prob not a biological entity...

"The thought of long-term galactic survival for humanity was comforting to some, and in any case it seemed inevitable, humanity’s fate or destiny.

there is no Planet B,Earth is our only home.

This conclusion, startling to some, obvious to others, has ramifications that are worth pondering. If it comes to be a generally agreed on view, it might change how we act as individuals and a civilization. These changes in behavior might turn out to be crucial for our descendants."

Kim Stanley Robinson on generation ships and hazards

http://boingboing.net/2015/11/16/our-generation-ships-will-sink.html