Biology Reference
In-Depth Information
ies, australopithecines that lived millions of years ago (the famous Lucy,
for example) had a smaller RBS than modern people. In fact, the RBS
of australopithecines was very similar to that of living chimpanzees.
Humans therefore have brains that are over three times the sizes of both
australopithecines and apes of similar body mass, because evolution
pulled the RBS of our ancestors to a whole new level.
Homo erectus
was
evolutionarily and temporally intermediary between australopithecines
and humans, and so was its RBS, which was twice that of apes and aus-
early hominins to have a larger average RBS than their ancestors had.
Applying these principles to
Homo floresiensis,
we expected LB1, who
lived a mere 18,000 years ago, to have evolved an RBS that was greater
than her ancestors'. If, as some believed, she was descended directly
from
Homo erectus,
her RBS should have been greater than twice the
average RBS for chimpanzees and australopithecines. One might also
have predicted that her RBS would have been larger than that of
Homo
erectus
for the same reasons that human pygmies have a larger average
RBS than their bigger-bodied cousins. To our surprise, the RBS of LB1
turned out to be considerably
smaller
than the best estimates of RBS
for
Homo erectus.
With a cranial capacity of 417 cm
3
and a body weight
estimated to be between 30 and 35 kg (66-
77 lbs.), Hobbit's RBS fell
bode well for LB1 being an island-dwarfed descendant of
Homo erectus.
As an alternative possibility, we concluded our paper with the sugges-
tion that “
H. erectus
and
H. floresiensis
may have shared a common ances-
tor that was an unknown small-bodied and small-brained hominin.”
26
We could not completely rule out the insular-dwarfism hypothesis,
however, for the simple reason that no one really knew if the scaling
principles described above apply to animals that become dwarfed on
islands. Is there something about living in harsh island environments
that causes RBS to veer from its predicted path when animals become
dwarfed? A hint that RBS sometimes scales in unexpected ways ap-
peared nearly 70 years ago when the renowned paleontologist Franz
