EDWARD'S LECTURE NOTES:
More notes at http://tanguay.info/learntracker
C O U R S E 
A Brief History of Humankind
Dr. Yuval Noah Harari, The Hebrew University of Jerusalem
https://www.coursera.org/course/humankind
C O U R S E   L E C T U R E 
Why Did Other Human Species Become Extinct?
Notes taken on August 24, 2013 by Edward Tanguay
the significant revolution in the status of humans in the ecosystem came only after the appearance of our own species, Homo sapiens
appeared between 300,000 and 200,000 years ago in Africa
by 150,000 years ago, East Africa was populated with Homo sapiens which looked much like us
around 70,000 years ago, some of these Homo sapiens left East Africa and reached the Middle East and began spreading over the Eurasian land mass
when these Homo sapiens arrived, most of Eurasia was already populated with other species of humans, e.g. Homo neanderthalensis (Europe), Homo denisova (Siberia), and Homo soloensis (Java), this is one of history's biggest and most important questions: why did these other species of humans become extinct, and what role did Homo sapiens play in their extinction?
THEORY #1: the interbreeding theory
as sapiens spread around the world, they bred with other species and humans today are the result
in Europe: encountered neanderthals
more muscular, better adapted to European climate, had bigger brains, used tools, fire, and good at hunting all kinds of animals
often depicted as brute and stupid cavemen
genetic evidence shows that at least some of the Neanderthals had fair skin
Sapiens and Neanderthals bred and formed a mixture of sapiens and neanderthals resulting in European humans
THEORY #2: the replacement theory
a story of incompatibility and perhaps of genocide
no interbreeding between Sapiens and Neanderthals
different mating habits
different body odors
little sexual interest in each other and children would be infertile
when Neanderthals died out, their genes died with them
sapiens became the last remaining species of human on the earth
this theory suggests that all living humans today are not a mixture but are simply Homo sapiens
in recent decades, this was the common theory
the debate between these two theories is not just an academic, but political of course
70,000 years is not enough time for significant genetic changes to occur
if the replacement theory is correct, this means that all humans living today have the same DNA
would mean that the differences between Africans, Europeans, Chinese are negligible
if the interbreeding theory is correct, then there are differences between human races which go back hundreds of thousands of years
e.g. Chinese might have Homo erectus genes which Africans don't have
this would be political dynamite
2010 Neanderthal genome mapped
from Neanderthal bones
compared this genome to people living nowadays
it turned out that 4% of genes of people living in Europe and the middle east are Neanderthal genes
this means that there are people living today who have ancestors who were Neanderthals and Denisova
also it was shown that 6% of genes of people living in China are Denisovan genes
so the interbreeding area has some truth to it, but it does not mean that the replacement theory is not true
if there were a complete mixture and no replacement then the percentages would be more in the range of 40%-60%
the common theory now is that Homo sapiens intermingled some with other human species but in no way did they merge completely, probably because of the sheer differences between them
big question: were Homo sapiens separate species from the other human species or the same
given the new DNA evidence, it is clear that Homo sapiens and Homo neanderthalensis were not separate species since they were obviously able to produce fertile offspring, however, it would be a mistake to view them as populations of the same species. The truth is that biological reality is not black and white, but complex with important gray areas in the way we catalog and classify animals.
*** the common theory now is that at one point Neanderthals and Sapiens were able to mate and did mate, but they both continued to evolve on separate paths not sharing their subsequent mutations until they became two completely separate species which could no longer mate, this is thought to be about 50,000 years ago
the question still remains: why did Neanderthals vanish?
Theory #1: Neanderthals became extinct because Homo sapiens slowly out-competed them for food
e.g. 40,000 years ago Sapiens from the Middle East arrive in a Balkan valley in modern-day Greece of Bulgaria where Neanderthals have been living for countless generations, these new Sapiens have to eat, they hunt the local deer and eat the local mushrooms, but these are the same animals the Neanderthals live on
Sapiens were already more sophisticated than the Neanderthals and hence Neanderthals were left with less and less food, a few Neanderthals joined and mated with Sapeins which is how 4% of their genes are now in our DNA
Theory #2: Neanderthals became extinct because the competition for food flared up into violence, war and possible genocide
this is quite a likely scenario since tolerance has not been a typical human characteristic throughout history. When you look at human activity throughout history, you can find many instances of intelligence, sophistication, and ingenuity, but examples of wide-spread tolerance is for the most part an extremely recent invention of human beings. Even well into the 20th century, human history is littered with terrible examples in which even small differences in skin color, dialect, or religion has been enough to prompt one group of sapiens to go about exterminating other groups of sapiens. It is highly unlikely, therefore, that an ancient species of human being would be tolerant at all of a completely different human species.
Theory #3: a mix of both of the above two theory: out-competition and targeted violence
one of history's what-if questions: what if many species of humans had survived?
what kind of political and religious structures would have emerged with several human species?
the disappearance of the Neanderthals changed the way Homo Sapiens think about themselves
it's hard for us to conceive that there were other human species and easier to create a gap between humans and the rest of the animal kingdom
when Darwin suggested in the mid-19th century that humans were just another kind of animal, people were outraged
speculation: perhaps this is why Homo sapiens wiped out the other species: they were too similar to ignore but too different to tolerate
what we know for certain: when Homo sapiens arrived at certain places on earth, other species of humans went extinct
Homo soloensis went extinct 50,000 years ago, just as Homo sapiens arrived at the island of Java
Homo denisova went extinct about 41,000 years ago, after Homo sapiens began to spread into Asia
The Neanderthals disappeared about 30,000 years ago, about 10,000 years after Homo sapiens arrived in Europe
The last dwarve humans vanished from Flores island about 12,000 years ago
(by contrast Homo erectus disappeared 143,000 years ago which puts them in a different category, perhaps even the ancestors of Homo neanderthalensis and Homo sapiens)
timeline:
50,000 BC: the various species of humans (Homo sapiens, Homo neanderthalensis, Homo denisova) were at the point where they all went their separate evolutionary ways becoming completely distinct species which could no longer mate to produce fertile offspring
50,000 BC: Sapiens were already quite different from other human species in their cognitive and social abilities