In more recent years, however, there's been a revisionist movement, powered partly by geneticists and partly by archaeologists, to show that British populations - along with some aspects of their culture, such as funerary arrangements, survived in English areas. The speaker last night was a linguist, and he was making a pretty powerful restatemenet of the traditional case, based in large part on comparisons with other cases of invasion and the various kinds of linguistic interchange that took place (or didn't): e.g. the British in India, the British in Australia, the Normans in England, the French in North Africa. Different things seem to be implied by the amount and type of vocabulary that gets exchanged, the direction of travel, whether any grammatical features are shared, and the fate of place=names. For example, the fact that so many Cornish place names survive, by contrast with British names in England (and especially the dearth of British place names in the south and east) suggests a different kind of invasion in that region - which was brought under English rule several centuries later - perhaps with the Anglo-Saxons setting up an elite overlordship, rather than wiping the natives out.
So, my question is quite simple. Why did Anglo-Saxon war leaders go around in pairs? Hengist and Horsa, Aelle and Cissa - but you never hear about shared Anglo-Saxon kingship? And what were the practical arrangements for running an army with two generals?