According to a theory advanced
by researcher Paul Martin, the wave
of species extinctions that occurred
Line in North America about 11,000 years
(5) ago, at the end of the Pleistocene era,
can be directly attributed to the arrival
of humans, i.e., the Paleoindians, who
were ancestors of modern Native
Americans. However, anthropologist
(10) Shepard Krech points out that large
animal species vanished even in areas
where there is no evidence to demon-
strate that Paleoindians hunted them.
Nor were extinctions confined to large
(15) animals: small animals, plants, and
insects disappeared, presumably not
all through human consumption. Krech
also contradicts Martin’s exclusion of
climatic change as an explanation by
(20) asserting that widespread climatic
change did indeed occur at the end of
the Pleistocene. Still, Krech attributes
secondary if not primary responsibility
for the extinctions to the Paleoindians,
(25) arguing that humans have produced
local extinctions elsewhere. But,
according to historian Richard White,
even the attribution of secondary
responsibility may not be supported
(30) by the evidence. White observes that
Martin’s thesis depends on coinciding
dates for the arrival of humans and the
decline of large animal species, and
Krech, though aware that the dates
(35) are controversial, does not challenge
them; yet recent archaeological
discoveries are providing evidence
that the date of human arrival was
much earlier than 11,000 years ago.
“Still, Krech attributes
secondary if not primary responsibility
for the extinctions to the Paleoindians,
(25) arguing that humans have produced
local extinctions elsewhere. ”这句话是什么意思，什么叫secondary if not primary ，后面argue的这个evidence是K的观点么？
secondary if not primary responsibility
for the extinctions to the Paleoindians,
(25) arguing that humans have produced
local extinctions elsewhere. ”这句话是什么意思，什么叫secondary if not primary ，后面argue的这个evidence是K的观点么？ | 
