One supports the other. The clones grow in their pond, keeping the crew alive until the mission's completion, and the tubules transfer the sum total of their memories, ensuring each successive generation benefits from the life experiences of those that came before. Unable to improve the speed of their travel, but desiring a crew that would function for the length of the journey, humanity, as before, found a way to get what it wanted. Unsurprisingly, they failed to consider the cost. Not simply what a seemingly endless journey might do to a group, but to a mind.
The human brain is not built to go on forever; when the body dies, the mind goes quickly. If the spirit endures, translates itself someplace different, then could moving the mind from one body to another trap the soul? Does a soul ache for freedom, does it despise bondage? Philosophers and people of faith may ask these questions, but do men of science?