The dictionary defines posterity as: All future generations of people or the descendants of a person.`
By default all creatures of God procreate for posterity or the continuance of life. Humanity is unique. We have the ability to improve the future generation not just through evolution but with our ability to write (compose) and build. We have the ability to teach and learn. If nobody writes (composes) or builds, then the future generations of humans will only be as the jelly fish in the ocean. Living only based on instinct. Humanity has 12 basic needs. The one that stands out to build posterity is communication.
The improvement and prosperity of future generations are dependent on those with the talent to compose (write) and build. We have the instinct to teach and learn. But this (knowledge) must grow from the foundation of the past generation. Left behind by those who wrote and built. Rote memory can sustain 3 or 4 generations at max with possibility of errors. Hence, languages when not backed up with written words and definitions are either lost or corrupted. However, written words/music (compositions) and built structures can last for multiple generations.
Those who have the talent to write (compose) or build, will always leave something good or bad behind as a foundation for the future generations to learn from. They influence the path of the future generation. Ideologies, science and technology are born and perpetuated based on the teachings and influence of those who wrote (composed) and built.
These talented people who take their time to create, make the languages of the universe available to humanity for future generations to work on and improve upon.