Did UV rays spell doom for Neanderthals?

The extinction of Neanderthals and large mammals 40,000 years ago coincided with a weakened geomagnetic field that reduced protection from ultra-violet radiation, a new study shows. 

“This tells us more about how our ancestors evolved within the mammal population,” said University of Florida geological sciences professor James Channell. “Ultra-violet radiation was an important influence on mammal evolution.”
 
Unlike Neanderthals, modern humans survived the prolonged UV radiation due to a key difference in their genome that better defended them from UVR. Scientists already knew that a protein called the aryl hydrocarbon receptor differed in Cro-Magnon and Neanderthals, but theorized the variation made Neanderthals more susceptible to environmental toxins such as those from cooking fires. Channell’s study — done with Luigi Vigliotti of the Italian National Research Council’s Institute of Marine Sciences — associates the different variants of AhR in Neanderthals and modern humans with different tolerance to UVR and correlates Neanderthal decline to weakened magnetic field and resulting UVR exposure.

Over generations, magnetic fields can spell the difference between extinction and survival: When the field is strong, it shields the Earth from solar wind that generate ozone-depleting chemicals, which weaken the ozone layer and allow more UV radiation to reach Earth’s surface. Scientists can track magnetic field strength through time by sampling sea-floor sediments and ice cores.
 
During the last approximately 100,000 years, several episodes of low field strength — hence more intense UV radiation — affected large long-lived mammals, including Neanderthals, whereas smaller mammals were often able to cope. The timing of extinction was dependent on global magnetic field strength, the impacted locations (Australia, North America and Europe) on the geometry of atmospheric ozone depletion.
 
“The effect was not a blitzkrieg, but a process that affected the genome over time,” Channell said.
 
Channell and Vigliotti’s study was published in the journal Reviews of Geophysics on May 29. Building on our understanding of fluctuating magnetic fields and their impact could unlock more secrets from pre-history.
 
“We need to know more about magnetic field strength in the past, how UVR affects the genome of mammals, and improve the chronology of mammal extinction,” Channell said.