Earth is in that unique sweet spot formed by the crest of several periodic NRG waves that reverberate through-out the walls of the universe. Prior to the existence of any sentient life forms within the universe, with each passing wave, the complex thought patterns of earthly life carried across the galaxy and unto the remainder of the universe. As other biospheres became overwhelmed by these waves of "quantum memes" they changed; their lifeforms forced to adjust behavior in harmony with the onslaught of the new thoughts or eventually perish.
It's the inevitable conclusion that the universe was usurped by human-kind. As the story goes, Earth became the home of the universe's first sentient life forms - hominids. When the next cresting passed through Earth some 30,000 years ago; the drug-induced lucid dream of a particular hominid mystic became the standard of thought which bounced through the remainder of the universe. That quantum meme spread through the galaxy and altered choices by those other life forms affecting mate selection, danger avoidance, and the entire range of normal behavior to include facets of that First Thought. As those life forms accelerated into sentience, they became familiar with human thought and so became human at least in the sense of behavior. In many cases, as a result of mate selection, many of those life-forms chose aesthetic proportions - where possible - common to humans. In a way, the First Though encouraged human-like features to appear in these alien species.