How much do grades in non-major subjects matter?

<p>Hi,
I will be returning back as a Junior in college this fall. I am a biology major and plan to pursue graduate school for my PhD (have not decided specific field in Biology though). I was wondering how much grades from non major fields like humanities would matter during the process of application and how much they are weighed in? I am also curious because when I was applying for one research internship for this summer, one of them in particular specified that in required a lor from a non-science faculty which got me wondering if it were indicative of anything?
Thank you</p>