I guess the results here would surprise you if you assumed that hiring bias was primarily the result of an explicit bias against {gender, race, etc.}. While there is certainly this class of bias, I personally haven't found as much of it in the technology field as there is purported to be in general society.
What I have found, instead, is a more subtle bias that goes something like this: "I view myself (or that guy over there) as the model employee. I'm looking for someone who thinks and acts like we do -- not just on our level, but views problems the same way, is likely to arrive at the same solutions, has the same energy level, etc.". I believe this attitude forms the fundamental underpinning of both company culture and hiring bias. I've seen it work successfully over the short term (particularly in startups where you're trying to build a small team of really smart people that can build something quickly), but I think it is counter-productive over the longer term.
When I'm hiring, I simultaneously try to answer three questions: (1) Is this person capable of doing the job I'm hiring them for? (or grow into being capable), (2) Is this someone I could work with and who could work with my team?, and (3) What unique life experiences or perspectives does this person have that they could bring to the team and improve our culture or decision making?
What I've found is that some folks over-focus on (1) and sometimes (2) without adequately recognizing the value of (3). I personally believe that you don't remove bias by trying to legislate against it - you remove it by getting people to desire the alternative - diversity.