Given the
gradual demographic growth of human beings on Earth, we might think that the
time will come when we will not all fit on the Blue Planet –or we have depleted
all its natural resources–, that we will have to go out to find new spaces
where we can all fit.
But there
have been at least three moments in history when humans have come very close to
extinction.
Photograph
by Joe McNally
1. 1.2 million years ago: humanity before being exclusively Homo sapiens
In 2009,
some scientists analyzed two human genome sequences in search of the most
recent common ancestor (ACMR). Mobile genetic elements are small sequences of
DNA that do not stay in one place; they move and multiply within the genome,
making it easier to replicate these elements than to eliminate them, since once
they are inside a gene they will tend to remain. In this way, the elements
become a kind of trace or record to determine how long ago they were installed
for the first time.
According to
this study:
The genealogy of a genetic region
that contains one or more of these mobile elements is on average older than the
rest. Since genealogies with polymorphic or mobile elements are ancient, they
must have been formed by force majeure events in ancient history, and are
insensitive to recent demographic events, such as expansions and declines in
population.
Thus they
were able to read the history of mankind through genes and, apparently, 1.2
million years ago things were not going well since Homo sapiens , Homo ergaster
and Homo erectus added around the planet a population of just between 18,000
and 26,000 individuals.
This means
that, across the planet, any humanoid species that was able to contribute genes
to a modern-day human was, in total, smaller than the current gorilla
population (considering that gorillas only inhabit one continent and humans
both Africa as Eurasia).
The result was surprising because other evidence indicated that humans were not in danger of extinction at that time, which is known from stone tools found in Turkey 1.2 million years ago. In 2008 a group of archaeologists found the jaw of a human around 30 years of age in Atapuerca, Spain, which indicates that we were scattered, but why so close to extinction?
According to
Chad Huff, co-author of the study, more than an anomaly it was the normal state
of humanity, "either that the population increased exaggeratedly and later
collapsed or that modern humans always formed a small population over millions of
years".
Humans then
may have been what today would be considered an endangered species for most of
their history. The world's small population of humans suggests that the idea of
the species' expansion beyond the African continent, while it may be a correct
observation, is genetically insignificant.
Those
nomadic tool makers may have perished and only the nuclear population that
remained close to home could have contributed to the genetic background.
2. 150 thousand years ago: Homo sapiens and the great cooling
About 195
thousand years ago the world changed, the temperature decreased during winter
and also in summer. Glaciers expanded at the same time that entire habitats
were destroyed. This era is officially called "marine isotope stage
6" (to become known through the analysis of oxygen isotopes settled in the
deep ocean) and is also known as the glacial period or the last Ice Age.
In Africa,
human populations were divided; perhaps this happened intentionally when
certain groups were displaced due to the decrease inhabitable land, but it
could also have happened by chance as habitable space was shrinking. Either
way, the human population suffered heavy casualties. Some believe that the
reproductive population was reduced to only 600 people.
The survivors became both agile and fortunate,
as they were lucky enough to settle by the sea, in what is now South Africa;
that place was particularly rich in plants that stored their energy in the
roots, under the ground; in addition, the water was slightly warm, which
provided a source of food (seafood).
Thanks to
this, humans were able to gather enough food to survive, in addition to
developing ways to help each other. A cave known as the code PP13B near
Pinnacle Point in South Africa shows that the people of that area used the
shells as tools. It is also possible that they tempered their stone tools with
heat, which shows that the behavior of these settlers was more modern than was
admitted.
3. 70
thousand years ago: the Toba catastrophe
About 70,000
years ago, Sumatra blew up, or rather, a supervolcano located on Lake Toba
erupted. According to the Geological Society, a "supereruption"
differs from a common volcanic eruption and other environmental catastrophes
such as earthquakes because "its environmental effects threaten
civilization." Locally, the eruption created a crater that later became
Lake Toba; globally, it spewed so much ash and debris into the air that, by
some estimates, it may have dimmed the sunlight for 6 years.
When this
happened, humans were already in an adverse situation as they suffered from the
dry and cold climate, and now, overwinter years, a noxious gas was spreading in
the atmosphere. Some experts estimate that the population was reduced to
between one and 10 thousand people.
If the Toba
had as much impact as some belief, from one year to the next people saw
themselves in a different world. A pollen analysis before and after the
explosion, from a sample collected in the Bay of Bengal, showed that the
arboreal and wooded flora was replaced by a growth of grasslands, which
represents a drastic change for the ecosystem.
According to
the first theories, humans, rather than surviving, divided, and managed to
subsist. Steven Ambrose, who promotes the theory of the Toba catastrophe, says:
One consequence of the volcanic
winter may have been the rapid differentiation of small migrant populations
originating from the African continent towards what is known as modern human
races. The bottleneck raises a solution to the question: Why do human
populations look so different from each other despite being of African origin?
As the African human diaspora passed through the prism of the volcanic Toba
winter, a rainbow of differences appeared.
Or maybe
not. The Toba theory continues to be debated. While some believe that a series
of bottlenecks transformed humans into today's diverse populations, others
believe that it only meant a brief period of unpleasant years that did not
tangibly change humanity.
The Bay of
Bengal may have been devastated by the blast, but analyzes of samples from Lake
Malawi indicate that the effect on the climate and ecosystem was minimal.
People may have changed and migrated due to a number of climatic, behavioral,
or environmental circumstances, without necessarily being due to the eruption
of the volcano.
