat is ambiguous “easily unite to produce offspring”). The passage in question appears in Pallas’s Zoogeographia Russo-Asiatica (1831, p. 23):
Its [i.e., F. manul’s] proportions, manner, and noble gait, lead me to suspect that this wild species is the source of the breed known as the Angora cat, which has fluffy hair, and which was domesticated even by the Chinese. Though differing in many ways from the domestic cat, when it is tame, the two easily mate.” Translated by E.M. McCarthy. Original Latin: “Proportiones habitus et altior ingressus suspicionem mihi movent ab hac fera specie ortam esse Felem sic dictam angorensem, pilo sericeo lanatam, quae etiam apud Sinas domestica datur. Multis enim haec a Cato differ, licet mansueta cum hoc facile coëat.”