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The Secrets of DNA In Ancient Bones

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#1 Dr. Joseph Lorenzo

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Posted 12 August 2015 - 02:11 PM

While members of the ASBMR generally study bones to learn about the function of their cells or the ways in which their structure and mechanical properties are altered in health and disease, paleontologists and archeologists study fossilized bones to glean information about ancient animals and humans. Until thirty-five years ago, knowledge about ancient species was limited to what could be obtained from the morphology of their bones or the location where the specimens were found. However, advancements in molecular biology and, especially, in DNA sequencing have revolutionized the amount of information that ancient bones can yield.

This is highlighted in a series of recent articles in the journal Science (1). The field started in the early 1980’s with PCR cloning of DNA from samples but has progressed in the modern era to high throughput Next-Gen sequencing. Today, vast amounts of information can be obtained about the similarities and differences between present day and ancient plants, animals and humans. To generate this information, scientists have perfected techniques to isolate DNA from ancient specimens and identify the degree to which the ancient DNA was contaminated by DNA from modern species. This has been accomplished with spectacular success within the limitations of the stability of DNA in fossils. So far, the oldest DNA that has been reliably sequenced is from a 700,000-year old horse. DNA from older specimens is too degraded to be of any use, which precludes studies of dinosaur fossils, since these existed from 250 to 66 million years ago.

Perhaps the most important information obtained from studies of the DNA in ancient bones is the degree to which modern humans differ from extinct human species. It has now been established that modern Europeans and Asians have inherited 1% to 3% of their DNA from Neandertals and up to 5% from the related Denisovan species of ancient humans (2). This means that interbreeding among these somewhat divergent groups occurred in the past. A recent study examining the length of the Neandertal sequences in a jaw bone specimen from an ancient human who died 37,000 to 42,000 years ago identified several segments of Neandertal DNA sequence (some more than 50 million base pairs in length) in the specimen that otherwise was predominantly (89 to 95%) modern human DNA. This finding implies that an ancestor of the man whose jawbone the DNA was extracted from had an ancestor who mated with a Neandertal within four to six generations of his birth (less than 200 years).

Next-Gen sequencing is also allowing more precise mapping of the migration of the ancestors of native North and South Americans from Asia and the relationships between Native Americans and the native peoples of Australia and Melanesia (a group of islands northeast of Australia) (3).

Most fascinating may be studies of the function of Neandertal DNA sequences that are preserved in the modern human genome. It has been suggested that these are preserved because they impart an evolutionary advantage that allowed modern humans to make a significant leap in their adaption to hostile environments as they migrated from central Africa throughout the world (4).

The technology of Next-Gen DNA sequencing is rapidly evolving. As it becomes less expensive and more available, it should allow us to understand even more secrets of our evolution and the nature of our ancient ancestors.

Joe Lorenzo

Farmington, CT, USA

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