Irresponsibility is a genetic and evolutionary certainty. People who are irresponsible and don't think things through are much more likely to have kids at a very young age, have more kids than they can support, and have kids they don't know about. These kids, in turn, will also have these traits.
How did we survive this long?
Hmmm I guess one question I have is are you including plain ignorance with irresponsibility? There's still lots of girls in north america that believe the bullshit they're fed - can't get pregnant if it's your 1st time etc etc and at least with teenage parents there's a large portion of north america where birth control still isn't taught in schools or if it is, often it's way too late.
The adults need to get with the program if they want to stop history from repeating itself.