So many solar systems out there, life evolved in many planets for sure. No proof but no doubt.
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There's still doubt:
https://en.wikipedia.org/wiki/Drake_equation#Range_of_result...
To prove, we would need to find such life.
To not have doubt, we need to have a reasonably high confidence that such life is there. However, the estimates are so wild and range from very unlikely to no-doubt. Thus, there is doubt (to the best we understand).