1 in 50 million chance... world population of 8 billion... average yearly birth rate of 19 per 1000... that would make it 3 per year of these cases! I wouldn't've expected so many double-featured individuals being out there 😯
Assuming 53% of population are females that is 12.7 million with the condition. Using your 19/1000 that's 241k babies a year under this subgroup. Maybe it is 1 in 50 million chance for those 241k babies a year? Still seems off though I did pull the 53% out of my butt but I vaguely remember there being a slightly higher % of females in the total population.