Human Evolution in Remote Places

In the last twenty years, the lineage of modern humans has been widely accepted as complete. Several genus of Homo are recognized beginning with Homo habilis around 2.4 million years ago (Jones et. al 242) and ending with anatomically modern humans, around 130,000 years ago (251). It was not until four years ago, when the discovery of a small, fossilized skull, found on the remote Indonesian island of Flores, that the whole field of anthropology was thrown for a loop. The diminutive size of this skull has led some scientists to declare the emergence of a new species, Homo floresiensis, while other scientists state the specimen is the deformed skull of a modern human. These two theories have generated much controversy, and it has sparked a debate about how much change one species must endure before another lineage is classified as a new species. Randomly assigning a genus a new species just to increase the self-worth of some scientist’s want of academic praise from their colleagues is egocentric; without sufficient evidence it is irresponsible of a scientific community that is expected to carefully examine the data before taking such a drastic steps.

The discovery of a new species on a remote island is rare, but it has been known to show up in the archaeological record. The isolation of some islands have long been a spark for life to evolve abnormally because of the limitations surrounding the species’ environment. An excellent example of this is the island of Madagascar, an island off the coast of East Africa, and home to the world’s entire population of indigenous lemurs. The isolation of a species from the mainland is what scientists term genetic drift, the basic idea of which is “the random change of gene frequencies over time. It can take place rapidly in small populations, such as those on isolated islands, but happens in all populations regardless of size” (463). While this concept is present in all species and environments, genetic drift seems to effect isolated island populations more often because they have been cut-off from the mainland and must find another way to adapt to their new environment. This sudden adaptation can result in a slow change in a species over time, or a rapid one, depending on the species and environment.

The island chain of Indonesia in Southeast Asia is a prime example for isolated species to rapidly alter its physical appearance, although it is more common in the mammalian kingdom than the primate. It may be a coincidence, but in the same cave, on the same island that Homo floresiensis remains were found, fossils from a rare species of pygmy elephants, pygmy Stegodon, were also found. According to Van Den Bergh et. al: “At Liang Bua, evidence for S. f. insularis dates to between 95 and 12 ka (thousands of years), and is associated with high concentrations of stone artefacts and the skeletal remains of Homo floresiensis” (1). The association of stone artifacts and cut marks found on the animal bones has led some scientists to declare this cave site as a place where H. floresiensis butchered their kills, which would explain the high concentration of the Stegodon bones. Of course, the butchering of Stegodon would not explain why H. floresiensis disappeared around the same time as their pygmy elephant victims. Van Den Bergh also addresses this issue:

The disappearance of Stegodon from the Liang Bua sequence coincides
with a layer of fine-grained white tuff deposited in the cave around 11ka.
The associated volcanic eruption and environmental disruption may have
been a factor in the extinction of both Stegodon and H. floresiensis. (2)

Volcanic eruptions are common in that part of the world, and Van Den Bergh and his colleagues confirmed evidence of one occurring around 12,000 years BP (before present). It is possible that this eruption wiped out the island’s species of Homo and pygmy elephant, but that still does not confirm the evidence of a new species of Homo; for that, one must examine the fossil record of hominids and their geographical distributions over the past 2.4 million years.

The fossil hominid record is extensive and not always agreed upon in the anthropological community. The morphology that separate one species from another are often so minor, some scientists would argue they were not new species at all, but they were simply an extinct species with some abnormality, hence the debate over H. floresiensis. The human family tree, referred to as a clade, once thought to consist of a few species within a few genera, now has no less than twenty species belonging to at least four genera.

The diversity of fossil hominids’ cranial and post-cranial morphologies makes each species unique, and it is what classifies them into a multitude of taxa (any defined unit- species, genus, family and order- in the classification of organisms. Jones et al. 471). Many scientists argue over this recent suggestion of organizing the hominid clade, but as Cela-Conde and Ayala explain, “A genus is supposed to be monophyletic; that is to say it must contain only species that form a clade” (7685). They go on to explain that, “This is an unrealistic taxonomic expectation, given the fact that phylogeny is a continuum, with the exception of terminal twigs or extant taxa” (7685). Therefore, according to Cela-Conde and Ayala, some genus should not be considered monophyletic (a complete set of organisms derived from one ancestral stock) (Jones et al. 467) because of the diversity found among fossil hominids; they instead, must be categorized into their own genus and species to accurately support the fossil evidence.

It should be noted that the phylogenetic tree proposed by Cela-Conde and Ayala is based on the morphological and adaptive traits of each genera and species. Some genera, such as Praeanthropus, inhabited tropical forests and walked upright, while other hominids developed traits to adapt to their diets, like the thin enamel on the molars of Ardipithecus. As we move up the family tree, the comparison between the robust “masticatory apparatus” (7687), the muscles that aid in chewing on the skulls of Australopithecus robustus/A. boisei enable them to crush hard nuts and tough vegetation with their massive molars; while the more gracile skull and mandible of the genus Homo, shows evidence of a diet consisting of meat and other sources of protein. This particular adaptation eventually led to a larger cranium to protect brains that were important when it came to developing lithic (stone tool) technology, culture, organizational skills and an abundance of other traits that make Homo sapiens the dominant species in the world today.

While all these adaptive traits and morphological features show how species differ, it does not account for how a species, of previously unknown Homo origins, managed to arrive on a tiny island, thousands of miles from where Homo sapiens originated. The dispersal patterns of the hominid family are well known; from Africa to Europe to Asia to the Americas, hominids have been, for the most part, predictable. Finding a fossil hominid on a remote Indonesian island, with no explanation as to how it got there or why it looked different, was puzzling until a group of scientists led by Dr. Teuku Jacob of Gadjah Mada University Faculty of Medicine in Yogyakarta, Indonesia, examined the skull and limb bones of the H. floresiensis, nicknamed Flo.

Dr. Jacob and his colleagues concluded “that Flo was a pygmy Homo sapiens with a stature about 7 inches taller than previously estimated” (Bower 330). Furthermore, “Flo displays skull and limb abnormalities that resulted from a still-enigmatic, genetic growth disorder” (330). The data found in these examinations performed by Dr. Jacob et al. have spread doubt over this new species find, and it has led to numerous debates between respected anthropologists across the world. Some scientists may have dismissed Dr. Jacob’s observations if large amounts of H. floresiensis fossils were found, but so far the original evidence “include only one skull and two lower-jaw bones, along with scattered lower-body remains from a handful of individuals” (330). Bower contends that the lack of substantial evidence to support the original findings is hardly enough to declare a new species, and the remains are within the body-to-brain size range of Flores pygmies who still reside around the area where the fossils were found. Not only are they almost the same height, according to anthropologist Robert B. Eckhardt, but as Bower states:

Flo’s discovers used a mathematical formula for estimating stature that
shortchanged her height, Eckhardt contends. Flo, also referred to as LB1,
stood an inch or two shy of 4 feet, according to his team’s adjusted
calculations. This revised height gives a brain-to-height ratio that suggests
that Flo suffered from an as-yet unspecified growth disorder that included
microcephaly, a genetic condition that results in an unusually small head
and brain. (330)

These findings are the center of a heated debate, and some claim microcephaly is the reason for H. floresiensis’ small skull. Dr. Robert D. Martin et al. have done extensive research in this area and have concluded, among other things, that “the features of LB1 best support the interpretation that it is a pathological, microcephalic dwarf specimen of Homo sapiens” (Martin et al. 1141). However, these conclusions are reputed by Argue et al., who examined various cranial abnormalities in dozens of hominid fossil skulls. According to Argue: “Cranial and postcranial analyses of LB1 suggest that this skeleton is unlikely to be a microcephalic H. sapiens; the only similarity it shows to this morphology is a small endocranial volume” (Argue et al. 373). Argue goes on to say that, “LB1 is short in stature; it has a small cranial capacity that nevertheless is suggested to be neurologically complex. This combination of cranial and postcranial traits is unique, and we support the attribution by Brown and colleagues (2004) of LB1 to a new species” (373). The fact that so many anthropologists disagree when discussing the Flores fossils shows the wide range of scientific conclusions one can come up with depending on how extensive the examination of the fossils are.

After all the evidence presented, the question of whether or not to add a new species to our human lineage remains unanswered. The mounting evidence for a new species is backed up by the findings of Argue et al. and her comparisons of the Flores skull and limb bones to other fossils with similar abnormalities. Conversely, if one were going to put the H. floresiensis fossils on a new branch of the family tree, then why ignore the other fossils with comparable defects; adding them as a new species would make just as much sense as adding H. floresiensis. The answer may be as simple as our desire to know more about our past and how we became who we are. Human beings’ capacity for learning is unequalled in the animal kingdom, and it is through our past that we gain our future. As a culture, we far-exceeded any other species, and we continue to expand our abilities through knowledge of where we came from. Once we fully understand everything we need to know, new questions will appear for those who live long after we are gone, and it will then be their turn to debate what defines one species from another. Until then, to randomly assign a new species to an existing genus without an adequate amount of evidence is haphazard of a scientific community expected to thoroughly analyze all the data they can find before making such extreme claims.

Jones, S., Martin, R., Pilbeam, D., The Cambridge Encyclopedia of Human Evolution,
Cambridge University Press, 1992
Van Den Bergh, G.D., et al., The youngest Stegodon remains in Southeast Asia from the
Late Pleistocene archaeological site Liang Bua, Indonesia, Quaternary International
(2007), doi:10.1016/j.quaint.2007.02.001
Cela-Conde, C., Ayala, F., Genera of the Human Lineage, Proceedings of the National
Academy of Sciences of the United States of America, Vol. 100, No. 13, 2003, pp.
Bower, B., Evolution’s Mystery Woman, Science News, Vol. 170, 2006, pp. 330-332
Martin, R.D., Maclarnon, A.M., Phillips, J.L., Dobyns, W.B., Flores Hominid: New
Species or Microcephalic Dwarf?, The Anatomical Record Part A, Vol. 228A,
2006, pp. 1123-1145
Argue, D., Donlon, D., Groves, C., Wright, R., Homo floresiensis: Microcephalic,
pygmoid, Australopithecus, or Homo?, Journal of Human Evolution, Vol. 51,
2006, pp. 360-374