Perhaps because I’m adopted, I have always been confused by the metaphor of blood relation. The metaphor is anatomically absurd. No one literally shares the blood of their parents, their siblings, or other family members. It should be clear to anyone with a basic knowledge of the facts that one cannot possibly share any blood with one’s father; sperm, being themselves single cells, cannot have blood. And investigation teaches one that one does not, except in rare cases, share any blood with one’s mother, either. A mother’s body transfers nutrients and wastes across the placenta, but for important immunological reasons, no blood is traded. Hence, one also shares no blood with siblings, grandparents, cousins, etc., except in the case of deliberate transfusion or unusual medical accidents.
Yet the metaphor of blood remains widespread, long after the time when physiology might have been thought to dispel it—maybe by the same vestigial logic that allows us still to speak of people as “good-humored” or having a “warm heart.” Languages may never outgrow such notions. Still, I cock an eyebrow often at the many places this metaphor appears in our pop culture: “the blood of the Targaryens runs in Jon’s veins,” “my flesh and blood,” “any blood descendant of the House of Windsor, regardless of gender,” “Your blood in [Voldemort’s] veins, Harry, Lily’s protection inside both of you!” (First three examples not direct quotes from anything, but you get the idea.)
I’ve even come to think the adjective “biological” in such circumstances is a little odd or inaccurate: “biological relative,” “biological family,” and so forth. When we use this shorthand, we mean something like “first-degree relatives”; but there is no reason why more distantly related humans are not “biological.” They’re certainly not synthetic or robotic. “Biological” gets tossed around as a modifier in all kinds of weird ways (“biological weapon,” “biological clock,” “biological engineering”); here, as in some of those, the idea seems to be that the biological is synonymous with, or at least proximate to, the natural. (So a biological weapon or warfare uses things that derive from nature rather than artifice; a biological clock is distinct from human-imposed mechanical time-keeping; a biological family is distinct from one created by artifice, law, or culture.) Yet fostering young that one didn’t conceive is a behavior seen across many animals. So it seems odd to oppose the adoptive, legal, or synthetic to the biological in this sense.
More accurate, to my mind, would be terms such as “conceptive parent,” “conceptive sibling,” “extended conceptive family,” etc. However unlikely to catch on, it seems far more precise to invoke the act in question—conception—rather than the vague idea of “biology,” however debased it may already be. It’s certainly far closer to the mark than any term involving “blood.” I generally shun neologisms, and in an age where people already constantly struggle to keep track of new terms to avoid insulting or hurting others, I wouldn’t want to impose this little invention on anyone else. Nevertheless, for the punctilious, or at least the linguistically-minded, I think it’s a reasonable and perhaps superior alternative.