What evolutionary change occurred alongside the increase in brain size in humans?

What evolutionary change occurred alongside the increase in brain size in humans?

• A. The gut became 60% smaller.
• B. The gut became 60% larger.
• C. The gut size remained the same.
• D. The brain became smaller.

Answer: (A)

Rising brain size in humans is best understood as a trade-off in energy use within the body. The brain is energetically expensive, so when early humans started to eat higher-quality, easier-to-digest foods (a result of cooking and processing), they could extract energy more efficiently. That extra energy didn’t have to support as large a gut, so the digestive tract could shrink. The energy saved by a smaller gut could then be redirected toward brain tissue, enabling its growth. This pattern—a brain that increases in size while the gut becomes smaller (often described as about 60% smaller)—fits the observed energy-allocation shift in human evolution. If the gut didn’t shrink, or if it grew larger, there wouldn’t be the same budget available to support a bigger brain.

Rising brain size in humans is best understood as a trade-off in energy use within the body. The brain is energetically expensive, so when early humans started to eat higher-quality, easier-to-digest foods (a result of cooking and processing), they could extract energy more efficiently. That extra energy didn’t have to support as large a gut, so the digestive tract could shrink. The energy saved by a smaller gut could then be redirected toward brain tissue, enabling its growth. This pattern—a brain that increases in size while the gut becomes smaller (often described as about 60% smaller)—fits the observed energy-allocation shift in human evolution. If the gut didn’t shrink, or if it grew larger, there wouldn’t be the same budget available to support a bigger brain.