That doesn't follow. The delay in marriage is apparently economic - so apparently people have about the same resources when they marry as they always have, it just took them longer to accumulate. Also, the biological pressures on those wanting children may be causing some people to marry after postponing as long as they reasonably can - with less in the way of financial resources, not more. They won't necessarily live longer, in consequence (humans already live far longer past fertility than any other organism I can think of - that's a big cushion). At any rate, that will take thousands of years to show up. And a fourth: poorer physical outcomes, as measured in the health of the mother and the child (including the age-related detriments of an older father). And a fifth: the wealthy - who have the greatest impact on the environment - will produce a higher proportion of the children than otherwise (via concubines etc, as well as marriage, since they can afford to. ). Yet another advantage of wealth made more influential. And a sixth: older, less capable grandparents - recognized now as an important factor in human child raising.