I once saw a documentary about Bedouin tribes that were dying out. The problem was very simple, from the outside; they were killing virtually all of their female children.
The team interviewed an elder of one tribe, asking him about this practice. As expected, the elder said that parents wanted sons to continue their family names.
"If no-one in the tribe has any daughters, where will these sons find wives?" asked the interviewer. The elder confidently replied without hesitation, "They will get wives from other tribes." "But what if the other tribes kill their female babies just like your tribe does?" the interviewer persisted (In fact, they had met people from several tribes, and indeed they all followed this terrifying practice). The elder looked at the interviewer like he was a slow child. "They will get wives from other tribes."