Even pre-human ancestors cried while cutting onions

Washington, Mar 20 : The body sensors that bring tears in your eyes when you're cutting onions have been around for 500 million years, says a new study.

According to a report by Brandeis University scientists in Nature, whenever a person chokes on acrid cigarette smoke or feels like he/she is burning up from a mouthful of wasabi-laced sushi, the response is triggered by a primordial chemical sensor conserved across some 500 million years of animal evolution.

Such substances contain tissue-damaging and irritating chemicals. When you get a taste or waft of them, a protein found throughout your body is thought to sense these irritating chemicals and send signals to your nervous system. The result is pain, which results in the tears, reports Live Science.

In the new study, chemical-sensing protein, called TRAPA1, was found in flies. And, according to the boffins, the protein could date back millions of years to the common ancestor of all the varied creatures in the animal kingdom.

"While many aspects of other chemical senses like taste and smell have been independently invented multiple times over the course of animal evolution, the chemical sense that detects these reactive compounds is different," said study author Paul Garrity, a biologist at Brandeis University in Waltham, Mass. "It uses a detector we have inherited in largely unaltered form from an organism that lived a half-billion years ago, an organism that is not only our ancestor, but the ancestor of every vertebrate and invertebrate alive today."

Using a variety of bioinformatic methods (bioinformactics applies computer programs and statistic techniques to study biological data), Garrity and his colleagues reconstructed TRPA1''s family tree back some 700 million years.

They then used several computer programs to figure out how the proteins would relate to each other in terms of evolution.

"We discovered that a new branch split off the tree at least 500 million years ago, and that this new branch, the TRPA1 branch, appeared to have had all the features needed for chemical sensing even back then," Garrity said. "Since that time, it appears that most animals, including humans, have maintained this same ancient system for detecting reactive chemicals."