talking about the concept of intelligent aliens:

Physics and chemistry are a constant everywhere the universe, and DNA is likely standard.

Check back with humans in a billion years and we will probably evolve to some other higher form of life that would be unrecognizable to humans today.

and manipulate that world, you have to have a certain kind of structure.
Exoskeletons have size limitations. To generate energy in a body above a certain size, you need systems for chemical and gas exchange that require flexibility. Bilateral symmetry seems a natural result for most kinds of locomotion.

Soft bodied molluscs, for example, may be quite intelligent, but how much physical building can they achieve?

OTOH, once species have fully developed their externalized technologies, maybe they evolve into softer bodies forms, dependent on the machines they built.

... extraterrestrials build their own personal universe and move on out of this one before the lions and tigers and bears find them and eat them.

Fortunately this is a very big universe and it's not too likely we'll be found by the predators before we become extinct by our own ignorance, become fearsome space predators ourselves, or build a custom universe of our own, beyond the reach of this universe.