The rate of cooling of the Earth’s interior, the gravitational interactions with other objects, and a steady increase in the Sun's luminosity is well documented.
The sun is just another star, and the basic of star phases is good understood. The sun will eventually burn up most of its fuel and enter a red giant phase that destroys the Earth if we don't intervene [0].
And there's still selection pressure from so many sources. Partial list: Some people die before they reach breeding age, some people refuse to have children, some people are born unable to have children, some people have children with dead-beat spouses, some people are simply incapable of caring properly for kids, some people are prohibitively undesirable as mates, and so on.