1) in terms of biology, a successful species is the one that survived: so human species is successful because it survived in big numbers
2) humans evolved on savanna, in Africa so one such pressure would be being able to spot predators from a distance - it contributed to us being upright
3) now the pressure is access to limited resources - food and technology
4) I think the pressure will be good-quality food and quality of life and the way it will influence humanity is by forcing people to have less children