Timelines

1. 13.5B years ago - Big Bang, time, energy and space came into existence. These building blocks of the universe came to be known as Physics. 300,000 years after that, mattered appeared. Atoms emerged and clustered into molecules. The basic building block of matter is called Chemistry.
2. 3.8B years ago - Earth came into being and organisms flourished. The study of these living organisms is called Biology.
3. 70,000 years ago - Homo Sapiens (man) developed culture. A chronological array of cultures is called History. Man's Cognitive Revolution took place. History is shaped by 3 revolutions - cognitive, agricultural and scientific
4. 12,000 years ago - the Agricultural Revolution transpired
5. 500 years ago to present - the Scientific Revolution began

Nothing Special
Humans have been around since 2 million years ago. They were gathered in clans, loved, laughed and competed for power and status. But so did the other primates and animals. There was nothing special about man during this time.

Species
Beings who can mate and produce an offspring that can in turn reproduce, belong to the same species. A Chinese and African, although differing in color and looks can produce a viable offspring. They both belong to the same species.

Genus
A horse and donkey belong to different species. They can mate and produce an offspring, the mule, but it will be sterile. But the horse and donkey both came from a common ancestor. This means they both belong to the same genus, but not from the same species. Lions, tigers and the big cats all come from the same genus, Panthera. Biologists pair the genus-species. For humans, we are Homo (genus, man) Sapiens (species, Wise Man).

Family
This is the upper grouping of genus. Us, Homo Sapiens, falls under the Family of Big Apes - chimpanzees, gorillas and orang-utans. 6 million years ago, chimpanzees and humans had the same mother.

Closet Secrets
Humans belonging to a grid of animals used to be contentious since religion wanted to categorize Man as special - of divine origin. But that has long been disproven. In fact, Man, is not the only species under Homo. We have genetic siblings. Human or Homo refers to us and the Neanderthals, Denisovans, etc.

Humans (not us, but Homo) wandered to different parts of the world and began adapting to different environments. Scientists gave them different species names.

Humans: Homo rudolfensis (East Africa), Homo erectus (East Asia, ‘Upright Man'), and Homo neanderthalensis (Europe & western Asia, Neanderthals)

Homo erectus survived a long 2 million years, the most durable of all humans. Us, Sapiens, will probably won't be around in the next 1000 years, So 2M years is very long (so, why did they go extinct?).

Homo oresiensis
It's interesting to note that in a tiny island in Indonesia, a meter-tall human flourished. When food became scarce, the bigger guys died off. The surviving smaller guys mated and over the generations, they became dwarves.

Homo denisova (Denisovans)
In 2010, in the Denisova Cave in Siberia, a fossilized finger bone was discovered. It belonged to a species previously unknown. This brings the question, how many humans roamed the planet we don't know about?

Linear Lineage?
It is common thinking that there was only one type of Homo (human) in existence which evolved until it became Sapiens(us). That is not true. From 2M to 10K years ago, there were many Homo species roaming the earth - some were massive and roamed the planet while others trapped on a small island were miniscule and subsisted on plants. But all the other human species died out leaving us the only surviving species of the Homo genus.

Brain Drain
Humans have the largest brain of all animals but our brains take up 25% of our energy while at rest even though its weight is only 3% of body weight. The brain uses a lot of energy so we had to spend more time looking for food. It came at a cost. Because the trajectory is growing newrons, our muscles atrofied. So, how did we survive with weak muscles? No one knows. But this big brain allowed us to pierce the atom and send people into space (although this is a very recent occurence).

Standing Upright and Finger Dexterity
Humans eventually learned to stand up, freeing their arms for other tasks, and therefore developed more dexterity over time. This also meants back aches and stiff necks for our heavier cranial feature.

Premature Sapiens
Unlike other animals who are on their own when born, Sapiens are helpless. They have to be nursed, protected and looked after. This is not easy for a lone mother. The village had to help out - thus the galvanizing of the tribe to raise a human. This is an important feature of the human social structure.

Born premature also means we can form and shape the baby's thinking. We can make it grow to be a Christian or Muslim, etc.

Super Sapiens?
With big brains, ability to make tools, sophisticated social structures, humans should be on top of the food chain. But no. For the first 2M years, they were not special. They remained in the middle of the food chain, wary of bigger predators. It is speculated that eating the bone marrow of animal carcass (when everyone else has done their picking), led to our progressive evolution. It was not until about 100K years ago, with the emergence of Sapiens (us) 150K years ago, that Homo came to leap frog the food chain. We came on top too fast that the ecology couldn't adjust fast enough. How did man go so fast on top of the food chain?

Fire
Humans learned to use fire on a daily basis as early as 300,000 years ago. With fire, they could cook their food, be warm and protect themselves against predators. With cooked food, digestion became easier and faster, resulting in shorter intestines, smaller jaws and little teeth. Easy chewing left more energy for brain expansion. With fire came power and more opportunities.

What Happened to the other humans?
About 70K years ago, Sapiens arrived in Arabia which was already populated by other humans. What happened to them?

Plight of Homo sapiens from East Africa

1. Interbreeding Theory - Sapiens mated with other humans and the offsprings are now us. In 2010 geneticists found that our human DNA has about 3% Neanderthal and 6% Denisovan DNA. But how can 2 different species mate and produce fertile offsprings? This means that Africans, Chinese and Europeans have genetic differences - this is very volatile in this era and explosive. If 2 species recently branched off the genus, they may still produce fertile offsprings, albeit rare. It would seem that 50K years ago, Sapiens, Denisovans and Neanderthals were at that evolutionary fork where their offsprings are still fertile.
2. Replacement Theory - Sapiens didn't look like the other Homo and didn't want to breed with them. Since they were viewed as competition, there was genocide with Sapiens winning the war. Or, the Sapiens drifted into Neanderthal territory and being more intelligent, consumed their resources leaving the Neanderthals to die out.

Neanderthal child

Humans Dying Out
When the Sapiens encrouched on another human territory, the other humans invariably died out, eventually leaving Sapiens to be the only surviving species of the Homo genus. What if they didn't die out? What if they co-existed with us today in modern society? How would society be different? Would it open up a new class structure? If racism exists where it's the same species, how would it be if it's not even Sapiens? What kind of racial divide would it entail?

How could they have all died out? Language?