Anything placed in the path of reproduction is a barrier to be overcome.
If there is anything in the human genome that correlates with a positive desire to choose to have children, we are selecting hard for that right now. We may see a bottleneck this century and then a gigantic population explosion next century as a result, with a world full of people with very loud "biological clocks" who just adore and crave babies.
That is assuming this is genetically determined enough to be a target for selection. There are probably correlates that are, and I could speculate endlessly about what they are, but I also know that such speculations are likely to be wrong because these systems are complex and often counter-intuitive.
One I've speculated about recently is negativity bias. It seems to me that a lot of people choosing not to have kids right now are doing so because of negativity bias, because they see the world as a terrible place as a result of their consumption of negative media. Historically negativity bias may be something that's been selected for, but this may now have flipped. Optimists may have higher fitness now while pessimists did pre-industrialization and pre-modernity. But again, speculation.
Abortion beats a strong selection pressure.
Only within a lifetime.
Over several generations, it doesn't beat selection pressure, is selection pressure: people who want (or are willing to get) abortions get selected against.
This needs to be carefully qualified. Infant mortality rates for the first 99% of human history were so shockingly, stupefyingly high, that a woman might only expect to have about three of her children survive to adulthood (and maternal mortality rates were also so high that a woman wouldn't expect to survive more childbirths than 5 or 6).
What this means is that the human population was only marginally above replacement for the majority of human history. Human population didn't explode until the medicinal revolution.
1. https://acoup.blog/2025/08/08/collections-life-work-death-an...