What caused the Pleistocene/Holocene extinction? Human hunters, or climate change?

[Blake]

@Colibri

One scenario, however, that has not been confirmed is Paul Martin’s extreme “blitzkrieg” hypothesis for the extinction event in the Americas due to the rapid expansion of Clovis hunters. It’s now pretty well established that the human presence in the Americas predates Clovis, and that humans co-existed with the megafauna for longer than had initially been supposed. The process may have been “sitzkrieg” (attrition) rather than blitzkrieg.

Myehhhh. I’m sceptical.

I’m sceptical firstly about the pre-Clovis hunters. The jury is still out though the evidence is weighing strongly in favour of their existence.

But if they did exist they clearly maintained a low population density to escape detection for so long. That tells me that something very odd was happening with this human population. Even at the conservative population densities seen in Australia or we have abundant evidence of human habitation from >10, 000 ybp suggesting that the pre-Clovis Americans were living at densities below even that.

Which then leads to the Bering invasion. These were modern people making a deliberate voyage of expansion and with constant contact with the homeland so no technology could be lost following settlement. These people exploded in population swamped the pre-Clovis and almost immediately left numerous and unmistakable signs of their existence. And within a millennium or so of the first signs of the Siberian arrival we see the megafaunal extinction. These were the people responsible for any blitzkreig.

So the blitzkrieg hypothesis isn’t really disproved even if pre-Clovis Americans are proved. The only difference is that we now have a pre-existing human population that didn’t or couldn’t exploit the environment effectively. That is an intriguing addition to the story but I have a hypothesis to explain that too.

My personal hypothesis is that they were an extremely isolated and unintentional colonistaion, possibly the result of a single Lapita/proto-Polynesian craft. As a result they were genetically very uniform but worse still they were unadapted to their environment and as a result went through a massive population bottleneck. That had the same effect that it had on the people of Tasmania, with a severe loss of technology. These pre-Clovis people lacked much of the technology associated with modern humans and were reduced to a basically Palaeolithic toolkit with no ability make clothing, rope or even fire.

At that reduced technology and genetic level they lacked the ability to recover their population rapidly or to even make any massive dent on the animal population. Indeed looking at the bizarre cultural twists taken by Tasmanian culture they may have been restricted largely to waterways and coastlines and never hunted large animals much. That would account for the low population densities and the concomitant lack of evidence.

But whatever the cause of the low pre-Clovis populations they were sparse and had little environmental impact in contrast the rapid reproduction to high densities seen by the later Siberian settlers. As such Martin’s blitzkrieg hypothesis isn’t in any way falsified by pre-Clovis Americans. At worst the hypothesis needs some minor modification

[MrDibble]

@ralph124c

And, how come humans never wiped out the African elephant?

Hey, we’re working on it! Elephant, Rhino, Whales, it’s all work, work, work here at Extinction Inc.

Or, to be more serious, you do know how close we came to wiping out elephant and rhino (and buffalo) completely before we developed the philosophy of conservation, don’t you? It’s the only thing that (may have) saved them.

[Colibri]

@Blake

But if they did exist they clearly maintained a low population density to escape detection for so long.

The evidence has always been there. The “Clovis-first” orthodoxy, however, has historically been so strong that it forced the dismissal out of hand of sites that would easily have been accepted if they had been dated later. Many of these sites are now being re-examined. I will, however, agree that pre-Clovis sites appear to indicate a much lower population density. (Although some of this could be due to these cultures preferring tools made out of perishable materials, such as wood.)

Which then leads to the Bering invasion. These were modern people making a deliberate voyage of expansion and with constant contact with the homeland so no technology could be lost following settlement.

There is actually no solid evidence that the Clovis culture itself came from Siberia. (Although genetic evidence indicates that recent Amerindian populations did originate in northeast Asia, this doesn’t mean that the Clovis culture did.) There is only one Clovis-style fluted point known from the Old World, and it is far from certain that it predates Clovis. It could even represent a back-colonization from the New World.

King and Slobodin say that Uptar “offers a tempting link” with the Paleoindian tradition. The origins of Clovis are debated, with opposing camps arguing either that it evolved out of a much earlier American tradition or that it developed quite rapidly from a Siberian tradition imported with early migrants just before 11,200 B.P. That the Uptar point might help clarify this matter and the date of the peopling of the New World (see “Colonizing the Americas”) is generating excitement among scholars.

But there are problems. Though the point must be older than 8300 B.P., as King and Slobodin observe, how much older remains undetermined. Uptar could be earlier than the Clovis sites, and its fluted point a progenitor of Clovis; contemporaneous with them; or even later, in which case the fluted point might have been invented in the New World and carried back to Siberia before the land bridge was submerged ca. 11,000 B.P. Unfortunately, the underlying sand and gravel are not easily dated, so it is unlikely that the age of the point will ever be known more precisely.

Furthermore, the Uptar collection differs in many respects from Clovis assemblages, and the fluted point is a far cry from the elegant Clovis points. It could even be a unique piece that was never part of a coherent tradition.

Although Clovis spread extremely rapidly throughout North and Central America, apparently within 300-500 years, it is also not clear that it spread from north to south.

From here (supported also by other material I have read that is not available online).

Clovis artifacts are widely and unevenly dispersed in North and Central America, with the cultural range apparently limited primarily by continental and mountain glaciers, lakes, and associated inhospitable terrain features. Clovis people definitely were not limited to or focused upon any specific geographic areas. Yet, Clovis points are notably more common in the Southern and Central plains than in the Northern Plains, and more Clovis artifacts come from the northern Great Basin and northwestern United States than the Northern Plains.

The notion that Clovis originated in or spread throughout North America from a point of origin in the Northern Plains (within an ice-free corridor between the continental glaciers) is not supported by the distribution of finds. Clovis may actually have spread from south to north across the Great Plains.

Clovis also did not penetrate South America, being found no further south than Panama. There is an analogous but different type of point, the fishtail, that was used by big-game hunters in South America. Clovis proponents have supposed that these fluted points were derived from Clovis, but there is no evidence to support that, and these points seem to be an indigenous South American tradition that spread from south to north. Both Clovis and fishtail points are found in Central America.

From here

The point is a “fishtail” form, several isolated examples of which have been found farther south in Central America, but which has come from dated contexts only in South America. As the oldest dated (ll,000 B. P.) context is at Fell’s Cave near the Straits of Magellan, and they appear soon thereafter in Buenos Aires Province on the Argentine pampas, it seems most reasonable to conclude that this distinctive form was developed in southern Patagonia as part of a local adaptation to hunting horses, and subsequently diffused northward after the horses became extinct.

. . .

The distribution of Clovis-like and fishtail fluted points in Central and South America is most parsimoniously explained by the hypothesis that Clovis fluted points, which are dated on the Great Plains and in south-eastern Arizona between l0,900 and 11,200 were diffusing southward from their North American centre at the same time the Magellanic fishtail form, which is dated in the southern cone between 11,000 and 10,500 B. P., was diffusing northward. The two technological traditions met and merged in Ecuador and Central America about 9,000 years ago. Furthermore, the localized distribution of early projectile points suggests that local people developed special techniques for hunting large game animals, including the idea of bifacial projectile points, which were experimented with and adopted if they proved to be effective. Hunting around lakeshores and in open grassland ecosystems such as the high parámos would explain the sparsity of early points in lowland forested areas of Central America.

@Blake

So the blitzkrieg hypothesis isn’t really disproved even if pre-Clovis Americans are proved.

What I mean by the “blitzkrieg hypothesis” is Martin’s original formulation of a wave of colonists bursting out Alaska and sweeping through the Americas from north to south. There supposedly was an exceptionally high population density at the front of this wave, and it was this high density that caused the megafaunal extinctions as it passed through. There doesn’t seem to be any real evidence that supports this scenario.

On the contrary, the timing of the development of fluted points in North and South America suggests an independent origin within existing populations, and subsequent spread culturally rather than through physical migration. The megafauna may have been killed off fairly rapidly by the spread of these hunting cultures, but it was in a manner different from that postulated by Martin’s blitzkrieg hypothesis.

@Blake

These pre-Clovis people lacked much of the technology associated with modern humans and were reduced to a basically Palaeolithic toolkit with no ability make clothing, rope or even fire.

This is clearly not so, at least if one accepts Monte Verde as a pre-Clovis site. Monte Verde includes a number of hearths, as well as animal-hide shelters which were tied to wooden supports with cords made from grass. (The Monte Verde site is a peat bog which preserved perishable material.) The people hunted small game and guanacos; there are also mammoth bones at the site, though it is uncertain whether these may have been scavenged or perhaps were just furniture. The inhabitants gathered shellfish at the coast more than 40 km away, and either collected or traded for medicinal plants that grew 160 km away. They had several kinds of flaked stone tools, as well as a variety of wooden and bone tools. Some grooved stones may represent bolas weights. Monte Verde clearly represents a rather complex and sophisticated culture.

@Blake

But whatever the cause of the low pre-Clovis populations they were sparse and had little environmental impact in contrast the rapid reproduction to high densities seen by the later Siberian settlers. As such Martin’s blitzkrieg hypothesis isn’t in any way falsified by pre-Clovis Americans. At worst the hypothesis needs some minor modification

While some of the lack of evidence of pre-Clovis sites may be due to the fact that they may have been concentrated in seacoast areas that are now submerged, in inland ares they do appear to have been pretty sparse compared to later populations. However, IMO the increase in population may have been due to a rapidly spreading cultural adaptation, possibly in response to changing environmental conditions at the end of the Pleistocene, rather than a mass migration through the hemisphere.