There are two dysgenic trends currently operating:
Populations with lower IQ have higher fertility rates. This is the main reason, why the average IQ is lower whenever a new version of the IQ-database is published .
Within almost all populations the fertility patterns are dysgenic because smarter people (mostly educated women) are having fewer kids.
Over time this should lead to exponentially fewer very high IQ people. However, this doesn’t seem to be happening just yet. Mathematics for example is enjoying a golden age, with century old problems being solved. The main reason for this is likely increased assortative mating.
Assortative mating is currently increasing mostly due to urbanization. The more ambitious and more capable people are drawn to the cities, often to study and ultimately to work, marry and have (too few) kids. The same mechanism also holds between countries with high IQ immigration, i.e the more ambitious and capable people from the global south are drawn to the economic powerhouses in the global north.
Additionally social segregation ensures that people marry within the same class. Via gentrification and similar dynamics, more affluent people take over or maintain a grip on the nicer quarters.
This is also ultimately a result of urbanization. If you are rich in a village, you live in the biggest house, but if you are rich in a city you live among your peers, spatially segregated from the lower classes.
One impressive example for the effect of these mechanisms is the intellectual output of Budapest’s jews in the first half of the 20th century. Before the Holocaust roughly a quarter of 800,000 Hungarian Jews lived in Budapest. These 200,000 people produced a handful of super geniuses that together among many other things build the first atomic bomb . It is certainly plausible that stronger assortative mating and a certain amount of self-selection of city dwellers raised the number of geniuses in Budapest even beyond what one could expect from 200.000 people from a group with an average IQ of probably around 110.
Of course in the medium term covering our need for technological and scientific geniuses via increased assortative mating is not sustainably. Let’s hope it lasts until we engineer our way out of the dysgenic dilemma.