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Vol.
XXVIII No. 45
November
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Our
Small Cousins: Rewriting Human Evolution
Prabir
Purkayastha
INDONESIAN
and Australian archaeologists (Nature, October 28, 2004) have found a set
of six small skeletons in a cave in the island of Flores, which is causing a
re-look at the humankinds evolutionary history. The surprise in the skeletons
is that they are only about 18,000 years old and indicate a group of humans
about 1 metre tall. Even more surprising, the brain size of this group: it is
about 380 cc, about one fourth the size of a normal human brain (normal sapiens
brain 1400 cc). Report indicates that there are bones in this group, which date
to as late as 13,000 years, long after all the other cousins of the Homo
sapiens (our species) is supposed to have died out. The differences of the
Flores Man (or more appropriately the Flores Woman as the skeleton which has
been used for classification is probably that of a woman) from all other known Homo
species are large enough to justify identifying it as a distinct species the
Homo Floresiensis.
Skull
of the Flores (Wo)Man Nature, October 28, 2004
POPULAR
PERCEPTION
The
popular view of evolution has tended to be that lower life forms evolve into
higher and higher life forms. Evolution, in this view, is something like
climbing a ladder. From this, the essentially anthropocentric view of evolution
that the end objective of evolution is the highest life form, our species, which
we named as Homo, the wise, our brutal history not withstanding. Against this
view, the palaeontologists have pointed out that in evolutionary terms, any
species that survives and multiplies itself for a historically large amount of
time is as successful as any other; there is no evolutionary ladder that is
being climbed by the species. In this view, the evolutionary schema is like a
tree, each branch/twig being a successful species. Even here, the extinction of
species and their survival is not so much being better but more suited to an
appropriate ecological niche and also due to accidental factors. For example,
there is evidence to show that the Homo sapiens came near extinction at
least once and this explains why a herd of 100 chimpanzees has more genetic
variations than the seven billion human population.
The
Flores discovery reinforces what is widely accepted, and shows that the bushy
character of the evolutionary tree holds good for Homo population as
well. We now have neanderthalensis and Floresiensis as cousins to
the Homo sapiens. And the Floresiensis was around well after the
Neanderthals became extinct.
FLORES
DISCOVERY
Why
should the discovery of a related human species draw so much attention? After
all, new large mammalian species have been discovered in recent times with
hardly a ripple. Contrast this with the amount of publicity that the Flores
discovery has generated. Obviously, we take ourselves quite seriously as a
species; therefore discovery of any new human kin is a matter of intense
curiosity. And the recent film version of Tolkeims The Lord of the Rings has
spurred this interest even further, most papers referring to the Flores (wo)man
as hobbit.
The
Flores discovery does raise some interesting questions. That it must have
descended from an originally larger species is obvious: all the known precursors
were much larger. That large species can become dwarfed in an island environment
is known. What is surprising is the decrease of the brain to the size of a grape
fruit: the reduction of the brain size was even sharper than the reduction of
the body size. And yet, from all evidence, Floresiensis used tools and
knew the use of fire. The reduction of brain size does not seem to have affected
its cognitive (thinking) abilities.
Island
dwarfism is a well-known phenomenon. If there are no large predators and there
is a limited supply of food, there is no evolutionary advantage to a larger body
size. In fact, a larger size requires higher food consumption and therefore is
in more danger in times when food is scarce. This island dwarfism works pretty
fast: the elephants in Malta and Sicily became one-fourth their size in a matter
of mere 5,000 years.
BRAIN
SIZE
IN
EVOLUTION
Why
did the brain also reduce in size and that also its reduction being even
sharper? In the Homonin family, brain size has got progressively bigger. The pithecines
brain (Australopithecus) was roughly the same size as the chimpanzee
brain. The erectus had brain size from about 650 cc to 1260 cc; the Homo
sapien brain is marginally larger than that of the Homo erectus.
Geniuses can have brain size of anything between 1000 to 2000 cc, and brain size
in humans has little to do with intelligence.
Big
brain is not an obvious evolutionary advantage. It requires high amounts of
energy (about 25% of our metabolism) and also high quality protein diet. One of
the reasons for increasing of meat in the early human diet was driven by
brains requirements high protein diet. So the shrinking of the brain in an
island situation where protein sources were limited could be an advantage. The
surprise is that in spite of its smaller size, it had superior tool making
capabilities than its ancestral erectus population. It is not size but
how it is used that counts.
While
the earlier version of evolution in which the human species is the final goal
has been given up, there has been a lot of hype on the brain size as a marker of
superior cognitive ability. It is routinely pointed out that how in the
evolution from pithecines to Homo sapiens, the brain size has
increased along with abilities such as tool making and speech.
It now appears that mere increase in brain size has less to do with its
abilities. It does appear that the shrinking of the Floresiensis brain
did not lead to any significant reduction in cognitive abilities. And if we
accept that the finds in nearby caves of small tools as also those used by the
Flores (wo)man, then we have to accept that they show a superior tool making
ability than the erectus population who had a brain size ranging between
650 to 1260 cc. The quality of these tools is considerably higher than what is
known to be associated with the erectus population. There is some doubt
about who were the toolmakers of these tools. They were found in another section
of the cave from that where the six Floresiensis skeletons have been
discovered. The Nature authors have placed this firmly as the
achievements of the Floresiensis, and not of later Homo sapiens.
Did
the Floresiensis (wo)man have a language? It is possible that Homo Floresiensis
had limited language capabilities, though some of the authors of the papers in Nature
have contended that with the evidence of hunting as groups, the Floresiensis
must also have had language. Without a clearer idea on what caused the increase
in brain size and well it correlates to language development, it will remain an
open issue.
Flores’
inhabitants have incredibly detailed legends about the existence of little
people on the island they call Ebu Gogo. The islanders describe Ebu Gogo as
being about one metre tall, hairy and prone to “murmuring” to each
other in some form of language. If this evidence is accepted, then not only did
the Floresiensis use tools and fire, they even had speech, with a brain
size of a chimpanzee. No wonder this find is causing a hard re-look at some of
our theories of the brain and its evolution.
Image
from National Geographic Reconstruction based on skull data and a good deal of
imagination
If
we look at the human family tree, our earliest ancestors diverged from the
chimpanzee lineage about 7 million years ago in Africa. The homonins were about
1 to 1.5 metres, walked upright and had brains the same size as that of the
chimpanzee. The erectus population appeared about 2 million years back
and spread across all the continents. Though the Floresiensis skulls do
not resemble the erectus skulls markedly, the hypothesis is that the erectus
ancestors travelled by rafts or boats to the island of Flores and the Floresiensis
population descended from them. Between Java and Flores is the Wallace line; a
land bridge from Java to Flores could not have existed even then and therefore
the need for sea-crossings, something the more archaic erectus were
thought not being capable of.
OUT
OF AFRICA
THEORIES
OF EVOLUTION
What
does the Floresiensis do to the other controversy of multi-regional and
Out of Africa theories of evolution of the Homo sapiens? The Out of
Africa theory, based on genetic data, posits that Homo sapiens evolved in Africa
about 160,000 years back and spread out from Africa about 100,00 years ago. All
the current races are descended from this African population. The multi regional
theory, claimed significant differences amongst races, with local populations
evolving over time to Homo sapiens with some gene flows across population
groups. The gene flows across groups was to ensure that it still remained one
species in spite of distinct evolutionary paths of the different races. The
genetic data has shown that Out of Africa represents the real evolutionary path
and is now almost universally accepted, except amongst some die-hard proponents
of the multi-regional thesis. The Floresiensis now again shows that the
intermixing of population was very rare and most groups would have evolved in
different directions rather than a common Homo sapiens path. However, the
Out of Africa theory does not really need this added support, the genetic
evidence is just too strong for any other hypothesis to be even a possible
contender today. All that can be disputed is whether some marginal gene flows
took place when the modern Homo sapiens spread out from Africa. This is
not going to change the big picture; the entire human species are non-resident
Africans, give or take at most a few genes.
There
is still the possibility, though unlikely that there may be extant small
populations of isolated human cousins of ours: the yeti or other similar
mysterious creatures. But the more likely scenario is that the Homo sapiens
have driven all other species of Homo to extinction, with Floresiensis
being added to the Neanderthals. It is only that our complete global dominance
is shorter than we thought.
