The older that such fish become, the more mercury they may have absorbed. Anything that eats these fish within the food chain also consumes the higher level of mercury that the fish have accumulated. This process explains why predatory fish such as swordfish and sharks or birds like osprey and eagles have higher
The goal, then, when it comes to having a boy is to increase the likelihood that a Y chromosome sperm reaches the egg first. Many medical researchers believe that Y chromosome sperm are faster swimmers, but that X chromosome sperm have more endurance.
The same thing is true in having a boy or a girl. Mom's body can't remember what sex the previous child was. So the chance of one child being a boy or girl is independent of any other childâs gender in the family. It's just a matter of which type of sperm happens to reach the egg first.