The metatarsal of Callao Man is reported to have been reliably dated by uranium-series dating to 67,000 years ago[22] thereby replacing the Tabon Man of Palawan, carbon-dated to around 24,000 years ago,[23][24] as the oldest human remains found in the archipelago. Negritos were among the archipelago's earliest inhabitants, but their appearance in the Philippines has not been reliably dated.[25] There are several opposing theories regarding the origins of ancient Filipinos. F. Landa Jocano theorizes that the ancestors of the Filipinos evolved locally. Wilhelm Solheim's Island Origin Theory[26] postulates that the peopling of the archipelago transpired via trade networks originating in the antediluvian Sundaland area around 48000 to 5000 BCE rather than by wide-scale migration. The Austronesian Expansion Theory states that Malayo-Polynesians coming from Taiwan began migrating to the Philippines around 4000 BCE, displacing earlier arrivals.[27][28] Whatever the case, by 1000 BCE the inhabitants of the archipelago had developed into four kinds of social groups: hunter-gathering tribes, warrior societies, highland plutocracies, and maritime-centered harbor principalities.[29]