[mannykannot]

This, however, provides no explanation for the decline in population prior to the first European contact, as the author is claiming that DNA evidence suggests this was not going on prior to the arrival of Europeans. The author also claims that there was no pre-European decline, yet presents before-and-then estimates that are only consistent with that at the extremes of their ranges. In general, the argument being presented here is rather incoherent.

[justinator]

Just a theory, but is it possible that there was previous contact that wasn't as well documented?

One theory posited by people like Charles C. Mann is that the native population of say, North America were drastically reduced before the likes of English colonizers came onto the scene by infectious diseases.

Maybe, maybe not (and maybe that happened well after)

[mannykannot]

It would think that is possible, but the author seems to be claiming otherwise in the third-from-last paragraph.

One consideration (not raised in the article) is that perhaps the people of South America (unlike the Polynesians) did not have the seagoing technology or know-how to make a round trip to the island, prior to the arrival of europeans.

The English were relative latecomers among the European colonists of the americas, and by then smallpox and other diseases had spread widely. Apparently, the Wampanoag had suffered from an epidemic, now suspected to have been smallpox, in the years prior to the arrival of the Mayflower Pilgrims in 1620.

https://en.wikipedia.org/wiki/Wampanoag