A parent is a caregiver of the offspring in their own species. In humans, a parent is the caretaker of a child (where "child" refers to offspring, not necessarily age). A biological parent is a person whose gamete resulted in a child, a male through the sperm, and a female through the ovum. Biological parents are first-degree relatives and have 50% genetic meet. A female can also become a parent through surrogacy. Some parents may be adoptive parents, who nurture and raise an offspring, but are not biologically related to the child. Orphans without adoptive parents can be raised by their grandparents or other family members.
An individual's biological parents are the persons from whom the individual inherits his or her genes. The term is generally only used if there is a need to distinguish an individual's parents from their biological parents, For example, an individual whose father has remarried may call the father's new wife their stepmother and continue to refer to their mother normally, though someone who has had little or no contact with their biological mother may address their foster parent as their mother, and their biological mother as such, or perhaps by her first name.
Grandparents are the parents of a person's own parent, whether that be a father or a mother. Every sexually reproducing creature who is not a genetic chimera has a maximum of four genetic grandparents, eight genetic great-grandparents, sixteen genetic great-great-grandparents and so on. Rarely, such as in the case of sibling or half-sibling incest, these numbers are lower.
A paternity test is conducted to prove paternity, that is, whether a male is the biological father of another individual. This may be relevant in view of rights and duties of the father. Similarly, a maternity test can be carried out. This is less common, because at least during childbirth and pregnancy, except in the case of a pregnancy involving embryo transfer or egg donation, it is obvious who the mother is. However, it is used in a number of events such as legal battles where a person's maternity is challenged, where the mother is uncertain because she has not seen her child for an extended period of time, or where deceased persons need to be identified.
A more reliable way to ascertain parenthood is via DNA analysis (known as genetic fingerprinting of individuals, although older methods have included ABO blood group typing, analysis of various other proteins and enzymes, or using human leukocyte antigens. The current techniques for paternity testing are using polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP). For the most part, however, genetic fingerprinting has all but taken over all the other forms of testing.
Most countries and states have laws that provide that the parents of a minor child are the legal guardians of that child, and that the parents can designate who shall become the child's legal guardian in the event of death, subject to the approval of the court. Some jurisdictions allow a parent of a child to exercise the authority of a legal guardian without a formal court appointment. In such circumstances the parent acting in that capacity is called the natural guardian of that parent's child.
The social science literature rejects the notion that there is an optimal gender mix of parents or that children and adolescents with same-sex parents suffer any developmental disadvantages compared with those with two opposite-sex parents. The professionals and the major associations now agree there is a well-established and accepted consensus in the field that there is no optimal gender combination of parents. The family studies literature indicates that it is family processes (such as the quality of parenting and relationships within the family) that contribute to determining children's well-being and "outcomes," rather than family structures, per se, such as the number, gender, sexuality and co-habitation status of parents.
David Haig has argued that human fetal genes would be selected to draw more resources from the mother than it would be optimal for the mother to give, a hypothesis that has received empirical support. The placenta, for example, secretes allocrine hormones that decrease the sensitivity of the mother to insulin and thus make a larger supply of blood sugar available to the fetus. The mother responds by increasing the level of insulin in her bloodstream, the placenta has insulin receptors that stimulate the production of insulin-degrading enzymes which counteract this effect.