(1) In the past, e.g., in tribal or agricultural communities, women had children whether they really 'wanted' to or not.
(2) Now in more industrialized countries, a significant fraction of women have some options. Some women still have children but some women do not want to have children and do not.
(3) The change in number of children per woman is a 900 pound gorilla in the room: The article mentioned numbers under 2 children per women with a rate a low as 1 child per woman. There is some recent data that Finland is at 1.5 children per woman.
Of course, for any rate much under 2, each 20 years or so the population will be going down significantly. "Get your old houses, furniture, dishes, baby clothes, etc. cheap, cheap, cheap!".
So, net, heavily women who don't want to have children won't. These women will be 'weak, sick, dead limbs on the tree' and will be pruning their genes from the tree. What will be left are women who, given the choice, actually, effectively WANT to have children.
The big point: After a few such generations, we will be left with a much smaller population with many fewer women but nearly all of whom WANT to have children. Then the population will start growing again.
One more big, surprising point: We are now, in much of the world, in the most rapid change in the gene pool of the last 40,000 or so years.
Where did the 40,000 come from? Humans walked out of Africa back there somewhere. At one point, ballpark 40,000 years ago, they reached, say, India. One branch went west to Western Europe, and another branch went east to China and Japan. Mostly the two branches haven't much mixed since then.
Okay, at the common branch, ballpark 40,000 years ago, what were women like? Well, take women from Japan and women from Western Europe. Take some 'characteristic' in common, say, desire of a major fraction of the women, given an economic opportunity, not to have children. Now, start in either Japan or Western Europe and count genetic 'changes' on this 'characteristic' going backwards in the tree to the common branch, about 40,000 years ago, and, then, continuing to count changes, going forward in the other branch of the tree to the present.
So, if on this characteristic the women in Japan and Western Europe are close, that is, have few changes, then on this characteristic the common ancestor 40,000 years ago has still fewer, that is, is closer to the women in both Japan and Western Europe than they are to each other.
Net, since a significant fraction of women in both Japan and Western Europe will, given an economic opportunity, choose not to have children, that is, these women are close to each other, both are still closer to their common ancestor 40,000 years ago. So, for 40,000 years, many women had children not really because they 'wanted' to but because of economic necessity.
So, now that women who don't really want to have children are being pruned from the tree, we are, on this characteristic, in the most rapid change in the human gene pool of the past 40,000 years. And, the change is VERY rapid, should have a huge effect in just a few generations, say, just 100 years, which on the scale of 40,000 years, is FAST.