If relating Dawin's theories to external areas such as politics or sports, then Darwin's theories could be seen as very conservative. It basically translates into the environment picking winners and losers based on performance, and avoiding any control by some external force not included in that environment (government interfering with trade) However, in relation to nature, his theories are very liberal with his extensions of facts and assumptions that must be made to support his argument
I would say that I don't think that Darwin's ideas are liberal or conservative. I would say that it is just science. However, if I had to pick I would say that they are liberal not because they are, but because more liberals agree with his thoughts than conservatives do.
Darwin's theories tend to be considered a liberal point of view because they are offered in counter to the typical religions beliefs about creationism. Without getting into which one is right or pigeon holing them with certain stigmas, it is probably true that Darwin's emphasis on science and evolution is important.
I definitely think that Darwin's theories are liberal. There is a lot of correlation between liberal tendencies and the support of theories that Darwin advocates. I do think though that some people who are conservative can agree with some of Darwin's theories regardless. I just think more people who agree with Darwin tend to be liberal.
Darwin theorizes about evolution, which is a part of biological science. While his theories have been politicized, especially in American, I do not believe they are inherently liberal or conservative. His theories and studies are based in observable fact and they have nothing to do with politics at all. It is important to distinguish the difference. Darwin didn't ask to start a political war on his findings.