People's Democracy

 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 humankind’s 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 Tolkeim’s 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 brain’s 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.