The Secret of the Human Eyes: How Evolution Shapes our Perceptions

 

 

This post is reproduced from my blog "The Proud Holobionts" where I explore how the new concept of "Holobiont" can find applications not only in biology, but in many fields dealing with complex systems, including the human economy, memetics, and ecosystems

 

 

The short movie abov, Vikaari, has recently appeared on the "Dust" site and I think has several interesting features, relevant to the concept of holobionts. 

 

It is very well done as a movie, although it is deeply contradictory in many aspects. For one thing, it is a narrative disaster. First, the movie tells you that the "Vikaari", children born without a visible iris in the eyes, are good people, while being the target of Nazi-like bad guys. Then, we see the Vikaari killing their pursuers using their psychokinetic powers in bloody and cruel ways, apparently without any regret. Needless to say, this completely destroys the narrative tension of the movie and leaves you totally baffled about what the filmmakers wanted to say.

Indeed, I think the filmmakers were badly confused on several planes. First of all, in their decision of presenting this "new race" of children as something that will replace current human beings, engaged in destroying their own planet. Is this a hope or a fear? Difficult to say, but surely evolution doesn't work in that way. 

And then, why the choice of iris-less eyes as a defining mark? It is rare that people consciously perceive the characteristics of the irises of their fellow human beings. But the shape of the iris tells us much of the genetic inheritance of a person. On this point, the film-makers got it right, although in reverse. A human being without a visible iris is not a modern human.

 

The iris is an easily modified, highly visible human trait. There is a whole genetic story in the human iris. From what we can say, light-colored eyes have been rare in the remote past, although DNA studies indicate that they already existed in the Mesolithic period. Curiously, Europe is the continent where, nowadays, light-colored eyes are most common. But it is only a few centuries ago that light-colored irises start to appear in paintings. If they had existed before, surely painters would have noted them and shown them in their paintings. Green eyes are a modern trait in Europe, they seem to come from Northern Asia. They do spread easily because they are a typical "epigamic" trait. They give a certain advantage in the sexual competition for mates. 

 

And then, there are limbal rings. The dark ring that surrounds the iris. Also a typical epigamic signal, they are likely to be a feature of the modern main organism of the human holobionts. Here you see the eyes of Sarah Brightman, a modern human specimen. Note the light green color and well detectable limbal rings. As epigamic signals go, Ms. Brightman is surely beaming them out loud and clear!

 

Note the difference from other mammalian eyes. Most animals, even our close relatives, the apes, have dark eyes, no limbal rings, and not even a large and well detectable sclera. You see it in the image: this (probably) female bonobo doesn't look at all like Sarah Brightman, although she also surely sends powerful epigamic signals to the males of her species. 

So, why do the Vikaari of the movie have no irises and no pupil? They are, actually, the specular version of the "black eyed people," characters of a recent horror movie. In both cases, filmmakers understood that the lack of sclera or of the iris is a characteristic of a creature that is not fully human. A new species (as in Vikaari) or an otherworldly evil creature (as in "Black Eyed Creatures"). No wonder that regular humans react with great perplexity and sometimes violently to these alien-looking creatures. And this violence is reciprocated in Vikaari. 

The existence of these films shows our limited understanding, and also limited tolerance, of what makes humans human. A small difference in the extent of the sclera or in the color of the iris is sufficient to turn otherwise fully human creatures into enemies, at least in these fiction pieces. But we all know very well that it happens also in the real world for other, no more important genetic traits, such as skin color. 

 

There is a thin line that separates the horrible from the attractive: nobody would be killed for having green eyes, but the white-eyed Vikaari could be if they existed for real. But that's the way evolution works. Sometimes gradually, sometimes in bumps. The human holobiont of the future will not be the same as it is now and it was in the past. It is the giant holobiont that we call the ecosphere that changes all the time. Onward, fellow holobionts!

Finally, for your curiosity, the "Statue of a Standing Nude Goddess," presently at the Louvre Museum and coming from excavations in the Middle East. Note the eyes without irises. It is not clear if that was a bug or a feature: once they had decided to use rubies for the eyes of this statuette, there was no way they could have shown irises and pupils. But maybe it was intentional: this figure may have been supposed to be somewhat otherworldly or even threatening. Note the horns on her head, a typical attribute of the Moon Goddess. Already at the time when it was made, probably the 2nd century CE, goddesses were rather unpopular and suspicious, not unlike our modern witches. 

Gaia Exists! Here is the Proof

Gaia is neither benevolent nor merciful. She is harsh and ruthless. 

Environmentalists are sometimes defined as "Gaia worshippers," a term supposed to be an insult. That's a little strange because most people on this planet openly worship non-existing entities and that doesn't normally make them targets for insults. Maybe it is because there is an important difference: Gaia exists.

But who or what is Gaia, exactly? The name belongs to an ancient Goddess but the modern version is something different. As you probably know, the term was proposed for the first time by James Lovelock in 1972 and co-developed with Lynn Margulis. As it happens for many innovative ideas, it was the result of a simple observation: if the Sun radiative intensity increases gradually over the eons, how come that the Earth's surface temperature has remained within the boundaries necessary to keep the biosphere alive? There has to be something that keeps it like that. Lovelock proposed that the mechanism was based on regulating the concentration of greenhouse gases, mainly CO2. You understand that this idea goes at the core of the current debate on climate change: it deals with the inner mechanisms that make the Earth's climate what it is and what it may become in the future.

So, Gaia is powerful but She is not supposed to be benevolent or merciful, and not even a Goddess: we could say that She is what She is. But does She really exist? Not everyone agrees on this point. The concept is often referred to as the "Gaia hypothesis" and entire books have been written to demonstrate that there is no such a thing as a control mechanism of the Earth's temperature. Indeed, in the beginning, the idea was mostly qualitative and not proven. Lovelock proposed a clever model called "Daisyworld" that showed how a simple biosphere could control the temperature of a planet. But the Earth's biosphere is not just made out of daisies and something more than that was needed. But over time proofs have accumulated to show that Gaia is much more than a qualitative hypothesis (or an object of worship by people believing in non-existing beings).

Let me show you some data from a 2017 paper by Foster, Royer, and Lunt that can be seen as proof of the existence of Gaia even though they never mention the term. It is not about new discoveries, but it uses available data to look at how the concentration of CO2 and the sun irradiation varied over the past 400 million years, most of the eon we call the "Phanerozoic." The paper is somewhat technical, but clearly written and you can follow the argument even if you are not a specialist in atmospheric physics. Here are the main results:

The top (a) figure shows the average CO2 forcing (red line), compared to the solar forcing (yellow line). "Forcing" means the thermal effect over the Earth expressed as power per square meter (W/m2). It is called forcing because it is a change of a previous condition. A positive forcing warms the Earth, a negative forcing cools it. Values of the order of a few W/m2 may seem to be small, but they may change the Earth temperature of some degrees C.

The surprising result shown in the figure is how the two forcings, sun and CO2, balance each other nearly exactly. You can see that in the bottom panel of the figure: the net forcing is the red line. This is truly impressive. Assuming a sensitivity factor of 0.3, you can calculate that the solar forcing, alone, should have increased the Earth's average temperature of about 2-3 C (nearly 5 F) over 400 million years. The increase would have been considerably larger if feedbacks (e.g. water vapor) are taken into account. But we don't see this increase, not at all. Here are some recent data by Mills et al.

Look at the gray curve: plenty of oscillations but, on the average, the temperature has remained constant over the past 400 million years. If it had increased even of just 2-3 degrees C, the effect would be clearly detectable. If we push back the boundary to more ancient times, to the origins of life on Earth, the effect should have been much larger: the ancient Earth should have been at least 20 K colder than it is today. It should have been a ball of ice. It was not: we know that there was liquid water even in those remote times.

So, the data are clear: the increasing sun irradiance over the Earth's geological history has been compensated mainly by a declining CO2 concentration. Of course, there are other factors affecting climate: other greenhouse gases, changes of albedo, ocean currents, clouds, atmospheric particulate, orbital and axial oscillations. But they seem to play a minor role at the time scale of an eon. And would you believe that this near-perfect compensation occurred by chance? Yes, sometimes things happen by chance, but can the same thing keep happening by chance for 400 million years?

Anyone said "Gaia"? Smile! The Lady is right in front of you. She exists and we are lucky that She is what She is. Otherwise, the biosphere wouldn't have died long ago, burned or frozen.

But what mechanism causes the CO2 concentration to decline as solar irradiance increases? And where does the removed CO2 go? Lovelock had proposed that it was just the biosphere that did the job, it seems now that we need a tight coupling of biosphere and geosphere to obtain the effect we see. In part, CO2 is removed from the atmosphere by photosynthesis and then transformed into the inert substance called "kerogen" (the precursor of fossil fuels), then buried into the crust. In part, CO2 reacts with silicates in the crust to form solid carbonates. It is a long story and not everything is known, but things start to make sense. Lovelock was right.

Now, are events occurring over hundreds of millions of years relevant for us? Absolutely yes. The time scale may change, but the physics remains the same. The impressive point is that there is no fiddling, here, with mysterious models. These are experimental data coupled with simple physical principles that have been known and established for at least a century. They do show that CO2 affects climate, something that many non-worshippers of Gaia refuse to accept.

Comparing the current situation with the record of the Phanerozoic, we can see that the forcing that we are creating with our CO2 emissions (at present about 3 W/m2, and rising) is of the same order of magnitude of the past forcings that caused the Earth to reach the condition of "hothouse Earth," 10-20 degrees warmer than it is today -- and that even for a smaller sun irradiation! If it has happened in the past, it may well happen again. But it would be easier today because the sun is hotter. So, we may well be in deep, deep trouble.

How fast could the transition to hothouse Earth happen? On this point, the Phanerozoic data help us little: we don't have the resolution that would be necessary to detect rapid events such as the incredible burst in atmospheric CO2 concentrations that humans have created during the past few centuries. Some people say that humans will go exctinct in a few decades because of the triggering of the release of methane, another powerful greenhouse gas, from the permafrost. That would be consistent with the several mass extinctions that took place during the Phanerozoic: we know that Gaia is neither benevolent nor merciful.

But the extinction of humankind is not necessarily Gaia's will. The damage we made may still be reversed, especially if we manage to crash the global economic system. That would stop the burning of fossil fuels and the Earth might return to the previous conditions without the utter destruction that some scenarios foresee. Eventually, it surely will, even though that may take a few million years. Gaia may not be benevolent, but she is surely patient.




You Gotta Believe from Nina Paley on Vimeo.



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A comment from my personal troll

Ancient kings hired personal advisors to remind them that they were mortal. This I know well enough by myself, but I thought I could hire a personal troll to remind me of my limits as a scientist. Here is a comment from him, Mr. Kunning-Druger). 

Glad to see this post, professor Bardi, and I see that you and your friends finally admitted what you always refused to admit: climate has always been changing. And all the data you are showing to us that humans have no effect on climate: look at all those variations in CO2 concentrations: where were the SUVs, the coal mines, the oil wells that you and the others have been telling us are the cause of "climate change"? How can that be? And the supposed "coincidence" that you are showing to us, that should "prove" that Gaia exists. Do you think we are stupid to believe that when we know that these numbers come from the same people who wrote "hide the decline" in one of their mails? And all this story of the Goddess, again, it proves what we had been saying all along: those idiotic Greens are just a bunch of adhorers of Nature, they and their little prophetess, that disturbed girl, Greta - just another scam among the many. You think you are doing science, but you do politics with just an attempt to mask it with a little New Age flavor. The reality is that the whole story is a scam to get public money for your fat research grants. We know that and I am going to write to the president of your university to tell him that you are wasting the salary that the government gives to you. You are using it to scam people and you should be fired together with all those silly scientists. (KD).