Last night, 10 of the top Republican candidates for president battled it out on live TV, but according to a new study, it’s not just what they’re saying that swings votes—it’s also how they’re saying it. The study, published online today in PLOS ONE, shows that voters tend to favor candidates with deeper voices. People with low-pitched voices have higher testosterone levels, which also correlate to bulkier muscles and more aggressive behavior—attractive qualities in prehistoric leaders. Now, when deep-voiced politicians—including women—give a speech, scientists think it might strike a chord with remnants of our caveman selves, evoking an image of physical strength and competence. To investigate this idea, researchers ran a mock election. They played two recordings of male and female “candidates” that were digitally modified to make one higher pitched and one lower pitched. The researchers then asked “voters” which candidate was stronger, more competent, older, and—ultimately—would win their vote. Voters chose the low-voiced candidate for most questions, and a whopping 67% gave them their vote. But what does this mean for the leading candidates in last night’s debate? Donald Trump, for one, might not be leading in recent polls because of his off-the-charts testosterone levels and physical prowess, but because he knows how to pump up the bass.