There are, however, many problems with this model.Significantly, though a few sites are quite impressive, there really is very little archaeological evidence to support it.Writing in 1982, Martin himself admitted the paucity of evidence;for example, at that point, the remains of only 38 individual mammoths had been found at Clovis sites. In the years since, few additional mammoths have been added to the list;there are still fewer than 20 Clovis sites where the remains of one or more mammoths have been recovered, a minuscule proportion of the millions that necessarily would have had to have been slaughtered within the overkill scenario.

请问，老师这里的would have had to是虚拟语气吗？为什么？