According to a new study, the oils that are developed from mustard and horseradish were produced millions of years ago. As per the University of Missouri, plants produce these oils to defend against hungry insects.

According to Chris Pires, an MU Bond Life Sciences Center researcher and associate professor of biological sciences in the College of Arts and Sciences, "We found the genetic evidence for an arms race between plants like mustards, cabbage and broccoli and insects like cabbage butterflies. These plants duplicated their genome and those multiple copies of genes evolved new traits like these chemical defenses". Pires added that later cabbage butterflies responded by developing new ways to fight against them.

Compounds called glucosinolates produce the "zing" in mustard, and caterpillars can't stand this flavour unlike humans. Brassicales, an order of plants in the mustard family, had first developed this defense during the time when dinosaur went extinct. Soon after that it diversified to produce over 120 types of glucosinolates.

According to Hanna Heidel-Fischer, a lead author on the study based at the Max Plank Institute for Chemical Ecology in Germany, the difference in the detoxification mechanisms among species and their gene copies revealed about important evolutionary changes.

A team of researchers observed 9 existing Brassicales genomes and also generated transcriptomes, the set of all RNA in a cell, in order to make their findings. Using this method, the researchers created a map of the evolutionary family tree of these species to find out when specific changes took place.