Google keeps expanding. After releasing Buzz, it’s reaching deeper into social networking by buying Mechanical Zoo Inc., which operates a free question-and-answer web service called Aardvark. Founded by ex-Googlers in 2007, the San Francisco-based company claims Aardvark is the first social search engine, organized more by the wisdom of crowds than by a whizzy search algorithm.

At a reported cost of $50 million, this is pocket change for Google, which reported $6.67 billion in revenue for Q4 of 2009. Still, the acquisition may yet require significant investment. Aardvark has accumulated only about 90,000 users since it launched in 2009, and only 55.9% of them have ever asked a question.

Here’s how it works: you ask Aardvark a question like, say, “how do I make tiramisu?” which is then sent to an army of knowledgeable helpers who have registered with Aardvark – some may be friends already in your social network; others well-informed strangers. Scale is key here. With Google’s help, the number of quality responses increases as more “experts” join up.

Google hasn’t given a lot of detail about how Aardvark may be implemented into its new Buzz social media strategy, if at all, nor if there’s a place for Aardvark’s expert-vetting service for Google’s enterprise push.

All in all, though, a smart move on the search giant’s part. While there’s no doubt that Google’s algorithms got it to where it is today, now it’s adding a human face to the search.