1.8 million years old fossil suggests only one human ancestor species, not three
Subodh Varma, TNN | Oct 18, 2013, 12.09 PM IST
This
2005 photo provided by the journal Science shows a 1.8 million-year-old
pre-human skull found in the ground at the medieval village Dmanisi,
Georgia. It's the most complete ancient hominid skull found to date, and
it is the earliest evidence of human ancestors moving out of Africa and
spreading north to the rest of the world, according to a study
published on Thursday. (AP Photo)
RELATED
NEW DELHI: A bunch of skulls of human ancestors
dating back to 1.8 million years ago has created a storm among
scientists. The discovery suggests that three human ancestor species
were actually just one, with variations in features.
Five hominid skulls were found by scientists in Dmanisi, Georgia in 2005. The site is well-known for having revealed a range of fossils. Of the five skulls, one was found to fit with a jaw bone found in 2000 at the same site. This fitting together gave rise to a complete skull.
Informally known as "skull 5", it "is the most complete skull of an adult from this date", says Marcia Ponce de Leon, of the Anthropological Institute and Museum in Zurich, Switzerland, and one of the authors of the study.
Scientists who discovered the five skulls were amazed to find that there were wide structural differences between them. The differences were so prominent that in normal course they would led the scientists to call them of different hominid species.
"(W)e know that these individuals came from the same location and the same geological time, so they could, in principle, represent a single population of a single species," says co-author Christoph Zollikofer, a neurobiologist at the same institute as Ponce de Leon, quoted in the scientific journal Nature. All of the skulls excavated so far were probably deposited within a 20,000-year time period, he notes.
The three human ancestor species that have been described till date are Homo habilis, Homo rudolfensis and Homo erectus. Fossil remains having different features led to this classification. Ut the Georgian fossils have features which are scrambled up. For instance, the volume of skull 5's braincase is only 546 cubic centimeters, about one-third that of modern humans. Yet, the hominin's face was relatively large and protruded more than the faces of the other four skulls found at the site. Skull 5 has just 75 percent of brain volume compared to a larger skull found there.
Statistical analysis of skull sizes appears to have supported the scientists claim that the skulls belong to the same species, Homo erectus. Variation in skull size is similar to the variation in skull sizes found among humans and chimpanzees, the scientists say.
Many scientists have expressed disagreement over the Georgian group's interpretation of the fossils. "Cramming the three species, which overall inhabited areas from Africa to Indonesia, under the H. erectus umbrella might not be scientifically justified," Nature quoted Fred Spoor, a palaeontologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany as saying.
Statistical analyses of general cranial shape are not necessarily good at discriminating between species, according to him. He recommended analysis of specific anatomical traits, such as height of the braincase or diameter of the eye socket. Such easily quantifiable characteristics are typically used to identify species and construct evolutionary family trees.
Five hominid skulls were found by scientists in Dmanisi, Georgia in 2005. The site is well-known for having revealed a range of fossils. Of the five skulls, one was found to fit with a jaw bone found in 2000 at the same site. This fitting together gave rise to a complete skull.
Informally known as "skull 5", it "is the most complete skull of an adult from this date", says Marcia Ponce de Leon, of the Anthropological Institute and Museum in Zurich, Switzerland, and one of the authors of the study.
Scientists who discovered the five skulls were amazed to find that there were wide structural differences between them. The differences were so prominent that in normal course they would led the scientists to call them of different hominid species.
"(W)e know that these individuals came from the same location and the same geological time, so they could, in principle, represent a single population of a single species," says co-author Christoph Zollikofer, a neurobiologist at the same institute as Ponce de Leon, quoted in the scientific journal Nature. All of the skulls excavated so far were probably deposited within a 20,000-year time period, he notes.
The three human ancestor species that have been described till date are Homo habilis, Homo rudolfensis and Homo erectus. Fossil remains having different features led to this classification. Ut the Georgian fossils have features which are scrambled up. For instance, the volume of skull 5's braincase is only 546 cubic centimeters, about one-third that of modern humans. Yet, the hominin's face was relatively large and protruded more than the faces of the other four skulls found at the site. Skull 5 has just 75 percent of brain volume compared to a larger skull found there.
Statistical analysis of skull sizes appears to have supported the scientists claim that the skulls belong to the same species, Homo erectus. Variation in skull size is similar to the variation in skull sizes found among humans and chimpanzees, the scientists say.
Many scientists have expressed disagreement over the Georgian group's interpretation of the fossils. "Cramming the three species, which overall inhabited areas from Africa to Indonesia, under the H. erectus umbrella might not be scientifically justified," Nature quoted Fred Spoor, a palaeontologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany as saying.
Statistical analyses of general cranial shape are not necessarily good at discriminating between species, according to him. He recommended analysis of specific anatomical traits, such as height of the braincase or diameter of the eye socket. Such easily quantifiable characteristics are typically used to identify species and construct evolutionary family trees.
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