This paper proposes a developmental approach to social intelligence, especially communication ability, for robots and other artificial systems. Any social being has to have two essential features: naturalistic embodiment - haying a body similar to others, and socio-cultural situatedness - being able to communicate with others and to participate in the social activity. However, we still have an open question: how does the body become situated in the social environment? Our answer is epigenesis, where (1) we create a humanoid with minimum innate abilities, namely a primordial form of joint attention and indirect experience, then (2) through the attentional and imitative interaction with human caregivers, the humanoid autonomously explores how to interact socially with people. As an epigenetic embodiment, the authors are building an upper-torso humanoid, Infanoid, which is to acquire social situatedness in the human community.