This is not a reasonable reading of this paper, and it also goes against what is already medically known about male hormone levels, which do indeed fluctuate. M

This is not a reasonable reading of this paper, and it also goes against what is already medically known about male hormone levels, which do indeed fluctuate. Men do have a hormone cycle. This paper doesn't dispute that - it merely makes the (possibly surprising) finding that a change in testosterone levels does not correlate with a change in sexual behavior. It does, however, note that fluctuating testosterone levels still affect sexual desire, only it seems to show that an increase in testosterone predicts a reduction of sexual desire: > While there was no significant cross-effect of sexual desire on testosterone levels in our data, there was an unexpected negative cross-effect of testosterone on sexual desire (electronic supplementary material, table S2). Specifically, higher levels of testosterone were associated with lower future sexual desire. This finding, contrary to our expectations, is displayed in the discrete-time plot of results (figure 2b), where cross-regressive estimates are standardized for interpretation. Shown by the testosterone-desire line (solid blue line), a 1 s.d. increase in testosterone predicted a significant decrease in sexual desire, peaking (estimate = −0.12) at around 0.7 days later.