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, […] peo­ple (espe­cially mater­nal kin) appear to help, by telling the father that the baby resem­bles him, regard­less of whether it does or not. […] 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.