http://wjmll.ncl.ac.uk/issue03/west_johnson.htm
"On the following page (p.10), 4000 BC is given as a date for
Indo-European, but this must be a terminus post quem non, for by 2000
BC the IE languages had diverged considerably. Whatever one's stance
on the Indo-Hittite hypothesis, the striking differences between
Hittite on the one hand and the Classical languages on the other
surely indicates that the split between the Anatolian languages and
the rest of IE must have been much earlier. While one can accept the
identification of the IE tribes with the Kurgan culture in the absence
of anything more compelling, one has to ask.why they moved from their
original homeland. The latest research connects this with the flooding
of the Black Sea basin ca. 5000 BC. But if this occasioned the spread
-- and therefore the split -- of IE, the proto-language itself must
have been earlier. The title of the section 2.1.1, "The Indo-European
family of languages (4000 - 2000 BC)", is therefore seriously misleading."
"The impression is given on p. 13 that PIE tribes migrated to the
Baltic Sea and became Germanic. There is no mention of the, perhaps
more plausible, idea advanced by Renfrew that populations remained
relatively static and that a new language was adopted by what were to
become the Germanic tribes by a process of cultural accretion.Of the
"three main differences between PIE and Primitive Germanic" (p. 13),
the accent shift could certainly be listed under this heading, but
ablaut cannot, as it is inherited from IE. The "third important
development" (p.14) is the First Sound Shift. What about the
developments in the vowel system, the sonants, the coalescence of the
palatals and the velars, the many other morphological changes?
Admittedly, the weak verbs are given brief mention on p. 14, but the
account is unbalanced and confusing, typified by the author's use of
terms such as "(not) inherited change" ("Another change which was not
inherited by the Romance languages was the shift of stress patterns
which occurred in Primitive Germanic" (p.14)."