Second-degree relative in the context of "Grand-nephew"

Grandparents, individually known as grandmother and grandfather, or Grandma and Grandpa, are the parents of a person's father or mother – paternal or maternal. Every sexually reproducing living organism who is not a genetic chimera has a maximum of four genetic grandparents, eight genetic great-grandparents, sixteen genetic great-great-grandparents, thirty-two genetic great-great-great-grandparents, sixty-four genetic great-great-great-great-grandparents, etc. In the history of modern humanity, around 30,000 years ago, the number of modern humans who lived to be a grandparent increased. It is not known for certain what spurred this increase in longevity, but it is generally believed that a key consequence of three generations being alive together was the preservation of information which could otherwise have been lost; an example of this important information might have been where to find water in times of drought.

In cases where parents are unwilling or unable to provide adequate care for their children (e.g., financial obstacles, marriage problems, illness or death), grandparents often take on the role of primary caregivers. Even when this is not the case, and particularly in traditional cultures, grandparents often have a direct and clear role in relation to the raising, care and nurture of children. Grandparents are second-degree relatives to their grandchildren and share 25% genetic overlap.

An aunt is a female individual who is a sibling of a parent or married to a sibling of a parent. Aunts who are related by birth are second-degree relatives. Alternate terms include auntie or aunty.

Aunt, auntie, and aunty also may be titles bestowed by parents and children to close friends of one or both parents who assume a sustained caring or nurturing role for the children. Children in some cultures and families may refer to the cousins of their parents as aunt or uncle due to the age and generation gap. The word comes from Latin: amita via Old French ante and is a family relationship within an extended or immediate family.

An uncle is usually defined as a male relative who is a sibling of a parent or married to a sibling of a parent, as well as the parent of the cousins. Uncles who are related by birth are second-degree relatives. The female counterpart of an uncle is an aunt, and the reciprocal relationship is that of a nephew or niece. The word comes from Latin: avunculus, the diminutive of avus (grandfather), and is a family relationship within an extended or immediate family. A popular colloquial term in English is Unc.

In some cultures and families, children may refer to the cousins of their parents as uncle (or aunt). It is also used as a title of respect for older relatives, neighbours, acquaintances, family friends, and even total strangers in some cultures, for example Aboriginal Australian elders. Using the term in this way is a form of fictive kinship.

An avunculate marriage (or uncle/aunt-niece/nephew marriage) is a marriage with a parent's sibling or with one's sibling's child—i.e., an uncle or aunt marrying their niece or nephew. Such a marriage may occur between biological (consanguine) relatives or between persons related by marriage (affinity). In some countries, avunculate marriages are prohibited by law, while in others marriages between such biological relatives are both legal and common, though now far less common.

If the partners in an avunculate marriage are biologically related, they normally have the same genetic relationship as half-siblings, or a grandparent and grandchild—that is they share approximately 25% of their genetic material. (They are therefore more closely related than partners in a marriage between first cousins or between granduncle/grandaunt and grandniece/grandnephew, in which on average the members share 12.5% of inherited genetic material, but less than that of a marriage between, for instance, cousin-siblings, in which the partners share 37.5% of their inherited genetic material.)