Final answer:
The average human brain has a volume of roughly 1.1 liters, which suggests that a cranial capacity of 1000 milliliters is less than the average for modern humans, likely indicating earlier human ancestors or hominins. The brain has evolved to fit more gray matter within the limited space of the cranial cavity due to extensive folding in the cerebral cortex.
Step-by-step explanation:
The question 'Who has a cranial capacity that averages 1000 ml?' is referring to the volume of the cranium, which is an indicator of the size of the brain. However, the average human brain has a capacity slightly larger than this, with a typical volume of roughly 1.1 liters, equivalent to 1100 milliliters. This implies that a cranial capacity of 1000 milliliters would be less than the average for a modern human, and could relate to earlier human ancestors or certain hominin species based on the fossil record. For reference, it is mentioned that an adult male has an average blood volume of 4.7 liters, which is 4700 milliliters, illustrating that cranial capacity is much smaller in comparison to total blood volume.
Further understanding the brain, it is critical to recognize that despite the limited cranial cavity space, the brain has extensive folding in the cerebral cortex allowing more gray matter to fit. This efficient organization enables the human brain with its various functions, like transmitting information through neurons, managing body functions, and processing cognitive activities. The compact nature of the brain, with its large surface area of gray matter if laid out flat, showcases the complex evolution of brain anatomy catering to functional and developmental constraints, such as the size of the birth canal.