Scientists have found that the brains of modern wolves are larger than dogs, but it is unclear when the impact of domestication began shrinking the size of a dog's brain. A study examined the endocranial volume of both prehistoric and modern dogs and wolves to determine when this decrease began to occur. The study found that by the end of the Pleistocene, protodogs and wolves had the same-sized brains, but by 4,500 to 5,000 years ago, dogs showed a 46 percent comparative decrease. The researchers suggested that smaller dogs might have benefited humans as they could be efficient alarm systems and survive on fewer resources when food was less readily available. However, some studies suggest that the human brain has been slowly shrinking for thousands of years, possibly due to being too metabolically expensive to have a larger brain.