The short-haired human!
While other primates are furry, human skin is exposed to the elements. It’s not that we’re ‘naked’ – our hair is just really short over much of our bodies. In the warm places where our ancestors lived, evaporation of sweat from exposed skin was a great benefit in cooling our entire bodies. Our brain runs so ‘hot’, in fact, that sweating and cooling proved vital for evolving our big brain.