Hi there, I’m Emily Graslie and welcome
to Crash Course Big History. Today, we’ll be discussing human ancestry
and genealogy – important for understanding where we come from and how we relate to each
other today. Looking at the modern science on the topic,
the evidence points toward conclusions that unify humanity into a closely knit family,
reminding us of our common identity. INTRO
Our species, Homo sapiens, came into existence approximately 200,000 to 250,000 years ago,
foraging for generations in East Africa. These early humans were a very small population
with fairly limited genetic diversity. In fact, studies of human mitochondrial DNA,
the small amount of DNA that exists outside of the nucleus of a cell, have concluded that
the ancestry of every human alive today goes back to a single common ancestor from around
this time. Over the next 100,000 years we spread across
Africa, down to the southern Cape, and into West Africa. The low population numbers of human foraging
groups and their relatively disconnected communications with each other, allowed for the genetics
of African foragers to begin diversifying. with population growth over the next several
tens of thousands of years, more connections were made between foraging groups, and human
genetics became more uniform again all over Africa. Let’s go to the Thought Bubble. Around 100,000 years ago, humans moved out
of Africa into the Middle East, and maybe making it as far as India. According to genetic studies, the migration
may have been due to a population boom, as humans got better and better at hunting and
gathering. We can already see collective learning at
work. Then disaster struck. Around 74,000 years ago, the gene pool contracted
significantly and shrank to only about 3,000 to 10,000 people in the entire world. The best explanation we have for this, among
a number of contenders, is the super-eruption that happened around that time at Mount Toba
on the island of Sumatra, in present day Indonesia. It may seem odd that an explosion halfway
around the world afflicted the inhabitants of Africa and the Near East. But Mount Toba exploded with the estimated
force of 1.5 million Hiroshima-sized nuclear bombs. A layer of volcanic ash, an average of 15
cm thick, settled over everything in South and East Asia, but also in India, Arabia,
and as far as East Africa. Much more ash was flung up into the atmosphere,
darkening the skies, and obstructing sunlight, in the middle of what was already an Ice Age. A decade of perpetual winter for the entire
globe followed, with long-lasting effects for centuries. The population appeared to recover quickly
after the weather improved. Over the next 10,000 years there are indications
that humans went through a population boom. In fact, the growth was so great that it is
one of the primary hypotheses for why 64,000 years ago humans made another journey outside
of Africa into our largest mass migration yet. Thanks, Thought Bubble. For a while, migrant humans stuck to warmer
climates, spreading across South and East Asia. In a very short space of time, maybe a few
centuries and at most a few thousand years, humans had colonised everywhere from Pakistan
to Korea, avoiding the chillier continental climates further from the coasts. Approximately 60,000 years ago, humans spread
down the land bridge that existed between Indonesia and the Asian mainland. Through the use of these bridges and perhaps
even seafaring rafts, humans did what no hominine group had ever done before: they landed in
Australia. Eventually humans managed to adapt to colder
climates, spreading into Central Asia and Europe approximately 40,000 years ago. A few thousand years later, we were even living
in Ice Age Siberia. but, we weren’t the first hominine group
to have done all this. In fact, there’s concrete evidence that
humans ran into the now extinct Neanderthals and even interbred with them. Anyone outside of Africa of Eurasian descent,
about 1.5 to 2% of their DNA is of Neanderthal origin. Another thing that no previous hominine had
done was migrate into the Americas. The dominant theory is that humans simply
walked from Asia to the Americas along the Bering Strait, though recent discoveries have
thrown the exact dates into question. but, genetic tests show that humans emigrated
out of Siberia, perhaps hunting animals, and moved into the land-bridge between Russia
and Alaska as early as 30,000 years ago. At this point we would have been prevented
from traveling past the glaciers that blocked us from entering the rest of the Americas. But either by the thaw of those glaciers or
a coastal route, or both, humans spread into the Americas around 13 to 16,000 years ago,
rapidly heading south. But let’s jump backwards a bit. In evolutionary terms, 74,000 years ago is
not long ago at all. And a few thousand people is a tiny gene pool
of relatives. Humans are very closely related for a mammalian
species. When humans left Africa 64,000 years ago,
they left in small foraging bands of a few dozen at a time. It was a decidedly smaller population that
eventually ballooned from all the new resources the rest of the world had to offer. What differences there are between ethnic
groups are pretty small. Certain diseases are more common in some groups
than others, but you see the same pattern occur within individual family histories. Largely superficial and cosmetic traits differ
from region to region. One of the most prominent traits by which
we have historically distinguished human from human is skin color, which is caused by the
melanin levels in our skin. Melanin is useful because it dissipates UV
radiation and helps prevent the occurrence of skin cancer -- particularly useful in areas
with lots of sunshine. 100,000 years ago, every human on the face
of the Earth was African. Melanin levels were roughly the same. And it was only when we spread out into other
regions of the world 64,000 years ago, into different climates, with differing degrees
of UV radiation, did that slowly begin to change. According to genome research, the humans who
arrived in India, East Asia, and Europe between 60,000 and 40,000 years ago had dark skin
tones. And until very recently they retained that
appearance. Specific genes that lead to depigmentation
only became active when humans entered regions where they weren’t getting enough sun and
thus not as much vitamin D. But even this change took thousands upon thousands of years. Researchers have determined, for instance,
that until 8,000 to 10,000 years ago, there were no white people. These ethnic distinctions are blurred even
further by the extreme mobility of different peoples across the ages and especially since
500 years ago, when all the world zones began uniting into a single global system. A great many people have mixed ancestries
as a result. In fact, if you got your genome tested, there
are reasonable odds that your ancestry is pretty diverse too .
It’s worth asking why we’ve had a long tortured history, involving war, murder, slavery,
and genocide over our differences. Plenty of primates, from New and Old World
Monkeys to great apes like Gorillas and Chimpanzees, show hostility toward their own species in
inter-group encounters, arising out of competition for food and mates. For instance, chimpanzees, are known to range
around their territories to find strangers to ambush, mutilate, and sometimes kill. Hostility, fear, wariness, and caution, are
visceral traits that go back millions of years in our evolutionary history. Humans, who aren’t much better except when
we apply logic and reason, distinguished between groups by tribal markers. Humans are good at understanding symbolism,
and here we put it to poor use. Different body paints, dialects, and fashions
in groups that were otherwise ethnically indistinguishable led to great rivalries and generations of
conflict. Once humans started diversifying in appearance,
as languages grew more distinct, as religions became more distant, and as battles for resources
continued, these tribal markers also intensified. From a gut instinct to be wary of strangers,
came the learned behaviour of judging a person by their outward traits. Then came Charles Darwin and the theory of
evolution, a great leap forward. Soon after came the abuse of evolution, which
was a great leap backwards. In the 19th and early 20th centuries, all
the old prejudices found a new explanation, displayed with a thin veneer of scientific
credibility. Darwin’s On the Origin of Species (1859)
made almost no mention of humans. Deliberately. While evolution had the makings for hard science
when applied to different species, when applied hastily to Homo sapiens, it had all the makings
of pseudo-science. On the one hand, until the 1950s and the discovery
of DNA and the synthesis of various parts of Darwinian theory, humans had a very poor
understanding of genetics and how closely related humans really were. A lot the discoveries about our close ancestry
were only uncovered in the second half of the 20th century by more archaeological findings
and the sequencing of the human genome. On the other hand, Natural selection, which
proved revolutionary to biology, was sometimes inappropriately applied to human groups. Differences in behaviour that we ascribe to
cultural learning today were given a biological explanation. For instance, even Darwin in the Descent of
Man (1871) hypothesized that more emotional cultures and more reserved cultures were the
result of inherited traits, rather than just how people are raised to behave in those societies. Some of this was more sinister. Karl Vogt, a German pseudo-scientist, set
out in the 1860s to prove that Africans were a different species from Europeans. Ernst Haeckel in the 1880s put forth a theory
that humans evolved in Asia, not Africa, and that different major ethnic groups had actually
separate primate ancestry, meaning we were divided not by a few thousand years but by
millions and millions of years of evolution. He then talked about superior and inferior
groups. With European imperialism on the rise, pseudo-scientists
grasped toward unsupported theories, cranial measurements, and a whole range of justifications
for their biases. In the 1890s, as competition between Western
empires heated up, figures like Georges Vacher de Lapouge and William Ripley, subdivided
Europeans into different superior and inferior groups as well, this contributed to the intensification
of scientific racism in 20th century Europe, and fed the rise of fascism. This kind of thinking spread all over the
world in the 20th century and some element of scientific racism can be found in the Sino-Japanese
wars, and conflicts in Rwanda, Sudan, and others on a tragically long list. Ignoring our common ancestry continues to
have modern consequences. We humans have been warring for millennia
and it pays to remember the story of our origins and how closely related we actually are, especially
as we move forward as a global society into the trials and tribulations of the 21st century. Just like the Big Bang reminds us of a single
point of origin for all matter and energy in the Universe, linking us together, the
story of humanity reminds us of our common identity. What diversity there is, is cultural. Which I think is something to celebrate. We should specially celebrate the diversity
that is most crucial to human genius and collective learning -- the diversity of thought. See you next time.
