The first being a biological relationship with nature and the second being a social link thus sociology.

Unfortunately they would never know of each other's biological relationship.

But here I must draw a distinction of rather a different kind, namely that between biological relationship and social relationship.

Like mothers, fathers may be categorized according to their biological, social or legal relationship with the child.

Parenting refers to the aspects of raising a child aside from the biological relationship.

Ideas about kinship do not necessarily assume any biological relationship between individuals, rather just close associations.

No actual biological relationship between speakers is implied by the metaphor.

Some experts say they would not trust a test in which the proteins being measured and their biological relationship to cancer are unknown.

It can occur when two people who are unaware of their biological relationship become sexually intimate.

At the time the three were unaware of the relevant biological relationship.