Final answer:
Attachment theory, developed by John Bowlby, emphasizes the importance of a secure bond between a child and their primary caregiver. It has been tested with both primates and humans and has an evolutionary basis. However, it does not specifically describe the emotional relationships between siblings of similar age.
Step-by-step explanation:
Attachment theory, originally developed by John Bowlby, describes the emotional bond between a child and their primary caregiver. It has been tested with both primates and humans, providing evidence of its applicability across species. This theory has an evolutionary basis, as it emphasizes the importance of a secure attachment for the safety and development of children.
However, the theory does not specifically focus on the emotional relationships between siblings of similar age, making statement d. It describes the emotional relationships between siblings of similar age irrelevant to attachment theory.