It's almost ironic that progressives may one day become a minority while conservatives will become a majority again, purely because traditional gender roles ensure the continuation of those values to future generations. We're not yet at the point where we can beat nature on this matter.
It should be clear that a non-zero percentage will do so, and those that do not will fall victim to the same diminishing population, therefore the trend holds.
Conservatives in the west have 60% more children than liberals. Conservativism is also linked to specific brain structures [1]. These are arguably somewhat heritable, but of course also shaped by environment. Most children of conservatives are conservative until they reach college, where the strong liberal bias in academia changes some of their minds [2].
[2] This bias is well known by the way, this is not a conservative talking point. See Jonathan Haidt's talks on this point, and why this bias is bad for society.
It's even more extreme based on religion. Globally, the birth rate for Muslims is 2.9 children/woman.[1] (But it used to be above 4.) Haredi Jews are at 6.9 per woman, down from 7.5.[2]
