Natural selection is about the survival of the fittest, but it is not perfect. How can we fix it?
Episode 1 Full Description
Minute By Minute
Section 1
Evolution And Structure
00:00-00:30
Opening Sequence
00:30-02:30
Intro to the episode’s theme
We are in a dark cave. In the background, dripping water can be heard.
A thin, lonely, ray of light is seen, penetrating the deep darkness of the cave.
A little pool has formed at the bottom of the cave.
We zoom in and dive into the pool as the footage turns to animation.
We are looking into a microscope, and unicellular organisms are floating around in 3D.
"In the beginning, there was light. Light is pure and raw information. Information is everything. Since the beginning of life and evolution, living creatures had been positively selected for their ability to harness and decode the information trapped in every photon of light.
While plants can collect and store the energy carried by light, animals can use light to guide their behavior."
Animation: An accelerated evolutionary process from unicellular organisms to plants and animals, culminating in a final image with one single human eye looking directly into the camera.
The image of a human eye fades, and images featuring the eyes of different animals begin to switch one after the other.
They increasingly portray images of eyes from animals that go lower and lower on the evolutionary scale, from birds and mammals, to amphibians, to fish, and ultimately to invertebrates.
"Our eyes are everything but perfect, and our ability to see did not spontaneously come into existence.“
02:30 - 04:00
Intro To Photo-Transduction
We are looking at the night sky through a telescope, while people walk around us.
They look like a bunch of fun astronomy enthusiasts in the middle of a camping ground.
"Science probably started because of pure visual curiosity.
Our ancestors, gathered together around the fire, would probably look up and wonder ‘what are those little lights hanging on from the sky?’
We humans are highly visual creatures, we experience the world, first and foremost, through our eyes. Humans have terrific sight!
We see many colors, and we are not that bad even when it comes to night vision.
But the fact that our eyes are great-and-effective-little-machines doesn't mean they are perfect-little-machines.
They have many crucial limitations".
A pair of hands (the viewer’s) are taking out glasses, handling them from the frame and cleaning the lenses with a piece of cloth.
Animations and footage correspond to what we hear.
"At the center of sight, there is photo-transduction. You see, it's all about translation.
Photo-transduction is the molecular process that happens inside the retina, through which photons are translated into electrical impulses that eventually reach the brain and create an image in our mind.
Photo-transduction is the main player of vision and we’ll make sure we see how this process works, and how it evolved”.
Animation follow the process step by step.
04:00 - 05:00
The making of photo-transduction
Animation: We are walking on a gigantic human retina.
At our feet, the cells that compose the retina are organized in a stereo-typical layered structure.
The first layer is the retinal ganglion cells, the second the bipolar, and the third and final layer is the photoreceptors.
Our feet keep moving forward, stepping ‘slowly and carefully’ on each layer, on each cell, which are named and identified.
“In our first station, on the inner most parts of the retina, we meet the retinal ganglion cells, the first cells in line, and the last cells that respond to light.
We will meet them again later.
As we move further out, we walk on top of a sea of ‘dendrites’ and ‘neurites’, cell projections that work like little antennas connecting cells between themselves.
Here, electrical and chemical communication takes place.
Even though it looks chaotic the flow of information is tightly regulated and controlled.
Now we step on the next layer that is full of small round cells with two projections.
As we can see, each one is expanding in opposite direction. These are the bipolar cells. We now reach the outer most layer in the retina, which is paradoxically the layer that reacts to light first.
We can now see the photoreceptors that convert light to electricity.
These are the makers of photo-transduction”.
We now see photons traveling inside the eye, through the layers we just ‘stepped‘ on, eventually hitting ‘rods’ and ‘cones’ (the two types of photoreceptor cells).
Now we are the photon itself, for which a molecule of ‘rhodopsin’ looks like Mount Everest to a human being.
“Rhodopsin is the molecule responsible for photo-transduction, once a photon hits it, the molecule changes its structure and triggers a cellular response.”
We see the reaction of rhodopsin to light and the molecular chain of events. We zoom out from the level of a single photon hitting one molecule of rhodopsin, all the way to the whole rod cell, where we are still standing.
The change in voltage (caused by the photon hitting the cell) is visible on the membrane and it makes the rod cell shake.
We hear a detailed description of the process of photo-transduction, in sync with the animation and the archive footage of rod cells in-vitro through a microscope in a lab.
Rhodopsin
05:00 - 06:00
Retinal Sensitivity And Detection Of Photons
The microscope seen at the end of the previous sequence, is situated in the lab of Prof. Edward Pugh, from the University of California at Davis (CA, USA).
We tour the lab. Info-Graphics describe the different parts of the lab and its components.
Prof. Pugh, with the aid of animations and microscopy imaging describes the process of photo-transduction and how sensitive photoreceptors are to light:
“We need to understand one critical issue: our retinas are capable of detecting one single photon of light.
Photons are subatomic packages of energy that flood our universe and our world. For any known living organism, the detection of a photon and the reaction to it, constitutes the smallest type of stimulus in existence.
In other words, being able to detect a single photon, like our retinas do, represent the limit of perception and consciousness as we know it.
Any biological response requires a minimal amount of stimulus – we call it ’the response threshold‘.
In the retina, one single photon can trigger a response, meaning this is the only biological response that has no threshold.
In other words, vision is so crucial to our survival, that evolution erased the need for a threshold. If this happened with other senses, like hearing or smelling, our senses will be overloaded in an instance.
The reason this does not happen to us is because the retina processes the signals created by photons, before these signals move on to the brain.”
6:00 – 7:00
Processing Of Information In The Retina After Photo-transduction
We are in an open savannah-like field (Serengeti style) next to a cheetah stalking its prey.
The animation recreates the vision of the cheetah looking at herbivores, choosing a prey to attack.
However, the function of the retina goes far beyond distinguishing between light and dark, day and night. Big animals create complex images of the natural world in their brains, thanks to the intricate processes that take place in other regions of the retina, areas that have been misplaced by evolution”. We go back to walking on the giant retina. Electrical impulses go back and forth inside the retina at our feet. We point to a special type of cell. “These cells, for example, react to the light moving in a specific direction.” We point elsewhere, “and this type of cell reacts only to dim light, while this one reacts only to strong levels of light”. We listen to how we process "light and dark adaptation‟, "motion sensitivity‟, and "lateral inhibition‟. “These intricate abilities of the retina take place in-spite of the fact that the structure of the retina is a big continuum of evolutionary mistakes. Our retinas are in fact upside-down.”
We go back to walking on a giant retina
07:00 – 08:00
Retinal Structure: Evolutionary Mistakes
We are in a dark room with a single ray of light from an unseen source. Suddenly, light shines on a wall to uncover a framed picture (like a piece of art in a museum). It is an expanded microscopy image of the retina of a fly. Next to it, a light turns on over a new picture, is the retina of an octopus.
Then a framed picture with the retina of a fish.
Then a turtle, a frog, a bird, a cat, then a primate and then a human one.
We even adopt their point of view: we now see like a fish, an octopus, a fly…
"From the simple task of detecting light, retinas evolved to do much more: measuring the intensity of the light, identifying millions of different colors, adapting to changing contrasts and shape, tracking a moving object, activating our circadian rhythms. To achieve this, evolution resulted in the generation of new and specialized cells in the retina. These cells take the information created by the photoreceptors and integrate it into a multi-layered response that travels back to the occipital lobe of the brain. These are the bipolar cells and the retinal ganglion cells, and the melanopsin cells. The more living creatures benefitted from seeing the light, the more they were selected by nature to absorb more light-encoded information. And so, layer after layer, the retina evolved to add more calculations, more computing power. The photoreceptors were left behind, in the outer most layer, far from light, while the accessory cells came in later and closer to the light.”
We now view The Museum of Retinas, featuring the human retina.
08:00 – 9:00
Evolution And Retinal Structure
Prof. Helga Kolb from the School of Medicine, University of Utah, talks of the comparative anatomy of the retina across species.
Animations and footage are presenting the evolution and the human retina, while emphasizing the limitations of human sight: detectable wavelengths, optics, and photo-transduction – the three most important topics discussed at length in the following Section 2.
09:00 – 10:00
Summary Of Evolutionary Mistakes
We are back in the museum of retinas, recounting the different limitations of our retinas and our eyes at large (field of view, eye movement, position and clarity of the lens, position of the retina, pupillary reflex limitations, etc.).
The giant retina is at our feet as we face the museum of retinas.
"Our retinas, and indeed our sight, is limited in many ways.
Because evolution works by trial and error - what works is selected for, and remains. But the fact that something works does not mean it's perfect.
Which means… that it can always be improved.
How would engineers re-invent photo-transduction and sight, if they could?“
