In a new book out by Emeritus Professor Robert Le Vine and his Research Fellow wife Sarah, they examine parenting across different cultures and explores this challenging issue. Whilst attachment theories dominate the field this research questions this idea. A culmination of their lives work, the Levine's comprehensive studies examines how in each culture, parents attempt to provide optimal parenting for their children. But what is considered optimal varies enormously from culture to culture. (Spoiler alert: Whenever a newspaper headline or book title is in the form of a question, the answer is invariably "no.")
Another study by Oxford University and the London School of Econmics was published recently. This study found that children who entered into early years nursery care or the care of their grand parents whilst their parents worked, showed higher levels of developmental attainment. Again, such research challenges the widely held belief in attachment theory that is popular in the field. You can download the report from here.