An interesting claim, but deeply flawed. Sadly Lynn has previously argued along racial lines claiming black races are genetically inferior to white people, but this is false. The difference between levels of IQ in ethnic groups has far more to do with opportunity and resources than genetic difference.
And this is so with faith as well. Christians are forced to put their children through a secular education system that is often hostile to their faith, and even when not openly questioning Christian belief through secular assumptions, there is often a general undercurrent of negativity towards faith. Many Christian children switch off from the secular humanist dominated education system because of a lack of trust in what is being taught (although it should be noted that there are some very good Christian teachers in the state education system). But is it any wonder that Christians have less opportunity to pursue academic careers under these circumstances? Having said that there are many Christians with good qualifications and higher degrees and leading fruitful professional lives. Religious believers were also instrumental in developing science.
Two responses in the Telegraph.
Chris Howse 'Clever people are atheists. Cleverer ones aren't'
George Pilcher ' 'God is not for the stupid' say Chistianity's clever people.'