Homo erectus, the direct ancestor of Homo sapiens, evolved in Africa between 2 and 1.5 million years ago (Mya). He was the same size as us, walked and ran erect. He made Acheulean stone axes for hunting and for scavenging big mammals killed by other predators. He built low stone walls, with animal skin tents above, or lived in caves with fire to keep him warm. He dressed in hide and fur when cold.
Homo erectus was very successful, spread out from Africa and lived all over Europe and Asia. But his brain size was smaller than humans and childhood period was shorter. He used proto language and formed social groups. Total numbers of these hunter gatherers were probably small, maybe 1- 200,000 at the peak, spread out all over Asia, Africa and Europe in small clans.
The Australopithecines and earlier hominins that preceded Homo erectus walked upright when forests in East and South Africa grew drier around 4 Mya, making it necessary to forage outside tree cover. As brain size increased, the period of infancy and childhood increased too, needing prolonged care. Australipithecus became monogamous so that males could forage and carry back food for his family in his hands. Bringing back fruit, nuts and roots with occasional meat made increasing brain size possible – in turn making him a better forrager – a beneficial cycle of walking, carring back better quality food, and increasing brain size.
Human ancestors probably remained largely monogamous after that, unlike Chimpanzees and monkeys. Australipithecus and Homo erectus both show reduced sexual dimorphism. Males and females looked alike and were of similar size, indicating reduced competition for mates. By 2.5 Mya, many parts of Africa changed from scrub or forest to open Savannah similar to the Serengeti plains of today. Herbivores abounded and Homo erectus adopted a predominantly meat diet. His intestines elongated and the cecum shortened, making him a well adapted carnivore. He cracked bone with stone axes for marrow and cooked his meat which increases nutritive value.
Australipithecus had fur. Homo erectus lost his fur so that he could run faster in day time hunting. Sweating from increasingly numerous sweat glands kept him cool in the hot sun. Long legs increased speed and cooling. Retained hair on head protected skull knocks, beard protected fist fights, pheromones and friction dictated pubic and armpit hair. Fur everywhere else vanished.
Furred creatures have white skin, which is not exposed to sunlight. After losing fur, Homo erectus acquired melanin producing enzymes 1.2 million years ago to protect from ultraviolet damage, which causes skin cancer. For ever after, until very recently, all men and their ancestors were dark skinned for this reason.
Homo erectus evolved into Homo heidelbergensis about 700,000 years ago. Heidelberg man hunted with stone tipped spears and moved out of Africa, replacing and maybe interbreeding with Homo erectus in most of Asia and Europe. In Europe and Siberia, Heidelberg man evolved into Neanderthals and Denisovans. In Africa Heidelberg man evolved and became Homo sapiens around 200,000 years ago. Modern man again spread out of Africa about 70,000 years ago, interbreeding with Neanderthals and Denisovans but ultimately replacing them. 1-3% of humans everywhere except Africa have Neanderthal and Denisovan genes. Some of them might have improved our immunity or increased our tolerance to high altitude. Elsewhere Homo erectus continued to live in small communities and became extinct only 115,000 years ago, at the end of the Eemian period.
It’s important to realise that humans evolved from very small numbers. Neanderthals had permanent long term habitation in Europe from 400,000 years ago, but were not very fertile, never numbering over 50,000 people. Modern man was more fertile and hence replaced Neanderthals despite better adaptation of Neanderthals to the cold weather of Ice Age Europe. By the start of Holocene in 9000 BC Modern Man alone survived, and might have numbered a few hundred thousand individuals all over the world.
DNA from Homo heidelbergensis, Neanderthals and Denisovans have been sequenced. So has archaic human DNA. The results throw up startling findings about skin color.
Homo erectus of Europe was black. Neanderthal man was black. Modern man living in Europe until about 8000 BC was also dark skinned, occasionally with blue eyes. Everywhere in Asia Africa America, humans were varying shades of brown and black. Never white.
Vitamin D production needs light skin and UV light. But folate gets degraded by UV, if skin is too light. Folate is necessary to prevent cancer. The balance between these two, drives the skin color of humans based on amount of sunlight available. People in tropics always evolved towards dark skin to protect against skin cancer and since that’s where H erectus and H sapiens evolved, they were all dark skinned.
Blonde hair evolved around 9000 BC probably starting from small populations in Russia. Pre agricultural human settlements were under stress at this time. The number of men decreased as hunting and scavenging became harder and some didn’t return from hunting. Much of the big mammal herds and predators progressively become extinct with the start of Holocene. Humans from other competing clans were a danger. As the number of women increased, the fewer men selected light skinned blonde haired women as their mate due to sexual selection, affecting the allele frequency. Once derived, the northern climate ensured better survival of light skinned humans due to Vitamin D related selection pressure, but had selection disadvantage at lower latitudes near equator. As agricultural techniques which developed around 7000 BC in the Levant spread west to Europe through the human population, these skin and hair colours spread too, as did the Indo Aryan language group.
Nowadays of course blonde hair comes from a bottle. Anybody can be a blonde, including Indians, removing selection pressure. With less than 2% of the current population having naturally blonde hair genes, within 200 years it is projected to die out. The majority of humans are projected to trend towards a neutral Latin American skin tone.
And as child rearing is undertaken via mobile phone based social networks, time requirements of parenting are reducing. The vestiges of monogamy are likely to vanish very quickly indeed.
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