The earlier studies tended to estimate a relatively long time-frame for
the development of the different branches. In particular the study by
Bouckaert and colleagues (which included a geographical element) was
"decisively" in favour of Anatolia as the geographical origin, and
supported Colin Renfrew's hypothesis that Indo-European spread from
Anatolia along with agriculture from 7,500–6,000 BCE onwards.
According to their analysis, the five major Indo-European subfamilies –
Celtic, Germanic, Italic, Balto-Slavic and Indo-Iranian – all emerged as
distinct lineages between 4000 and 2000 BCE. The authors pointed out
that this time-scale is consistent with secondary movements such as
the expansion of the steppe peoples after 3,000 BCE, which they
suggest also played a role in the spread of Indo-European languages.
However, the more recent study by Chang, Cathcart, Hall, and Garrett
(2015) came to a different conclusion. Their analysis differed from the
earlier ones by using only languages which have a known historical
ancestor such as Old English, Latin, Ancient Greek, and Sanskrit, to take
account of the fact that languages develop at different rates; they also
included other methodological refinements to eliminate possible
biasses of earlier studies. The results support a rather shorter timescale
for the development of IE and are consistent with the Steppe
hypothesis.
According to Kassian et al. (2021), Hittite was the earliest language to
split off from the rest, around 4,139–3,450 BCE, followed by Tocharian
around 3,727–2,262 BCE. Subsequently Indo-European split into four
branches ca. 3,357–2,162 BCE: (1) Greek-Armenian, (2) Albanian, (3)
Italic-Germanic-Celtic, (4) Balto-Slavic–Indo-Iranian. Balto-Slavic split
from Indo-Iranian around 2,723–1,790 BCE, Italic-Germanic-Celtic broke
up around 2,655–1,537 BCE, and Indo-Iranian split up around 2,044–
1,458 BCE. The position of Albanian, in fact, is not completely clear,
from an insufficiency of evidence.