Final answer:
The change in handshape from ages 1 to 9 is part of children's development, involving finer motor control and opposition of the thumb, which is rooted in early limb development and rotation.
Step-by-step explanation:
The handshape change observed in children "ages 1 to 9" involves the development and coordination of fine motor skills, particularly the opposition movement of the thumb toward the fingers of the same hand. This physical change occurs in the context of the expansion of the distal limb buds into a paddle shape during early embryonic development and subsequent differentiation into areas such as the palm and fingers, including the appearance of hyaline cartilage models of future bones. Furthermore, during the seventh week of development, a critical developmental event occurs where the upper limb undergoes a rotation by 90 degrees laterally, positioning the thumb laterally which is essential for that opposition movement.
Through infancy and early childhood, the ability to grasp and hold objects becomes refined, coinciding with the development of other motor skills and the proportional growth of the limbs relative to the trunk.