While I'd prefer avoiding a longer discussion of this myself here, my own view is that interplanatery and/or interstellar travel by lifeforms is far more likely to happen at the bacterial level than primate / mammalian.

As a mode to ensuring life proceeds, possibly. Humans: less likely.

Given the nature of a few past evolutionary bottlenecks (cyanobacteria ⇒ anaerobes, mitochondrial symbioticism, single-cell ⇒ multi-cell, this might represent a significant evolutionary acceleration on other worlds.