AAMJIWNAANG FIRST NATION, Canada — Growing up with smokestacks on the horizon, Ada Lockridge never thought much about the pollution that came out of them. She never worried about the oil slicks in Talfourd Creek, the acrid odors that wafted in on the shifting winds or even the air-raid siren behind her house whose shrill wail meant "go inside and shut the windows." Now Lockridge worries all the time. A budding environmental activist, she recently made a simple but shocking discovery: There are two girls born in her small community for every boy. A sex ratio so out of whack,...