Admittedly I know little about atheism despite my own time trying to be one. Atheism is very much a movement and sentiment based on doubting and suspecting religious practises and stuff but this varies ranging from philosophers to skeptics. Skeptics in particular are a very vocal segment of atheism dedicated to debunking supernatural and religious beliefs and claims.
They’re certainly intelligent though historically they were more commonly found among philosophers than among scientists. Atheism or at least apostasy and disbelief in divinity has existed earlier than it is imagined but as an ideological movement it happened fairly recently especially from the 18th century onwards.
The growing religious debate over evolution presumably had atheism cling more and more to science. This still isn’t the case as there are religious scientists especially in places like India and I do know one before. He’s even a Christian! There are lots of Catholic scientists and it took a Catholic monk to influence the science of genetics.
But atheist scientists are increasingly well-represented and have come to exert a bigger say in science. To the point where science and atheism is increasingly closely linked as certain religious sects withdraw themselves from it for some reason.