The Catalysts Behind Google's Evolution
Google's approach to quality search is, at best, reactive. Updates in algorithms wouldn't have been possible without catalysts. Google's legal tussle with Search King in 2003 is just one of many (where Google won). Below are some search engine feature updates and the reason for their immediate implementation.
Nofollow enables websites to instruct search engines not to follow any links. Google created this feature in response to the vulnerability of online comments to links; something like a back door for excessive linking, which is now frowned upon. When link spamming refused to stop, Google webspam guru Matt Cutts required nofollow for PageRank-compliant links.
One of the longest developments, automatic filters have engaged in numerous tugs-of-war with black-hat practices for a long time. It started out as flagging keyword-heavy content as spam, but merchants responded by buying ads. When Google launched a cleansing crusade against poor content, high-authority websites capitalised on their reputation by releasing poor content.
The rationale behind the development of PageRank spans out to different catalysts. Aside from the legal tussle with Search King, there's link farming, sponsoring widgets, and buying expired domains. These practices mean penalties today because they reciprocate or create low-quality content for users.