I would argue that earth is a sample of 1, and there are two interpretations of this:
a) N=1 is not an experiment; reject the sample.
b) Use the data you have, however rotten. Then 100% of earth-like planets are... like the earth. Hence, most or all earth-like planets shall be like us too.
Is there a name given to alien intervention -- the idea that humans were introduced here for observation or long-term harvesting?
X-fileia.
I guess what I need to say is that there is absolutely no evidence whatsoever of "alien" influence of life on earth, no evidence whatsoever that aliens even exist, and no evidence whatsoever that there are alien worlds that harbor life of any sort.
Panspermia = no evidence whatsoever.