I consider this to be another great argument against the existence of "galactic civilisations". Every colony would necessarily become a the seed for a different

I consider this to be another great argument against the existence of "galactic civilisations". Every colony would necessarily become a the seed for a different civilisation and species in a comparatively short amount of time. Isolation due to the communication delay (e.g. ~8 years round-trip in case of Earth to Alpha Cen) and the likely need for adaptation to the new world (be that by means of evolution or genetic engineering) would drive both home world and colonies apart quickly.