SAT Practice HONORS

Marsupials Lend a Hand to Science

Marsupials (mammals that carry their young in a pouch) are a curiosity among biologists because they lack a corpus callosum, the collection of nerve fibers connecting the two hemispheres of the brain. In most other mammals, the left hemisphere of the brain controls the right side of the body, the right hemisphere controls the left, and the corpus callosum allows communication between the hemispheres. Scientists are long believing that this structure enables complex tasks by sequestering skilled movement to a single hemisphere without sacrificing coordination between both sides of the body;

• Correct as is

• will long be believing

• have long believed

• long believe

this sequestration would explain handedness, the tendency to consistently prefer one hand over the other, in humans.

• Correct as is

• and favor the use of one hand over the other,

• one hand over the other that could be chosen,

• one hand on a regular basis,

However, a recent finding of handedness in marsupials suggests that a trait other than the presence of a corpus callosum links as handedness: bipedalism.

• Correct as is

• trait,

• trait;

• trait: