In most countries around the world it is convention that the wife take the husband’s surname at marriage. It is equally conventional for a child to then also take this same name. Evolutionary psychology is the reason behind this phenomenon, as discussed briefly in the book Why Beautiful People Have More Daughters.
One of the author’s reflects further on this idea in a number of posts looking at why wives and children take their husband/father’s last name.
Nature may or may not help the father convince himself of his paternity by making the baby (kind of) resemble the father rather than the mother. However, [â€¦] people (especially maternal kin) appear to help, by telling the father that the baby resembles him, regardless of whether it does or not. [â€¦] After all, the maternal kin, unlike the paternal kin, have no interest in finding out the truth. They know that the baby is genetically related to the mother for sure – there is no such thing as maternity uncertainty – and all they want is to make sure that the father is convinced of his paternity enough to invest in the offspring, regardless of whether or not he is the actual genetic father.
The convention of giving the child the father’s last name is another means for the mother and her kin to convince the father of his paternity.