Up All Night in the Triassic

July/August 2017

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Most mammals, undergraduates included, are nocturnal. As the fossil record has borne out other similarities among species, scientists have long hypothesized that humans’ earliest mammalian ancestors would have favored the night too. Now a team led by professor of biology Liz Hadly has found direct genetic evidence in support of this hypothesis.    

The team tracked night vision genes across a set of mammals and reptiles. Drawing upon knowledge about the animals’ shared ancestry, the researchers deduced when these genes became enhanced to improve sight in low light. Because these genes became enhanced only after reptiles and mammals diverged in their lineage, about 200 million years ago, Hadly’s team concluded that the earliest common mammalian ancestor was likely active during the night.

Hadly is now planning more comprehensive studies such as figuring out whether an improvement in one sense led to a weakening in another. Diurnal animals, for example, probably compensated for their poor night vision in other ways.

“Sensing our environment is one of the most important things we do,” Hadly says. “If you are minimizing your ability to do well at night, are there other senses that are heightened still to avoid predation?”   

Results are pending, but one thing is clear: Habitual all-nighters are one more way to be attuned to the past.

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