Humans, and Other Humans

Coursera Course: 
by Dr. Yuval Noah Harari

Personal Lecture Notes from Lesson #1: The Human Family
(These are personal summaries and paraphrasing of some of the materials in the lectures that I felt to be important, with possible additions of personal impressions. They are not meant to be comprehensive records nor intended to be reproductions of copyright materials.)

There is no unbrigdeable gap between history and basic sciences like physics, chemistry and biology. History in the next stage in the process of ongoing complexity in the universe.

Three main revolutions of history:
1) Cognitive Revolution: 70, 000 years ago. Homo sapiens evolved unique cognitive abilities. 
2) Agricultural Revolution: 12, 000 years ago.
3) Scientific Revolution: 500 years ago.

Homo sapiens belong to the Family of great apes. (All the Genera in a Family spring from a common ancestor.) Chimpanzees are our closest relatives, the two species splitting apart just 6 million years ago.
There used to be many other human species (belonging to the genus Homo). Humans first appeared in East Africa, about 2 and a half million years ago, evolving from a genus of apes called Australopithecus (means 'southern ape'). Around 2 million years ago, some of these humans left Africa and settled in various part of North Africa, Middle East, Europe and Asia. Due to different climates and geographical features, these populations began to evolve in different ways leading to different human species.  

In Europe and Middle East, there was Homo neanderthalensis ('man from the Neander valley'; first remains were discovered in Neander valley in Germany). 
On the island of Java in Indonesia evolved Homo soloensis ('man from the Solo Valley').
On Flores, another Indonesian island, evolved Homo floresiensis ('man from Flores island'). Unique thing about Homo floresiensis is that they were dwarfs, having the maximum height of about one meter. 
In Asia evolved Homo erectus ('the upright man', called so because of their height). They were tall, up to 1.9 meters. They are the most successful human species ever in terms of how many years they managed to survive. From about 1.5 million years ago to until about 500,000 years ago, they existed for 1.5 million years (contrast with: Homo sapiens began to evolve around 200,000-300,000 years ago; our prospects of outliving this record are bleak).
From Denisova cave in Russia fossilized remains of a finger were found, whose DNA did not match with any other human species, leading to the inference that there existed another human specie in Central Asia called Homo denisova. 
Meanwhile, evolution of new human species continued in Africa, for instance Homo rudolfensis ('man from Lake Rudolph') and Homo ergaster ('working men'; many tools were found along with their bones). Homo sapiens also appeared in East Africa, around 200,000-300,000 years ago.The world was the home to at least six human species (that we know of) simultaneously. It is surprising, and somewhat suspicious, that there is now only one human species in the world. 

Common characteristics of genus Homo:
1) Large brains, compared to other species (Larger brains, while having their advantages, have disadvantages too. For instance, human brain accounts for 25% of our energy expenditure at rest, while brains of other apes require only 8% of the energy of the body. Large brain needs more fuel, and hence more food intake. This means ancient humans had to spend more time looking for food, compared to other animals. Another toll the larger brain took on the body was that the human body became much less muscular.) It is not obvious that this a good survival strategy. A chimpanzee of 60 kg is five times more stronger than a man of 60 kg. Why the human brain became so large during evolution is a great mystery.

2) All humans walked upright on two legs, freeing the upper limbs, leading to the development of fine musculature of hands. Humans began to construct and use various tools. The manufacture and use of tools is a defining characteristic by which archeologists recognize ancient humans. This led to extra strain on the spine, leading to back aches, stiff necks and various other musculoskeletal problems that we humans so commonly experience. 

Women had to bear extra burden, as upright posture required narrower hips, and therefore narrower birth canals. So while the heads of the babies grew bigger, the birth canal of women grew narrower, creating an obvious problem. This led to greater fatality during childbirth. The evolutionary solution was to give birth earlier and earlier. "Humans so to speak are born prematurely" [lecturer's words]) As humans are born under-developed, they require extra care and attention on part of the parents for survival. This usually cannot be accomplished by a single mother alone. There is a saying that it takes an entire tribe to raise a human child. As a response, humans developed strong social ties with each other. Because humans are born under-developed, it also means during childhood, the eventual development can be significantly influenced by socialization and education. 

For the large part of their evolutionary history, humans were not the top predators, they were rather preyed on. They survived on vegetables, small animals and left overs of bigger animals. Many of the early tools were not for hunting, but rather for breaking open the bones of dead animals to feed on bone marrow, which some researchers believe to be the niche of early humans. Other bigger scavengers like hyenas and jackals left little else of the dead for humans to eat. Only in the last hundred thousand years did humans become top predators on Earth. This is practically overnight in evolutionary terms, and therefore humans are not well-adjusted in this position. Many of our large scale behaviors such as wars and our treatment of the ecosystem are consequences of this over-hasty jump. 

One of the factors important in this jump in food chain status was the domestication of fire. By about 300,000 years ago, some humans were using fire on a daily basis. Fire enabled humans to cook. This opened up immense options of what foods human could ingest, as most foods like wheat and potatoes can not be digested unless they had been cooked. Another advantage is that cooking kills various parasites and germs in the food. It also made chewing and digestion easier for humans, compared to other animals. This led to development of smaller intestines, and because large intestines require immense energy, shorter intestines could've allowed for the development of bigger brains by taking away the competition for energy utilization. 

The real change in the predator status came after the appearance of Homo sapiens. When Homo sapiens arrived in Middle East, most of Eurasia was already populated by other humans. What happened to all the other human species? There are two conflicting theories. 

1) Interbreeding theory: Homo sapiens bred with other human species in Middle East, Europe and Asia, and modern humans are the result of that interbreeding. The only people who are maybe pure Homo sapiens are the Africans.

2) Replacement theory: This theory challenges that different human species had sexual interest in each other, and says that any potential offsprings of interbreeding would have been infertile. This means that all modern humans are pure Homo sapiens.

If the replacement theory is correct, then differences between races are negligible, as all humans have the same genetic package. If inter-breeding theory is correct, then there are possible genetic differences between races. Chinese may have erectus genes and Europeans may have neandethal genes. 

Until recently, replacement theory was more popular, not just because of evidence, but also because of political reasons. This changed in 2010, when the neanderthal genome was published. When compared with our genome, it was discovered that about 4% of genes of Middle Easterners and Europeans have Neanderthal genes. Shortly afterwards it was discovered using DNA from the finger found in Denisova cave that 6% genes of modern Melanesians and aboriginal Australians are actually Denisovan genes. This shows that there was at least some interbreeding between different humans. 4-6% of DNA, however, is not enough to account for a complete merger of populations. It appears that around 50,000 years ago, sapiens, neanderthals and denisovans were at a borderline stage, where they were almost distinct species but still capable of inbreeding on rare occasions. 

How did Neanderthals die out? One possibility is that sapiens out-competed them. If sapiens were more sophisticated than neanderthals in their techniques of hunting, then they would have claimed more and more of the food resources. Another more likely possibility, however, is that this competition was not a peaceful affair. Tolerance is not a human trademark. This may have resulted in 'the first and most successful ethnic cleansing campaign in history'.

The genocides are speculation, but what we do know is that no sooner Homo sapiens arrived in a particular area, the other human species went extinct. The last remains of Homo soloensis in Java are from 50,000 year ago, just when Homo sapiens arrived in Java. Homo denisova went extinct 40,000 years ago, Neanderthals 30,000 years ago, and the dwarfs of Flores island 12,000 years ago. 

Imagine how the modern world would have looked like if Neanderthals still existed. Would Christianity have claimed, for instance, that Jesus died for the sins of all humans or just Homo sapiens? Would American Declaration of Independence have stated that we hold this truth to be self-evident that all members of the genus Homo are created equal? Would Homo sapiens still have believed themselves to be the epitome of creation, separate from the rest of animal kingdom as they do now?


g2 said…
Thanks for the excellent series of posts. I hope you find time to finish the remaining chapters as well :)