split from their common ancestor or when they migrated from Africa. This
determination is the gist of our argumentation. For the past 15 years, the speed
of the molecular clock has been estimated in terms of the number of mutational
differences in matching segments of DNA between humans and primates based
on the fossil records. The speed has been assumed to be rather high. Thus,
according to this phylogenetic mutation rate, it has been supposed that the Out-
of-Africa dispersal of Homo sapiens occurred 70 kya at the earliest (Oppenh eimer
2012, Gibbon s 2012). A new method of obtaining the mutation rate that has
recently been developed calculates the mutation rate of the entire genome of
present-day humans by counting the number of new mutations in the nuclear
DNA of a newborn baby compared with its parents (Gibbon s 2013). The value
that Scally and Durbin (2012) cite is 0.5× 10 –^9 bp–^1 year–^1 , which they claim is
half of the previous fossil-calibrated phylogenetic rate. In other words, the
molecular clock ticks more slowly than previously assumed. The calculation based
on this new rate shifts the Out-of-Africa migration of modern humans to 90–130
(rather than less than 70) kya (Scally and Du rbin 2012, Gibbons 2012).^13
Second, based on genetic polymorphisms and cranial shape variables of modern
human populations from Africa and Asia, Reyes-Centeno et al. (2014) claim
support for a multiple-dispersal model in which only Australo-Melanesian popu-
lations are isolated descendants of an early migration, whereas other Asian
populations are from members of subsequent dispersal events. The researchers
note that their results support an initial exodus out of Africa into Asia by a
coastal route along the Arabian Peninsula beginning as early as 130 kya and a
later migration wave into northern Eurasia starting by 50 kya.
Interestingly, the number resulting from recent genetic studies (i.e., 130 kya)
nicely matches the number obtained from the arguments developed in the
preceding section based on archaeological/paleoanthropological evidence from
stone tools and fossils.^14
In sum, recent archaeological/paleoanthropological evidence and genetic
evidence converge to reasonably conclude that the Out-of-Africa dispersal of
Homo sapiens occurred much earlier than previously hypothesized, that is, as
early as or at the latest 130 kya.^15 Hence, based on the simplest hypothesis
noted above, I propose that human Merge/UG emerged (at the latest) around
130–150 kya in East Africa.^16 This is the hypothesis of an earlier emergence of
the human language faculty (see also Ike-uchi 2012, 2014).
4 A pos sible scenario
According to our hypothesis of an earlier emergence of the human language
faculty, the scenario of the emergence of Merge/UG and the Out-of-Africa dis-
persal is as follows (Ike-uchi 2014). First, due to genetic mutation, Merge/UG
emerged in the brain of one individual member of a certain group of Homo sapiens
in (North) East Africa (at the latest) approximately 130–150 kya. Merge/UG
subsequently spread among a certain number of people in that group (but not
necessarily among all the people in the group at that time) as a result of natural
192 Masayuki Ike-uchi