Behavioral trait patience reduces cost of interest and societies preferring productivity select for patience.

From Selection, Patience, and the Interest Rate by Radoslaw Stefanski and Alex Trew.  From the Abstract:

The interest rate has been falling for centuries. The key to explaining this decline is increasing societal patience, driven by a process of natural selection. Three observations support this mechanism: patience varies across individuals, is inter-generationally persistent, and is positively related to fertility. To establish the importance of this channel, we introduce a dynamic, heterogeneous-agent model of fertility. The structure of our model enables us to use modern, micro level data to calibrate the historical distribution of patience. Our quantitative results match the centuries-long fall in the interest rate, highlighting the crucial role of selection in this historical, and ongoing, trend.

If this is saying what I think it is saying it makes me a little nervous.  I am interpreting this to mean that 

1)  The interest rate has been falling for centuries

2)  The behavioral trait of patience contributes to a lower interest rate

3)  The behavioral trait is heritable

4)  Productive societies select for the trait of patience.

Possibly a  Just So story.  Possibly directionally true.  Certainly plausible.

Plausible but unproven, I'd say.