To his credit, intentional or not, according to his CV [1] he's only advised four PhD students and hasn't advised any since 2004. Four students per advisor lifetime might even be below replacement rate for having enough professors.
Replacement rate is highly field dependent. Certain fields (e.g. applied math, some physical sciences) have excellent career prospects for PhDs in industry, in which case the number of lifetime advisees for a given professor can greatly exceed 1 while remaining under the replacement rate for academia. Other fields have much worse prospects for PhDs outside of academia, in which case the replacement rate is much closer to 1. (Granted, there’s always a fudge factor to account for people who do PhDs just for fun.) I’m not sure where Turchin’s field (ecology/evolutionary biology) falls on this spectrum.
It’s important to point out the obvious: the replacement rate for academia is exactly 1 PhD student with faculty aspirations per lifetime of each professor. Anything >1 and academia must grow exponentially to accommodate every single PhD student who desires a faculty position. It is shocking how little this basic, obvious fact is discussed within our ivory towers.
But in a very utopian way isnt this what is desired? Its 2020. Shouldnt the year 2020 have a population composed of 30% scientist doing nothing but long term research? It wont be exponential forever. Eventually you would get professors that do pure research or teach classes with only 3 students.
>Anything >1 and academia must grow exponentially to accommodate every single PhD student who desires a faculty position.
Isn't it implied that only the best PhD students will get a faculty position? How do you choose the best one if you only let one student enter a PhD program?
This is exactly Turchin’s point: by the inherent nature of hierarchies, few people on the bottom are qualified for a spot at the top, but many fields (especially academia) have no way of effectively absorbing those who don’t make the cut, leading to disenchantment.
This is particularly bad in academia because a lot of professors intentionally take on more PhD students than can possibly fill future roles for which a PhD is necessary, in order to use them as cheap labor. This is especially true in the biological sciences: rather than hiring career staff scientists to run experiments, professors simply use their much cheaper grad student labor pool.
Assuming sustained US population growth rates at the current 0.6% per year (big assumption), we expect the population to grow by ~23% over the course of a 35 year academic career. So to sustain the current relative size of academia the replacement rate is not too off from 1 student per advisor lifetime.
What the exponent should be is a whole other matter.
[1] http://peterturchin.com/curriculum-vitae/