For two hundred and ten years, Bnei Yisrael were in Egypt. 70 souls entered, among them only 2 unmarried women (Dina and Serach) and also Yocheved who is said to have been born right at that moment.
If we take Jacob and his sons out of the equation (of those who will continue to procreate from that moment), we have 54 males (at least one with a wife, since Perez came in with sons) and 3 females. From these came forth millions within the next 210 years.
Were there actually more than 70 souls (if so, why are only 70 mentioned?)? Did each couple have an abnormal amount of children (as far as I know, not a single couple such as this is mentioned in the Torah)? Was it something supernatural?