Both had their origins in modern science. But they proceeded by and large independently. The net result is a fall in the birth rate to match the fall in the death rate, and a worldwide human population that will approach stability over the next century. And I fear that fertility will not decline completely in developing countries until well after modern economic growth has taken hold. Moreover, I suspect that the complex set of institutions that make for liberty, innovation, and growing prosperity is more fragile than Easterlin does.
Economic growth is indeed triumphant, but to no point.
Easterlin believes that people are no happier today in their relative material abundance than they were three centuries ago in their relative material poverty. Indeed, Easterlin believes that people are not happier today in the U.S. than in India. Happiness is attained when you achieve your dreams and solve your problems. Material abundance helps you do so, but it also teaches you to dream bigger dreams and pose yourself more complicated problems. People used to think that material progress would lead to material satiation.