By Paige Minteer
The evolution of humans is the result of a number of speciation events that have built upon one another to create the modern-day human species: Homo sapiens. Humans are believed to have evolved from a line of ancestors dating millions of years ago and originating in Africa. The subsequent Homo sapien ancestors dispersed across Europe and Asia. Of particular note are the "Homo denisova", of which fragments were found in Siberia, and Homo floresiensis, of which fragments have been found in Flores, Indonesia. Both of these species are of particular relevance to the Southeast Asian and Pacific Island areas because of their continued presence in the DNA of modern humans living there.
"Homo denisova" is considered to be a bridge species between the Neanderthal ancestors and the Homo sapiens species. They are said to have bred with modern humans, and potentially Neanderthals, producing hybrid people. "Homo denisova" are assumed to have had dark skin, brown eyes and brown hair. The teeth are larger than that of which Neanderthals and modern humans have, but more evidence is needed to further extrapolate the size and looks of this species (Hawks 2013). The only remnants of the "Homo denisova" species that have been found are a small toe bone fragment and two molars. This has been enough, however, to create a basic genomic sequence of the species. From this, genome researchers have traced gene markers to help determine the migration patterns of the species. By analyzing the gene flow of various generations of people in various areas in Eastern Europe, Asia and the South Pacific, researchers have been able to decipher the movement of the "Homo denisova". The origin of this species, however, is debated. While original estimates of the age of the bones make the species too old to be a shoot-off of the H. heidelbergensis species, some argue that it could be a very early speciation from this original species. Others believe "H. denisova" could bring to light a non-erectus evolutionary line. This differentiated evolutionary line would be a large branch-off compared to the branching depicted in current theories of human evolution.
Regardless of the ancestry of "H. denisova", the presence of this hominid has proved the evolution of humans in Asia to be far more complicated than originally believed.
"Homo denisova", however, is not the only intermediate Homo species in the modern human s ancestry. Homo floresiensis is another pre-modern human species common to the East Asia region. First discovered in Flores, Indonesia, H. floresiensis has been nicknamed the Hobbit species because of its small size. Scientists have found many near-whole skeletons of this species on the island.
This species is so closely related to the modern human that some scientists argue that they are merely a large group of dwarfs, not an entirely new species. The consensus, however, is that H. floresiensis is its own species. The small size is often accounted for by a phenomenon called island dwarfism. Used as an adaptation strategy when a species is confined to a small island with few resources for an extended period of time, the average size of individuals diminishes, causing the dwarfism seen in H. floresiensis. This adaptation strategy is mimicked by the pygmy elephants that are now extinct but may have been hunted by H. floresiensis (Natural History Museum 2010). However, some reject this island dwarfism theory based on the brain size of H. floresiensis. The brain of this species is about one third that of Homo erectus. Some assert, however, that typical cases of island dwarfism do not show brains shrinking at the same rate as the body. A third theory postulates that the Homo floresiensis is a pre-erectus hominid, or species that existed before the erectus family evolved, that speciated earlier than originally thought. Evidence from the skeletons supports this hypothesis, in that many features are closer to those of chimpanzees than of humans. The main problem with this hypothesis, however, is that there is no evidence for an intermediate species or this species on mainland Asia, proving no documentation for their transport to the island. While the exact ancestry and origin of Homo floresiensis is still up for debate, the existence of the species has contributed to the complex analysis of human evolution.
The theory of the diaspora of humans radiating away from their African homeland has been remolded and changed due to the discoveries of these newer forms of human ancestors. Homo floresiensis in particular exemplifies a divergent path from the original, linear idea of human evolution. While there is little certainty of the exact point of speciation, scientists postulate that this species evolved separately from other Homo erectus species because of their isolation on the island of Flores. Scientists are still debating how the original people arrived on the island, because it is many miles away from the nearest Asian mainland. While these people are thought to have used stone tools and perhaps fire, they are not believed to have built ships. In terms of migration, the story of "Homo denisova" is even more muddled. Scientists have used DNA analysis in order to try and determine the gene flow and therefore migration of the "Homo denisova" peoples. It is believed that these people migrated south from Russia towards South East Asia and met and bred with humans in their travels, creating a hybrid peoples (Harmon 2012). This information is based on the fact that many people of the South East Asian region share 5-6% of their DNA with Denisovan ancestors (Harmon 2012). It is believed that the people of mainland Asia do not contain the same amount of "H. denisova" DNA because subsequent waves of migrations hybridized the people and slowly replaced any trace of this DNA from the population. Specifically, "H. denisova" DNA is most prominently found in the people of Melanesia, New Guinea and South East Asia (Natural History Museum 2010). The "H. denisova" population is said to have been small and contained little genetic diversity. This persistence of the "H. denisova" DNA suggests that these ancient ancestors arent as removed from modern humans as might be assumed.
A discovery made in Palau in 2008 suggests that there may have been similar hobbit people on the Rock Islands. A researcher in Koror, Palau, Lee Berger, discovered some Sapien bones. While these bones have not been declared as specifically floresiensis or "denisova", they appear to be similar in size. Berger believes that these bones are humans that were subjected to island dwarfism. Other scientists claim the bones could simply belong to children. Bergers research suggests that the Palauan brains are double the size of the hobbit's brain. These bones demonstrate people who have enlarged teeth and smaller chins, which can be attributed to the island dwarfism process. These bones were found in caves on the rock islands, however these sites have been long known to tourists and many of the artifacts have been looted before researchers could thoroughly evaluate the findings. (Dalton). These findings have been evaluated and seem to support the island dwarfism theory more so than the delineation of floresiensis. (Culotta)
The evolution of the human species not only speaks to the past of the humans, but also to the future. The persistence of these ancestral human genes is still impacting human evolution today. "Homo denisova" and Homo floresiensis both remain somewhat of an enigma along the human evolutionary tree, but both of these species still provide useful insight into how humans have evolved. Finding these previously unknown species has complicated the story of human evolution, but has also made it a more complete tale.
"Homo denisova" and Homo floresiensis are of particular relevance to Asia and the South Pacific because they represent a non-Neanderthal, non-African line of evolution in this region of the world. These branching lines of evolution show the complicated, non-linear, nature of human evolution. Humans are complicated creatures and come from a complex ancestry, but it is through discoveries like remnants of "Homo denisova" and Homo floresiensis that the convoluted past becomes increasingly clear.
Author Bio: Paige Minteer is a sophomore in Environmental Studies at the University of Southern California.
Editors note: Scientific Research Diving at USC Dornsife is offered as part of an experiential summer program offered to undergraduate students of the USC Dana and David Dornsife College of Letters, Arts and Sciences through the Environmental Studies Program. This course takes place on location at the USC Wrigley Marine Science Center on Catalina Island and throughout Micronesia. Students investigate important environmental issues such as ecologically sustainable development, fisheries management, protected-area planning and assessment, and human health issues. During the course of the program, the student team will dive and collect data to support conservation and management strategies to protect the fragile coral reefs of Guam and Palau in Micronesia.
Instructors for the course include Jim Haw, Director of the Environmental Studies Program in USC Dornsife, Assistant Professor of Environmental Studies David Ginsburg, Lecturer Kristen Weiss, SCUBA instructor and volunteer in the USC Scientific Diving Program Tom Carr and USC Dive Safety Officer Gerry Smith of the USC Wrigley Institute for Environmental Studies.
Baab, Karen L. 2012. "Homo Floresiensis: Making Sense of the Small-Bodied Hominin Fossils from Flores." Nature.com. Nature Publishing Group, Web. 23 Mar. 2013. <http://www.nature.com/scitable/knowledge/library/homo-floresiensis-making-sense-of-the-small-91387735>.
Culotta, Elizabeth. "Hobbit Redux?" - ScienceNOW. Science, 11 Mar. 2008. Web. 14 June 2013.
Dalton, Rex. "Pacific "dwarf" Bones Cause Controversy." Nature.com. Nature Publishing Group, 10 Mar. 2008. Web. 14 June 2013.
"DNA of Ancient Siberian Human Uncovered." Natural History Museum. N.p., 25 Mar. 2010. Web. 23 Mar. 2013. <http://www.nhm.ac.uk/about-us/news/2010/march/dna-of-ancient-siberian-human-uncovered62927.html>.
Flatow, Ira. "Meet Your Ancient Relatives: The Denisovans." NPR. N.p., 31 Aug. 2012. Web. 20 Mar. 2013. <Meet Your Ancient Relatives: The Denisovans>.
Groves, Colin. "The Homo Floresiensis Controversy." HAYATI Journal of Biosciences. Dec. 2007. Web. 23 Mar. 2013. <http://journal.ipb.ac.id/index.php/hayati/article/view/252/118>.
Harmon, Katherine. "New DNA Analysis Shows Ancient Humans Interbred with Denisovans: Scientific American." New DNA Analysis Shows Ancient Humans Interbred with Denisovans: Scientific American. N.p., 30 Aug. 2012. Web. 23 Mar. 2013. <http://www.scientificamerican.com/article.cfm?id=denisovan-genome>.
Hawks, John. "Denisova." John Hawks Weblog. N.p., 20 Mar. 2013. Web. 23 Mar. 2013. <http://johnhawks.net/taxonomy/term/denisova>.
Stringer, Chris. "Ancient Denisovans and the Human Family Tree." Natural History Museum. N.p., 12 Jan. 2011. Web. 23 Mar. 2013. <http://www.nhm.ac.uk/about-us/news/2011/january/ancient-denisovans-and-the-human-family-tree93500.html>.
Tocheri, Matt. "Homo Floresiensis." Smithsonian National Museum of Natural History. N.p., n.d. Web. 23 Mar. 2013. <http://humanorigins.si.edu/evidence/human-fossils/species/homo-floresiensis>.
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