User:Horbaly.5/sandbox

CONTRIBUTION TO HOMO FLORESIENSIS PAGE STARTS HERE Link: https://en.wikipedia.org/wiki/Homo_floresiensis

I added the following to the 'Hypotheses of origin' section to explain the importance of the current debate

The proper classification of hominin remains is imperative to understanding the course of human evolution. Previous discoveries of hominin fossils, such as the Neandertals and Pithecanthropus erectus, have sparked similar debates among the scientific community, usually challenging the accepted paradigm of human evolution and taxonomic status of our predecessors. In addition to the evolutionary implications of understanding the phylogenetic progression of humans, the International Code of Zoological Nomenclature prohibits developmentally abnormal individuals from being classified as a separate species. Because of this rule, should pathology explain the appearance of the skeletal remains, then the name ‘Homo floresiensis’ would be nullified and the skeletons would be classified as Homo sapiens. If the remains are representative of a new species, Homo floresiensis creates a drastic paradigm shift in our understanding of the human history of divergence, meaning that the genus Homo is “morphologically more varied and flexible in its adaptive responses than previously thought”.

I contributed the following to the Laron syndrome hypothesis

This IGF-I deficiency is commonly caused by an exon deletion, and produces two distinct phenotypic changes in the skeleton: short stature and a small skull, which also happen to define the phenotype of H. floresiensis. They compared the cranial and postcranial skeleton of LB1 with those of 64 Laron syndrome patients. The cohort of Laron syndrome patients exhibited statures ranging from 95 to 136 cm in adult females, and 116 to 142 cm in adult males. The estimated height for the LB1 remains places it at the lowest end of the female range. The extremely small endocranial volume of LB1 is actually smaller than anything exhibited in Laron syndrome patients. Despite this inconsistency in brain size, Hershkovitz et al. still assert there are enough characteristics shared between LB1 and the Laron syndrome patients to suggest this pathology explains the skeletal appearance.

I created a new section called 'Insular dwarfism hypothesis' to explain the views of the original discoverers of the LB1 remains

The original report further claims neither growth retardation nor pituitary dwarfism could be responsible for the unique skull and short stature (however, no reason is provided); instead, Brown et al. suggest insular dwarfing of H. erectus as a result of selective pressures acting on island populations. This theory posits that the tropical rainforests present on the island tend to be a calorically impoverished environment, causing a dietary strain on hominins, especially in the absence of agriculture. Because of reduced resources, an advantage is placed on individuals who are smaller with lower energy requirements. This selection can also greatly affect sensory organs such as the brain, which could explain the small endocranial volume present in H. floresiensis.

FINAL DRAFT STARTS HERE - Is Homo floresiensis a unique species?

Ever since nine unique partial hominin skeletons were discovered on the island of Flores in 2003, anthropologists have debated where exactly these remains fall in the human phylogenetic tree. Original discoverers and researchers posit that the skeletons represent a new and distinct species of human (Morwood, 2004; Brown, 2004), while others suggest they are pathological specimens of early Homo sapiens (Hershkovitz et al., 2011; Henneberg et al., 2014). There is a consensus that the remains are hominin in origin, meaning they belong to the taxonomic tribe that includes recent humans and extinct ancestral and related forms. Most of the remains were found in levels of the Liang Bua cave which dated back to between 18,000 and 16,000 thousand y B.P. (note that Homo sapiens first appeared ~55-35 y B.P.); only one set of remains, LB1, includes a skull (Aiello, 2010). What is most puzzling to anthropologists and scientists is the small body size exhibited by the skeletons—they are estimated to be about 1 m (3.3 ft) in height with LB1’s endocranial volume estimated to be 380 cm3 (Brown, 2004). While the size alone is enough for some scientists to deem them a separate species, critics claiming pathology suggest developmental disorders such as Laron syndrome and Down syndrome (Aiello, 2010). From an outsider’s perspective, the fact that this tiny sample was given its own scientific name, Homo floresiensis, might suggest a consensus on declaring it a new species of human, but in reality, the debate is far from over.

The proper classification of hominin remains is imperative to understanding the course of human evolution. Previous discoveries of hominin fossils, such as the Neandertals and Pithecanthropus erectus, have sparked similar debates among the scientific community, usually challenging the accepted paradigm of human evolution and taxonomic status of our predecessors. In addition to the evolutionary implications of understanding the phylogenetic progression of humans, the International Code of Zoological Nomenclature prohibits developmentally abnormal individuals from being classified as a separate species (Ride, 1999). Because of this rule, should pathology explain the appearance of the skeletal remains, then the name ‘Homo floresiensis’ would be nullified and the skeletons would be classified as Homo sapiens. If the remains are representative of a new species, Homo floresiensis creates a drastic paradigm shift in our understanding of the human history of divergence, meaning that the genus Homo is “morphologically more varied and flexible in its adaptive responses than previously thought” (Brown, 2004).

Laron syndrome is one of the leading explanations of H. floresiensis as a pathological modern human. Laron syndrome was first defined in 1966 as an inbred congenital defect of a growth hormone receptor which creates a deficiency in IGF-I, a growth factor that acts like insulin (Laron, 1966). This IGF-I deficiency is commonly caused by an exon deletion, and produces two distinct phenotypic changes in the skeleton: short stature and a small skull, which also happen to define the phenotype of H. floresiensis. In 2007 a team of scientists, including Laron himself, compared the cranial and postcranial skeleton of LB1 with those of 64 Laron syndrome patients (Hershkovitz, 2007). The cohort of Laron syndrome patients exhibited statures ranging from 95 to 136 cm in adult females, and 116 to 142 cm in adult males. The estimated height for the LB1 remains is 106 cm, which places it at the lowest end of the female range. The extremely small endocranial volume of LB1 (380 cm3) is actually smaller than anything exhibited in Laron syndrome patients. Despite this inconsistency in brain size, Hershkovitz et al. still assert there are enough characteristics shared between LB1 and the Laron syndrome patients to suggest this pathology explains the skeletal appearance. Additional features of LB1—short and slightly prognathic face, absent/underdeveloped frontal sinuses, and congenital absence of the third molar—are consistently exhibited in patients exhibiting other growth hormone deficiencies (Hershkovitz, 2007).

Critics of a pathological explanation for H. floresiensis claim the ‘new species’ hypothesis put forth by original researchers (Brown, 2004; Morwood, 2004) cannot be rejected because no medical diagnosis has fully accounted for why these supposed pathological traits so closely mimic ancestral humans (Aiello, 2010). Others have also identified skeletal similarities between H. floresiensis and its hominin predecessors Homo erectus and Australopithecus afarensis. The cranial shape and vault thickness of LB1 is seemingly consistent with that of H. erectus, while the endocranial volume is consistent with minimum measures recorded for Australopithecus, and therefore well below the accepted range for the genus Homo (Brown, 2004). This mosaic of derived traits alongside primitive traits is also cited as being indicative of a new species, however it should be noted that similar patterns show up in teratological (developmentally abnormal) patients (Henneberg et al., 2014).

The original report further claims neither growth retardation nor pituitary dwarfism could be responsible for the unique skull and short stature (however, no reason is provided); instead, Brown et al. suggest insular dwarfing of H. erectus as a result of selective pressures acting on island populations. This theory posits that the tropical rainforests present on the island tend to be a calorically impoverished environment, causing a dietary strain on hominins, especially in the absence of agriculture. Because of reduced resources, an advantage is placed on individuals who are smaller with lower energy requirements (Lomolino, 1985). This selection can also greatly affect sensory organs such as the brain, which could explain the small endocranial volume present in H. floresiensis.

The most recent proposed explanation for Homo floresiensis suggests that the individuals were early modern humans with Down syndrome. The researchers behind this hypothesis claim that the occipitofrontal circumference of LB1 (reported for the first time in this study) and the craniofacial asymmetry make it consistent with clinical records of patients with developmental disorders (Henneberg et al., 2014). In response to the proponents of a new species, Henneberg’s team made the important distinction that the characteristics identified as traits suggesting a discrete species were not present in the remaining eight skeletons in the sample. Thus, the distinct species hypothesis hinges predominantly on the LB1 skull, a sample size of one.

Initially, Henneberg et al. were not intending to make a specific diagnosis on LB1, but simply provide proof of a developmentally abnormal Homo sapiens. However, Down syndrome became a logical explanation after observing various traits which were consistent with a high proportion (>10%) of Down syndrome patients. Down syndrome is one of the most common human developmental disorders, occurring in approximately 1 of every 700 births, and has also been found in related hominoids, such as orangutans and chimpanzees (Henneberg et al., 2014). About 80 signs have been identified as indicators of the syndrome, and each indicator can fall on a spectrum of varying expression (Dietz et al., 2011). Craniofacial asymmetry is one of these signs, and is present in LB1 in the form of palatal rotation that exceeds a normal range. While other researchers have attributed the asymmetry to postmortem taphonomic alterations, Henneberg considers this an impossibility since corresponding asymmetry is present in the tooth wear pattern which developed in life as a result of the palatal rotation.

Occipitofrontal circumference (OFC) was also analyzed in this study. Microcephaly, a sign of Down syndrome, is defined as an OFC that is 2 or more standard deviations below the normal population (Henneberg et al., 2014). The OFC consistently observed for the LB1 skull (385 mm) was compared to the average OFC for the modern Rampasasa people (450 – 522 mm), a comparable population living near the Liang Bua cave. The average OFC of human skeletons recovered nearby in Palau (441 – 502 mm) was also used for comparison. In relationship to the normal Rampasasa and Palau ranges, the OFC of LB1 falls between –3.17 to –6.68 SDs, and between –2.73 and –5.71 SDs, respectively (Henneberg et al., 2014). Therefore LB1, by definition, fits the microcephaly specifications of Down syndrome.

As with most species, many evolutionary paths are possible, however some are more probable than others. Based on the research presented in the years since its discovery, the most parsimonious explanation for the physical appearance of H. floresiensis seems to be those which suggest pathology. This is the most logical explanation because it relies on quicker-acting evolutionary forces, such as the exon deletion and inbred congenital defects that cause Laron syndrome. In regards to the opposing argument, accepting H. floresiensis as a new species would cause shifts in a previously held paradigm concerning the genus Homo. While paradigm shifts can be a crucial part of defining species and creating a functional phylogenetic tree, the traits defined as ‘unique’ in H. floresiensis would conceivably be the result of thousands of years of evolution, yet no intermediate or similar specimens have been discovered. Furthermore, within the small sample that has been found, only the LB1 remains exhibit the traits scientists claim are evidence of a discrete species (Henneberg et al., 2014). This means that the new taxa H. floresiensis is inferred from one (incomplete) skeleton.

While pathology seems to be the most parsimonious explanation based on LB1, implications for the sample as a whole should be considered. The fact that nine sets of remains were found together—and with tools and artifacts representative of H. sapiens (Hershkovitz, 2007)—suggests little to no reduction in cognitive ability which might be present in the case of a developmental pathology. The capability of the H. floresiensis specimens to have grouped themselves together in life suggests they had a reflexive understanding of what made them different from other humans with whom they coexisted (such as Homo neanderthalensis and Homo sapiens). Should another individual or small population sample be discovered elsewhere, enough information may be gleaned to truly decide whether Homo floresiensis was appropriately defined as a new species, but until a new discovery is made there is not enough evidence to definitively settle on one hypothesis.

References

Aiello, L. 2010. Five years of Homo floresiensis. American Journal of Physical Anthropology 142(2): 167-179.

Brown, P., et al. 2004. A new small-bodied hominin from the Late Pleistocene of Flores, Indonesia. Nature 431: 1055-1061.

Dietz S.L., Blazek J.D., Solzak J.P., Roper R.J. 2011. Down syndrome: A complex and interactive genetic disorder. Genetics and Etiology of Down Syndrome: 65–96.

Henneberg, M., Eckhardt, R., Chavanaves, S., & Hsu, K. 2014. Evolved developmental homeostasis disturbed in LB1 from Flores, Indonesia, denotes Down syndrome and not diagnostic traits of the invalid species Homo floresiensis. Proceedings of the National Academy of Sciences 111(33): 11967-11972.

Hershkovitz, I., Kornreich, L., & Laron, Z. 2011. Comparative skeletal features between Homo floresiensis and patients with primary growth hormone insensitivity (Laron syndrome). American Journal of Physical Anthropology 134(2): 282-289.

Lomolino, M.V. 1985. Body size of mammals on islands: The island rule re-examined. The American Naturalist 125: 310-316.

Morwood, M.J., et al. 2004. Archaeology and age of a new hominin from Flores in eastern Indonesia. Nature 431: 1087-1091.

Ride, W.D.L. 1999. International Code of Zoological Nomenclature (International Trust for Zoological Nomenclature, Oxford, UK).

Oct. 1 Article Edits

https://en.wikipedia.org/wiki/Homo_floresiensis

3 comments for improvement: This page goes into strong detail about many of the proposed hypotheses for the origin of H. floresiensis, but the 'Down syndrome hypothesis' section is a little neglected (likely due to the recentness of the proposal). For now, I have three suggested areas of improvement:

1. More details should be included about the specific physical attributes which led researchers to believe Down syndrome was the pathology at work (i.e. facial asymmetry, endocranial volume, brachycephaly, flat feet)

2. It also might be important to include that the researchers found previous published measurements regarding stature and endocranial volume were biased downward; their corrected measurements actually put Down syndrome within the realm of possibility.

3. Also to be discussed is the fact that the projected statures of LB1 and other associated specimens are within the normal ranges for this region, though indeed at the low end. On the other hand, the endocranial capacity of LB1 is several standard deviations below the norm.

One sentence with citation: Down syndrome is one of the most common human developmental disorders, and is also exhibited in related hominoids such as the orangutan and the chimpanzee.

Is Homo floresiensis a distinct species? Annotated Bibliography

Brown, P., & Maeda, T. (2009). Lian Bua Homo floresiensis mandibles and mandibular teeth: A contribution to the comparative morphology of a new hominin species. Journal of Human Evolution, 57, 571-596. Retrieved September 14, 2014, from http://www.sciencedirect.com/

This article will be valuable for my research project because it represents research that supports the claim that Homo floresiensis is a distinct species. It will allow me to contribute greatly to the Wikipedia page on Homo floresiensis because it provides in-depth discussion about this hominin’s dental morphology, an aspect greatly lacking in the Wikipedia page.

Obendorf, P., Oxnard, C., & Kefford, B. (2008). Are the small human-like fossils found on Flores human endemic cretins? Proceedings of the Royal Society: Biological Sciences,275, 1287-1296. Retrieved September 14, 2014, from http://rspb.royalsocietypublishing.org/

This article supports the claim that Homo floresiensis is not a distinct species. Rather, the authors’ research suggests that they are Homo sapiens suffering from cretinism among a largely unaffected population of biologically ‘normal’ humans. This theory is briefly mentioned on the Wikipedia page, and much information could be contributed to that section.

Hershkovitz, I., Kornreich, L., & Laron, Z. (2011). Comparative Skeletal Features Between Homo Floresiensis and Patients with Primary Growth Hormone Insensitivity (Laron Syndrome). American Journal of Physical Anthropology, 134(2), 282-289.

This article discusses the possibility that the small stature of H. floresiensis can be attributed from Laron Syndrome. This article goes into great detail about how Laron Syndrome produces small cranial morphology, and other phenotypic alterations that are consistent with those witnessed in the H. floresiensis remains. This hypothesis is mentioned on Wikipedia, but the information is sparse.

Henneberg, M., Eckhardt, R., Chavanaves, S., & Hsu, K. (2014). Evolved developmental homeostasis disturbed in LB1 from Flores, Indonesia, denotes Down syndrome and not diagnostic traits of the invalid species Homo floresiensis. Proceedings of the National Academy of Sciences, 111(33), 11967–11972-11967–11972. Retrieved September 14, 2014, from http://www.pnas.org/content/111/33/11967.full.pdf html

This is an extremely recent article which suggests H. floresiensis suffered from Down syndrome. The authors compared the cranial morphology and capacity to human patients past and present who suffered from Down syndrome and have discovered striking developmental similarities. This hypothesis deems the title of H. floresiensis unnecessary. Since this research has only recently been brought forth, the related information on Wikipedia is virtually non-existent.

Aiello, L. (2010). Five years of Homo floresiensis. American Journal of Physical Anthropology, 142(2), 167-179.

This article addresses many of the suggested hypotheses about Homo floresiensis, and simultaneously presents a different hypothesis: that H. floresiensis is a late-surviving ancestor of early Homo. This suggests it is not its own species, as so many of the other hypotheses insist. Though it requires a bit of a paradigm shift, this hypotheses might be the most logical. The Wikipedia section on this hypothesis is currently very brief.