I believe it tends to either be constant or slightly positive, actually. Of course, if all you want is happy people, happiness is heritable and so you can do em

I believe it tends to either be constant or slightly positive, actually. Of course, if all you want is happy people, happiness is heritable and so you can do embryo selection on it or genetically correlated traits like personality factors (for Extraversion & against Neuroticism: https://www.cambridge.org/core/journals/twin-research-and-human-genetics/article/personality-polygenes-positive-affect-and-life-satisfaction/4DB2BE673BF122FB9A0AF2147EED80C0/core-reader https://www.cambridge.org/core/journals/twin-research-and-hu... )