Importance of Natural Resources

CARTA:Climate and Evolution: Rick Potts:Climate Instability and the Evolution of Human Adaptability


– [narrator] This UCSD-TV program is
presented by University of California Television. Like what you learned? Visit
our website or follow us on Facebook and Twitter to keep up with the latest
programs. – We are the paradoxical ape, bipedal,
naked, large-brained, long the master of fire, tools, and language, but still
trying to understand ourselves. Aware that death is inevitable, yet filled with
optimism. We grow up slowly. We hand down knowledge. We empathize and deceive.
We shape the future from our shared understanding of the past. CARTA brings
together experts from diverse disciplines to exchange insights on who we are and how
we got here, an exploration made possible by the generosity of humans like you. – [Potts] There are many fundamental
problems in the study of human evolution, an immense
array of really intriguing questions, in part because the
evolutionary journey has involved an astonishing transformation.
One way of looking at this transformation is through a pairing of slides. I thought
I’d start with the raciest one first but also the most endangering in some ways.
But it poses, this pairing of slides I’m gonna show you, poses a question, and
it’s, how is it that our ancestry included, and in imagined way
in this reconstruction, dilemmas and survival challenges, such as this? And
then in our species that we can present ourselves with a survival challenge like
this. How is that kind of transformation even possible? Ed White’s space walk, the
first human to take a walk in space, how is it, if, in fact, evolutionary process
tethered our species through a change over time, tethered our species to inhuman
possibilities and mentality and society to a particular ancestral habitat and to
particular conditions of life? How can that transformation have taken place?
Another pairing of slides that I think captures this is …can be expressed in
this way. The oldest known stone tool tradition, the old one dating back to
about 2.6 million years ago, and the question that’s posed here is how is our
evolutionary …how is it that our evolutionary journey and technology go
from something like this to something like this?. And as you can read there, this is
space debris that is encircling the Earth. Right there, the entire planet has become
an archaeological sight. And so in many different ways, our species resides on a
human altered planet. Well, in seeking to understand transformation such as this, we
run right up against the fundamental scientific challenge of seeing ourselves
as a phenomenon of nature. And I think that sadly, the folkways in which we see
our species often sees in the science homo sapiens almost as an aberration of nature,
and the dichotomies, the traditional dichotomies, line up in a series of false
oppositions. Human versus nature. Cultural versus natural. Learning versus instance.
Even human versus animal. And it’s especially that ladder dichotomy that
highlights the fosted division that occurs in this particular perspective. Now human
evolution is the period I’ve been looking at so far in this first
several talks, namely the past six or seven million years of Earth’s history,
where the baseline adaptations and the initial possibilities of our species
emerged in ancestors who are no longer around. And so one way to pursue the
question in how the accumulation of adaptations occurred over time is to
examine the environmental context of that entire time period. And so data like this,
which have been shown in the previous two talks, and also is shown on the front of
your programs, is the oxygen isotope curve showing changes and the trends and
fluctuation and ocean temperature and global ice volume. It’s an iconic diagram
of paleo-climatology, and it shows up the past six million years corresponding with
the period of human evolutionary history have been one of the most dramatic periods
of climate oscillation of the Cenozoic era of the past 65 million years. As Peter
deMenocal showed in his talk, paleo-climate records express at least two
signals, the overall trend as well as the variability. And up to about, I would say,
20 years ago, nearly every student in the study of human evolution considered the
variability as simply noise in the all-important trend toward a cooler and
dryer Earth. It was the direction of change, the direction of change, the onset
of grassland dominated savannas, and in East Africa or Africa in general, and of
Ice Age conditions in higher latitudes, that was thought to be the signal, the
signal that elicited the emergence of uniquely human adaptations. Yet all of the
environmental records also show periods of strong instability of amplitude variations
in, as they were switches between arid and moist and between cool and warm. Now among
many factors that have an influence on Earth’s climate system, Earth’s orbital
dynamics certainly are one of them as expressed in this figure. We live on a
spinning planet, who’s axis of rotation is tilted, and therefore, there are
variations, fluctuations in the amount of solar radiation that hits the Earth at
different times of the year and different places on Earth. And so we see these three
variables represented here of eccentricity, the shape of the Earth’s
orbit around the sun, the tilt of the Earth’s axis also varies eccentricity, the
shape of the Earth’s orbit, the first factor, goes from a more circular orbit to
a more oval or elliptical orbit, the tilt of the Earth’s axis of rotation varies,
and also there is this wobble in the Earth’s axis of rotation that relates to a
precision. Well, when you look at African climate, and really climate all over the
globe, but African climate is strongly influenced by variation in solar
insulation. And looking at two major, two of those variables, it’s the interaction
of orbital precision, which have cycles of 19,000 and 23,000 years approximately, an
eccentricity the shape’s of the Earth’s orbit around the sun,
which has periodicities of about 100,000 years and
about 413,000 years. You put those four wavy lines together,
four basically sine curves together, and the interaction of them shows that there
is this interacting …there are these alternating phases of high and low climate
variability in tropical Africa. Peter deMenocal has been instrumental in helping
me to understand this as we got together in a project a number of years ago. And so
what we’ve been able to do, and this is going to come out in the publication soon,
is that we’ve been able to label according to very specific intervals of changes
between the high climate variability times and the low climate variability times of
labeling back through time, back over the last five million years we’ve been able to
do this. The highs and the low. The times of strong instability in East African
climate, where the amplitude of dry and wet were exacerbated or magnified versus
times of greater stability, the low periods. And what we’ve been able to show
is that the times of record that Peter has studied, for example, the dust records as
well as the wet-dry cycles that are recorded in the Mediterranean relating to
eastern and northeast African climate, support this alternation and this pattern
of division between high and low climate variability. Well, the same paper, which
will come out later this year, also explores well, did the places in East
Africa, which where early humans lived, where we find fossils and stone tools, do
those also see fluctuations of this sort? And it turns out that all of the really
prolonged of high climates variability, we see also amplification in landscape
variability in East African sedimentary basins. So for example, this place with
the almost unpronounceable name of Olorgesailie in southern Kenya, where I’ve
been working for the last 30 years, we see that between 350,000 and 50,000 years ago,
which was the high to prolonged tide labeled H2 in the previous diagram, that
time period that we see the landscape changing in amazing ways of down cutting
of the basin and then the basin filling up with sediments compared with earlier in
time. And so we think that these are climate, under climate control, these vast
changes in landscape. And we see this for all of the other prolonged high
variability itervals. Well, I wondered whether in this prolonged high variability
intervals, what happened? Was there anything interesting that happened in
human evolutionary history? And you can see the time scale of five million years
on the left. And what I’ve recorded here are the eight, that is the 25% longest
periods of high climate variability and the numbers that we’ve assigned them in
this paper to come out. And we thought, “Okay, well, what goes on here? What can
we tell from the fossil and archaeological record?” It turns out that almost
everything that’s interesting in African human evolution is concentrated in those
periods of high climate variability. FAD. It’s a strange word, but it just means
first appearance date where a fossil or an archaeological piece of evidence shows us
the beginning of a particular lineage and our evolutionary tree or behavior. And so
for Australopithecus, of all the major genera in our evolutionary tree,
Australopithecus and homo and Paranthropus, are concentrated in a period
of high predicted high climate variability. Also that of homo sapiens at
the top of the chart there. And also the origin of every single major technological
and behavioral transition in human evolutionary history is focused in one of
these prolonged high climate variability intervals. Now one thing that could be
easily criticized about this is that yeah, but new fossils are found all the time and
there are going to be new finds that are made. Well, that happened about a month
and a half ago with a fossil jaw from Ethiopia that repositioned the origin of
the genus homo. Well it turns out that it repositioned it in the next earliest, in
the oldest period of high climate variability. Now I’m not saying that this
is proof, but it’s nice to see a robust predictive model about this relationship
of African human evolutionary history and these periods of high climate variability.
We’see what happens next with the the discoveries. And so we’ve also seen in our
evolutionary tree that we used to have the march of hominids going from ape-like to
human-like, and that gave a sense of inevitability about the existence of
species on Earth. Well, that idea has been completely discarded, and we see that we
are part of a much more diverse evolutionary tree. And in the context of
environmental dynamics, as the conditions of life change with the shifts in
landscape and in food and water and shelter, it makes sense that new
behavioral possibilities, new adaptations and ways of life, were at a premium if
they could allow a greater degree of adjustment in these time periods of very
strong variability in the environment, but this also means, this also means, since
we’re the last bipeds standing, that other ways of life, prior means of existence,
could not be sustained, and they were lost. In the light of environmental
dynamics, we can also inspect this overview of the adaptive history related
to the origin eventually of homo sapiens, and we can now see these adaptations as
the evolution of behavioral flexibility and a wider range, the development of a
wider range of adaptive options and being able to switch strategies, essentially
adaptability in the face of an unstable world. I don’t have time to go through all
of these points certainly, but we can point out few of them. So for example,
things like a simple stone flaking and carrying of food and stones across the
landscape associated with the genus homo, were ways of being able to buffer the
changing menu of food, food distribution and food abundance over time during a high
variability interval. The most rapid rate of increasing brain size relative to body
size. Well, the brain is our organ of plasticity, one of our organs of
plasticity, and that also becomes more understandable, not as something that
evolved in a specific narrow set of environmental and survival conditions, but
in relationship to changing circumstances. Increased cultural diversity and
technological innovation, not, of course, as a characteristic of our own species and
as multiplied the options, the behavioral options within our own species. We also
see in this chart the foundations for a human altered planet, and for example the
changes in technology, control of fire and building of shelters, the …even things
like the moving of complex …moving of resources across the landscape. We can see
in the archaeological record, we’ll talk more about that in a moment, and so what
we see is that we have become very good at surviving by modifying our surroundings,
and that humans, as a result, have spread worldwide, and so thus we have global
change, global transformation of landscapes and the consumption of
resources even founded in this early evolutionary history of human beings. Now
my research team has been working toward the top of this time tree, about 300,000
years ago and very quickly. These are some of the things that were occurring in that
period going back to 280,000 years ago, and remember that’s the time period in
Africa of prolonged high climate variability, and we see the beginning of
innovations. We see increasing innovation, wider social networks, trade, the
beginning of awareness of groups that are distant, far away, that you cannot see,
and yet you’re able to have a sense of values, of valuable rock, like obsidian
rock that was traded over long distance, complex symbolic activity, complex
thinking and planning. And I would see this overall as, in an environmental
context, that we examine now in Africa, a greater capacity to adjust to new
environments. I’m not gonna show you any more than that other than to say that our
research team is about to extend some of these traits even further back in time
prior to 300,000 years ago. And so what we then come up with is that the new theme
and story, the new theme and hallmark of our evolutionary story, is one of
adaptability, increasing adaptability to endure change in the environment, to
thrive in novel environments, to spread the new habitats, to respond in new ways
to the surrounding. And these are the characteristics of the genus homo, and
especially embodied in us, homo sapiens. Final thoughts, the long-term view of
human evolutionary history, the idea of the inevitability of our species has been
discarded, it’s been, I think, increasingly replaced by an emphasis on
adaptability when human evolution is framed within the study of
paleo-environments. And finally, adaptability, according to the definitions
that I just gave, and the demise of ways of life, have been two sides of the
evolutionary process, and I think the question ahead for us, is that this is
evolutionary history, but in the cultural history that is now unfolding, will that
still be the case? Thank you very much.


Reader Comments

  1. 3:18 I think Alexey Leonov might take exception to this statement. I think he's still with us, unlike the unfortunate Ed White who died in the awful Apollo 1 tragedy.

  2. This was a religious polemic. Takes a lot of faith to believe in human evolution. I do not have enough faith to believe this high priest of neo Darwinism.

  3. I see a Wahabbi Christian has commented. I have no faith in religious scam artists who deny science and their sad, deluded minions.

  4. can some one please block this for yankee inbreds, both kinds..the anti and the pro darwin..they are cousins, or worse… lazy…don't have the will to learn and study and work hard at their educations..

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