Go study the links I provided. It is all backed with research & empirical data.
The research shows that "evolution" is not a gradual thing nor is it strictly vertical. There have been enough fly-bys, landings & telescopic analysis to show that other bodies in this system have a high likelihood of some form of biological life upon them. It also shows that extraterrestrial impacted material carries biological substances. There is enough inter-disciplinary study to theorize & substantiate that this planet was seeded by life from elsewhere.