Christians remained the largest religious group in the world in 2015, making up nearly a third (31%) of Earth’s 7.3 billion people, according to a new Pew Research Center demographic analysis. But the report also shows that the number of Christians in what many consider the religion’s heartland, the continent of Europe, is in decline. Christians had the most births and deaths of any religious group in recent years, according to our demographic models. Between 2010 and 2015, an estimated 223 million babies were born to Christian mothers and roughly 107 million Christians died – a natural increase of 116 million.