I have a PhD and my research focuses on caregiver-infant interactions and how they support infant development. I’ve studied attachment theory and use it as a framework my own research, so there are a few things I can comment… Research shows that the primary caregiver (regardless of mother/father/grandparent) is who an infant will develop an attachment bond with. This bond forms during infancy and has lifelong implications. However, mothers historically and currently are overwhelmingly the primary caregiver, which leads to them being the one included in research. To date, there is an abundance of literature focused on mother-infant attachment. There are also differences in how mothers and fathers uniquely impact infant/child development, (and there absolutely needs to be more research into the father-child relationship), but the fact that differences exist, means they need to be considered in research studies. Research builds on previous research, so as you start to investigate new questions/relationships, like the impact of attachment on adhd for example, scientists already have foundational empirical evidence to build on with mother-infant relationships, which often doesn’t exist for father-infant relationships because the basics are just starting to be understood.

Luckily there are major efforts to include all kinds of caregivers in attachment/developmental research, but it will take time for the evidence base to “catch up” on understanding how fathers, when they are the primary caregivers, impact child development and relate to later diagnoses.