Turkana Boy or KNM-WT 15000 was discovered in 1984 by Richard Leaky’s team in Kenya. He would prove to be a very important find, being around 40% complete having most of its skull, long bones and hips. And bases on his osteology I would say that him and Homo erectus where not that different from us the neck down, and explain his species importance to us. Here is why.
Neck down he had a body plan that was almost exactly like our. He was only around eight or nine when he died but based on the bones and teeth the species had a slightly faster growth rate then us. But even at eight he was around 5 foot 3 and still growing. His hips where shaped like ours and he also had long legs and shorter arm like us suggesting that he was completely bipedal and his species being adapted completely to the ground. Fossilized footprints from another member of his species dates back around 1.5 million years ago proving that they had a similar gait and stride to us and that they were capable of long distance walking and running.
Based on Turkana Boy they also had adapted to the very dry hot climate of East Africa. He had a narrow slender body with long legs and arms. This reflects what is called the Bergman Allen rules. Which can be seen in, especially mammals, species around the world. The hotter dryer environment to help dissipate heat its better to have longer limbs(Allen) and slender shoulders and hips(Bergman). You can still see this in modern day humans living in the opposite extreme environments like the Inuits of North America or the aboriginals of Australia.
I can also make some assumptions about their physiology. I think Turkana Boy and Homo erectus had the adaptive cooling mechanism to sweat. Sweating had to of originated in the hot dry environments of Africa. This type of cooling mechanism doesn’t make sense in a hot humid environment because there is to much water in the air already for sweat to evaporate efficiently to get rid of heat. It defiantly doesn’t make sense for it to originate in a cold environment. His long limbs also reflect that with longer limbs means more sweat glands and ability to effectually stay cool in a very dry environment. And if they had sweating as a cooling mechanism they would also have been hairless one the body similar to today. Because for sweating to work there skin would need more exposure to the sun so sweat can effectively evaporate taking heat with it. One last assumption, if they were sweating and had less body hair their skin would need protection from the sun and they mostly likely had abundant amount of melanin. And with this strong selective pressure to be protected from the intense UV rays of the sun they would have had dark skin.
To modern day we are still very much bipedal. We are still the “hairless apes.” And even though I don’t like it on a humid Midwestern summer day we are also still able to sweat which might have all started with our ancestors like Turkana Boy.