I am one of the few people among my friends who is an only child.  
SO thankful I am an only child with no siblings
I wonder what percentage of people are only children
Not sure but the term applies to people who have never had any siblings at all
I am aware.  I wonder if that means step brothers and sisters too
You can have step siblings or half siblings but still be an only child
So half siblings aren't considered real family?
Correct and throughout history only children are rare
I am sure that back then they wanted to reproduce as much as possible
20th century, birth rates and average family sizes fell sharply, for a number of reasons including increasing costs of raising children and more women having their first child later in life. The proportion of families in the U.S. with only children increased during the Great Depression but fell during the Post–World War II baby boom. After the Korean War ended in 1953, the South Korean government suggested citizens each have one or two children to boost economic prosperity, which resulted in significantly lowered birth rates and a larger number of only children
who can possibly save someone's life and I am able to do it at relatively little cost to myself but fail to do so, I have no way of justifying my behaviour to others. If I am one among millions who can save the life of a Bengali orphan by giving to charity, then I only have a limited obligation to that child compatible with others having a similar obligation. That is, I need not reduce myself to the level of marginal utility to help that child: all I need to do is