According to this article, coalition airstrikes are killing 1 000 IS fighters a month:

Overall, Operation Inherent Resolve (the U.S.-led combined joint task force in Iraq and Syria) is killing about 1,000 ISIS fighters a month. The death toll roughly matches the number of new recruits ISIS is able to field each month, effectively capping its manpower strength at about 30,000 to 40,000 fighters.
That sounds rather extreme. But if it is true, and IS fighters also happen to have lower empathy levels and higher psychopathy scores than average, it would in effect be a eugenics program.