simplification of organisms

That is a bias again, organisms adapt, some abilities develop at the expense of other possibilites. In the current human context, even if most people are born with less than your ideal of genetic inheritance or raised with different values, many will develop more resources than enough to feed and shelter themselves and others. The only obstacle is state intervention to economic coordination.

This abundance also arguably allows for the most able and skillful parents the most opportunities to reproduce. If resources were scarce these parents would be strugling more for conditions that allow reproduction.

Resources don't allow less productive people to live without consequences. They have to maintain a minimum of responsability and social integration to allow survival. The problem is when political groups redistribute resources to individuals that lack such responsability and social cooperation. They do it for their political gain. The problem is not the abundance of resources, the problem is the redistribution.

even to eventual shortage of resources

If there will be shortages, it might even worsen the problem. But there is no reason why the trend cannot be the opposite. The increase in politically dependent groups don't necessarily mean they will grow indefinetely, nor that the share of resources they forcifully expropriate will always be the same. Productive individuals can resist expropriation, or they can invest in resources that cannot be easily expropriated. If the political groups are surrounding themselves with inept and underproductive groups, their efficiency at expropriating is also diminishing.

The whole problem is not reproduction, but the political alliances and activity. The Bolsheviks killed millions of peasants not because the urban supporters were reproducing at greater numbers, but because their supporters didn't care for mass expropriation after two decades of continuous warfare.