Short answers, pulled from the story.
A parent is either the biological progenitor of an offspring or, in humans, a caregiver or legal guardian who raises a child without a biological connection. The most common types of parents are mothers, fathers, step-parents, and grandparents. Advances in assisted reproduction have made it possible, in some cases, to have more than two biological parents.
Parents share 50% of their genes with their offspring. This is why parents are classified as first-degree relatives.
Parent-offspring conflict is a theory proposed by Robert Trivers in 1974. It describes the evolutionary tension between parents, who tend to maximize the number of offspring they produce, and each individual offspring, which can increase its own fitness by obtaining a larger share of parental investment. The theory extends the selfish gene theory and has been used to explain phenomena such as siblicide in birds.
Paternity is tested through DNA analysis, also known as genetic fingerprinting, which uses polymerase chain reaction and restriction fragment length polymorphism. Older methods included ABO blood group typing, analysis of proteins and enzymes, and examination of human leukocyte antigens. Genetic fingerprinting has largely supplanted earlier forms of testing.
As of 2011, social science literature mostly rejects the notion that there is an optimal gender mix of parents. Major professional associations agreed in 2009 that there is no well-established evidence that children with same-sex parents suffer developmental disadvantages. Family processes, such as the quality of parenting and relationships within the family, are more significant predictors of children's well-being than family structure.
In Europe, parents are generally happier than non-parents. Among women, happiness increases after the first child, but having additional children beyond the first is not associated with further increases in well-being. Happiness appears to increase most in the year before and after the first childbirth.