In the film "Doctor Strangelove and …" (1964), Peter Seller plays three roles: A British officer at a US military base, trying to avoid the third world war, the US president and Dr. Strangelove, the scientific Adviser to the president.
In the short video below (1m50s - I added subtitles) we see the outline of what "longtermists" like Elon Musk mean, when they talk about "taking humanity into space" and "preserve the human species".