There are multiple holes in this argument. The fact that infants are born with genes need not be discounted entirely. As much as their family contributes to their development, so do their genes. Infants are not blank slates, but are born with some genetically-determined traits and temperaments. These influence how the family interacts with them. More social babies elicit more social responses, which increases their sociality. Less social babies are socialized with less, so they grow up to be less social. Therefore, nurture isn’t everything, because our genes determine exactly what kind of nurturing we get.