Evolution of the Eye by Dan E. Nilsson

my name is Dan Nilson and I'm a professor of biology at Lund University and I work on vision in animals really all sorts of animals from jellyfish to man and I'm gonna give you a lecture today about the evolution of vision the title says evolution of the eye as if I just meant the human eye but that's not really what I meant mean I mean the evolution of eyes in general so good evening everyone and welcome to the third of the 2019 Darwin College lectures on the theme of vision last week if you were here you have heard a Nia Herbert speak on vision and color and she showed how subjective our interpretation of color can be that what we think we see may or may not be correct or even there and how many factors can affect how we visualize color so eyes the creationists question is of what use is half an eye and Charles Darwin thought about that of course now eyes are wonderful things in my own research I've worked on the mid-ocean ridges where the tectonic plates diverge many of the life forms along these deep-sea ridges are endemic and only found in those extreme chemical temperature and pressure environments basically around the hydrothermal vents the hot water springs there in the Atlantic shrimps swarm around the hydrothermal vent chimneys and feed on chemosynthetic bacteria now Cindy van Dover discovered that these shrimps have evolved the most remarkable eyes they're located on their backs and are essentially just naked retinas adapted for detecting the radiation from the vents this hot very hot water remember there is no sunlight two or three kilometres down in the ocean so the topic of tonight's lecture would I think delight Charles Darwin the topic is the evolution of the eye so please welcome professor Dan Eric Nielsen from the department of biology at Lund University in Sweden to speak to us [Applause] it's a pleasure and an honor to be here give this lecture actually had there not been an evolution of the I you wouldn't have found your way to this lecture and I probably wouldn't be here to lecture about it either so it's because of the evolution of the eye that we're all here I'll try to give you some idea of why when and how eyes evolved it's been some controversy about its long time ago starting with down of course but also in more recent decades but nowadays I would say there is not much controversy left we pretty well understand how eyes evolved why they evolved when they vote and that's what I'm going to talk about so we'll try to bring more clarity to the question of course the eye is not really it the eye is a complex organ it contains many different parts and that was the original problem to try to understand how you can get that many parts at the same time you don't really need to have them at the same time they'll turn now we've come to that pretty soon but I will actually not start to try to simplify things I'll start to make a mess instead by complicating things because the title was actually not really the intended title the title says evolution of the eye kind of implying there was a sky that I was going to talk about human eyes that would be just the small part of this story so the talk is really about the evolution of eyes and then we need to see what kind of ice there are we have we have vertebrates ourselves and we share eyes that are very similar to us with other mammals with birds reptiles amphibians and fish that's actually officiate so as you can see on the blue spot it's a blue spotted ray even though it looks like a frog but the frog is actually over there we've got other animals that's not a vertebrate I that's actually a cephalopod I it's a squid I very similar in general design to ours but if you look at the details they are very different there are spiders that's a little jumping spider it's got beautiful eyes we've got insects with their compound eyes there are many different types of compound eyes even their crustaceans also share compound eyes also many different types do you know what kind of animal that is nothing you see around every day it's a I can see a friend of mine over there he's got just manian wife they are from the southern hemisphere it's a velvet worm they've got tiny little eyes but it's a little lens and everything is there that's a gastropod gastropod mollusc a conch doesn't seem to really understand why it's got its eyes it seems that's a rag worm it's got two pairs of eyes on its head and that's a flatworm it's got a pair of really really simple eyes but it's actually even more complex than that this lizard has got a third eye in the middle of its head this is a bee like other insects they've got an extra set of not compound eyes but single lens eyes in the middle of their head this is a marine flatworm it's got a compound eye single compound eye in the middle of the head if they have a hit jellyfish don't have definitely don't have a hit but they still have eyes these are eyes of over jellyfish box jellyfish these eyes the little blueberries there on the scallop that's actually eyes long row of eyes but not on the head that's actually sitting on the part of the the mollusk that is called the mantle the part that generates the shell now producing heaps of eyes yeah a relative to scallops that's the same part the mantle of the urban art clan there are lots of compound eyes along there yeah that's the tentacle of a sedentary worm sedentary over the fan well on the tip of the tentacle it's not really their normal eyes on the head they've developed little compound eyes yeah that's a compound eye at the tip of the arm of a starfish this animal has a vision sea urchins have vision but they haven't really got in the eyes instead they've got light receptors small light-sensitive cells sprinkled across the skin and looking through actually between the spines so the whole animal works like if it was a compound eye tightens also have dispersed vision numerous little black dots here are actually little photoreceptors arise so they combine the information of all these to respond to their environment so this is a more complex picture of the eyes we know of today all sorts of ice in various parts on the head and back basically on any other part of the body and if you ask could you remove any parts of these eyes and the system would still work most often you would know actually if you remove this and that the system wouldn't work anymore but there is one thing that you could make any use of if you ask the question is there what kind of thing could be useful in these eyes if you removed everything else the only answer to that is the light-sensitive cells you could actually make use of light-sensitive cells if you had nothing else and lots of animals do that because all animals all animal eyes and light sensitivity is based on the same molecule or the same it's actually vitamin a of different types of vitamin A and that is a really clever molecule because when it receives light it changes conformation and you can easily flick it back yeah through an enzyme or even by using light again you can flick the ant so you can reuse the molecule over and over again it's a really really useful molecule for for detecting light em it sits in a receptor protein which is called an opsin and all animals use have their vision based on options in the option you find a little vitamin A molecule and the option is responsible for four actually set starting the events in the cell that leads to a nerve impulse due to an electrical impulse but if we take a closer look at these options because it turns out there is not just one option that all animals share there is a whole group of different options or actually its whole family or class of options there are many different subgroups which will remain or return to laters see options you should remember and are options which are important and there is another group often referred to as Tet rope since and there is actually a handful of other groups which is not even in this diagram one important thing we should notice that the closest relative to all these options is actually melatonin receptors because opsins are part of this large family of receptor molecules that we use for taste for olfaction for smell for for neural transmission and for whom our communication in the body so it's huge family of receptor proteins just the small part are the options and the closest relative is melatonin receptors you know melatonin that's the hormone in our sleep human that tells us it's night and we should go to sleep it turns out that melatonin itself the molecule melatonin that the receptor is sensitive to could actually be a light receptor and it is a light receptor it seems in some single-cell organisms because it is light sensitive if shine light on melatonin it oxidizes and it no longer fits the receptor molecule so if you have a constant production of melatonin and at night you will build up large level or high levels of it and you will be able to know it's dark as soon as day breaks light will reduce or actually not reduce he'll oxidize the melatonin and make it ineffective so that it's quite possible that that was the precursor of all visual events in all animals but it's a kind of useless male like molecule anyway because it is sensitive sensitive mainly told to violet which is it's hard to make it sensitive into the into the visible and also you kind of ruin it by shining a light on it you have to produce new melatonin all the time the vitamin a molecule is far better because you can change the conformation of it and reuse the same molecule so by just modifying the protein a bit such that it works with with vitamin A rather than with melatonin that might have been an early and really good change that made all visible possible made all vision possible take a look again at this cluster different ops in groups the interesting thing is that these groups contain options from all major groups of animals so all major groups of animals share every type of ops in which means that our earliest ancestors before they actually branched into the different animal groups must have had all these types of options knowing that we can try to turn the clock back and see when we can actually time and work out when this might have happened if we look at another type of phylogenetic trees namely those of animals so these are all the animals we've got sponges down there jellyfish appear insects various kinds of mollusks and and other invertebrates of starfish up there and our relatives up in that corner and now this whole thing is time so we've got a timescale on it and sponges they don't have any options at all all the other groups have all the different types so then we can just fall out here and see it's between roughly there from around 700 million years ago now this graph is actually not the newest one so people keep reached or changing the dating of animal phylogeny so these things would now be closer to 800 million years ago than to 700 million years ago I don't know about these things but I trust people that make these dated trees so that's a long time ago then that opsins appeared so opsins must have appeared after that time and all animals would have acquired the four different or possibly five or six or seven different types of classes or options shortly after so we know roughly when that happens but that is only opposite what can you do if you just have an opsin you can express it in some sense results up since they opsins reside in membranes they're all these receptor proteins of membrane bound so if you pack lots of options in your membrane you can make a cell that is sensitive to light and so what what might you have such a thing Forge could it tell you it'll affirm inform you about the ambient intensity which tells you if it's night or day of course you can use it for knowing about lunar rhythms or yearly rhythms you can actually also use it for UV warning for to high levels of ultraviolet radiation which is harmful you could use it as a shade detector you could use it as a depth gauge which might have been really important reason for the these early up since the deep you are in the sea the less light there so you could regulate your depth if you just measure light if you're living in them in sand or gravel wring them out in the sea floor you can if you're borrowing there you could use it to determine when you actually break the surface or a close to breaking the surface so there are a number of different uses where you can just wear as a cell that is just sensitive to light from all directions it's actually useful so it must have started something like that so we now know why in window roughly when there are some animals that have just that still this is the larva of a sea urchin it has nondairy these non directional light receptors in several parts of its body to control circadian rhythms and control as a depth gauge as well mmm but we need kind of a tool okay we could use the like any interesting tool here if we ask the question what can receptor discriminate what can a light receptor tell apart what kind of tasks can it be useful if you want to use it for knowing that doing starts then you don't really need to discriminate very small intensity differences because the difference between a starry night and the sunlit day is eight orders of magnitude it's a huge difference so you don't need to be very precise but it turns out you need to could it collect photons and basically count photons even if our eyes do it or the photoreceptors do it in an analogue way they still count them and a small number means the large uncertainty so to be to be able to discriminate a certain level you need to collect a certain number of photons and then we can make a little mathematical tool where which tells us at what ambient intensity will the system work is there enough light for the system to discriminate what it should do and in order to tell night from day then it's easy small differences recall require a large number of photons of course but we calculate it and then it turns out that a system like this would work down to star light that's eight orders of magnitudes or eight log units below it will work there is enough photons around to tell something about the ambient intensity so we'll use this tool again with another outcome soon because it is important you can also ask can we get squeezed any more information out of this cell wouldn't it be nice to know where light comes from that would give us completely new ways of using it the only way to make this system sensitive to light only from some directions is to add some dark screening pigment that stops light from some directions but not from others and then we'll get another completely different function we'll get a directional light sensitivity which informs about the direction of like it can be used for phototaxis to guide animals toward darker places or towards brighter places it can also be used by the animals to control their body posture which might be useful to know what has happened down because like usually comes from above but there of course might be a little problem so let's apply our tool again to this system and ask at what intensities would this thing be able to cause now we're not interested in discriminating the huge differences between night and day were interested in discriminating bright a part of one scene - from a timid part of the same scene at the same time of day and the differences are now much smaller plus we have cut off half the light and another thing the changes over the day are slow so we can integrate over a long time now we can't integrate over such a long time anymore we have to make a short much shorter shutter speed or a higher shutter speed and all those things means that we need much more light so if we do the same calculation who turns out that this thing will work - about four orders of magnitude below bright sunlight below bright or at bright sunlight during the day on on on land if you're in water on let's just just about three meters of depth will of one order of magnitude so at six meters two orders of magnitude are gone at nine metres you've lost three if it's an overcast day you've lost an additional two which means that you easily eat up those four log units and then the system will not work anymore so if this system is actually not really very good because under very rare conditions will that sell with just obscene in its membrane be sensitive enough to do the discriminations you really need more sensitivity one of the problems is that it's only about 0.02 percent of the light that is absorbed I through passage by two passages through the membrane but it's of course easily solved just fold the membrane so light has to pass through many more layers of membrane so you make a stack of membrane instead you can make a much bigger stack than of illustrated here and then in sensitivity goes up and the thing starts to work again and you can now easily make it work down to seven orders of magnitude less than right daylight which is perfectly okay ten little work at dawn and dusk comfortably so now we've found something that is interesting stacked membranes and does that exist in like receptors yes it does yeah this is the case of all these animals we looked at before this is the larva of a rag worm it's got two directional light receptors like that that's a flat worm would to like to take this like that that's a jellyfish larva in all these cases there is a little pigment cell actually in that case it's the same cell that does everything there's a pigment cell and there is a sensory cell and the sensory cell has really massively folded membrane interestingly there are just two ways of incorporating opsins into stacked membrane so just two ways of stacking membrane or making lots of membranes in a small volume one way is to making micro villi you use actin filaments to push out the membrane the other way is to use cilia which use microtubules instead for the same purpose so modified cilia is one way of making lots of membrane microvilli is another you remember we said when we looked at the ops entry that I said that they were co-op since in our op since two different types of options it turns out that the there is a particular class of options that are associated with microvilli there is another type of up since the c options that are always associated with the modified cilia throughout the animal kingdom which means that these events or this innovation of folding membrane has probably happened twice really early in animal life it has happened twice and it has happened twice in the same common ancestor of all animals as well because actually all animals have these two types but they use them in different types of light sensitive organs there is another way to increase sensitivity and that is just to have more of these cells one since one cell has a particular sensitivity if you add more cells you have more sensitivity and if you have a number of cells you could sum their output in the nervous system but you could also compare it because these cells would actually shield each other a bit and if you make any little change like change the curvature like that these different cells will have very different views of the world they will look out in different directions and suddenly now we actually have the first eye this is the first vision everything we've talked about before is not really vision it's light sensitivity non directional light sensitivity or directional light sensitivity but this is vision even if you were only to have three different cells it would be an image of three pixels it is still vision and this is an example that of an animal that has something very similar to what we model there this is the eye of a flatworm it's a single pigmented cell in which you find a number of sensory cells light-sensitive cells with folded membrane other animals that have this which we can now call no resolution vision because it's not really a very sharp anymore and in these cases it's actually not sharp enough to see other animals they can see how their animals when the other animals are so close that you can basically smell them or touch them so it's not a long-range sense in that respect but they can see they're inanimate world they can see big structures in the world around them they can use it for to select their habitat that's basically what animals use it for that have that's just this lower resolution vision they will they can work out that it's a good good place it's over there in a bad place it's over they don't know where to go yeah and they can use sitter of course free even better body posture control and they can use it for movement control it'll tell them how much they move in relation to the environment when they turn they can navigate in straight lines and so on with this kind of vision so it's pretty useful but they cannot use it for seeing other animals they can't see predators they can't use it for seeing other animals to prey on them and they can't see each other the same species no actually I should go back here because yeah we've got to fly different animals that have this is that's a jellyfish and we've got the rag worm that we talked about before flat worms and here we have a starfish which have got a compound eye at the tip of its arm but wait a second we haven't talked about compound eyes how did that turning how did compound eyes evolve let's go back a bit to this number of receptor cells not with screening pigment next to one another if you turn it the other way around not fold it up like that but twist it the other way around you will get the same kind of information into it as when you got a pigment cup but now this is the start of a compound I instead yes so they're two actually equivalent solutions to the same problem that's another way of getting exactly the same information so now we've worked out why there are both single chamber dyes and compound eyes no difference in the beginning later on it turns out that single chamber dyes is actually a better solution compound eyes is not the world's most efficient way of using the space you've got to your disposal so let's go back to our a single cup I like this and we can ask the question how would you like how would you improve it to get better resolution well you actually have of course to squeeze more of these light sensitive cells into a larger cup then each of the cells would get a light from a narrower angle in space if you have a narrow angle angle in space it means that when you move things will happen faster so you would have to speed up your process of vision your integration time or your shutter speed would have to be faster the integrator of a shorter time which means you collect fewer photons for each of these moments and there is also a narrower angle so if we apply this tool that we tried before to calculate what kind of intensity and beam intensity you would need to make it work then it turns out that this only works down to a couple of orders of magnitude below sunlight so it's practically useless looks good but it will really never work if you if you have a very small number of cells like the flatworm it will work on sunny days but know this and actually you don't find in the eyes like that really in the animal kingdom that looks like that one way of solving it is actually to make to actually really exploit this membrane stacking to make the stacks really huge you have a problem here there's an open space there that that would probably very rarely happen it's a bad thing to have an open space like that it'll collect lots of crud in there that you have to look through or some other smaller organisms may find it as a place to live so you better put some cells in there to stop that from happening if you've got transparent cell in there you could just increase their protein concentration especially in the center and you would actually get a little lens the lens that converges light so you've got concentration of light from one point in space to a smaller area here and that would increase sensitivity see if you do these things you extend the stacks twos as long as you see almost absorb all of the light and you put a little dense it doesn't need to be perfectly focused on the retina or anything you increase your sensitivity anyway and the result is that that will actually work deep into dusk and dawn so it works again when you've made these improvements on it are there any animals now that have ice that look exactly like this that's the IR with box jellyfish comes very close to what we're modeled here yeah there are more examples a ragworm Asner that is almost identical to what we model here they're actually yet other ones these ones have eyes that come pretty close as well that type of eye what do you see with such an eye can you provide any useful information we can actually model that by using ray tracing technique so we work out computationally what each individual receptor cell will pick up from the environment and we can take normal images with a camera we can process the images and see this is what the velvet worm would see that's the result that's what we see that's taken with a fisheye lens so it has 180 degrees field of view that's the field of view total field of view of available worm with the velvet worm resolution now that looks useless if human had that kind of resolution you would probably call that person legally blind you wouldn't be able to drive a car be allowed to I guess velvet worms don't drive cars anyway yeah but it's pretty useful for them anyway because they what they need to need to know is where dark structures are so they can hide under them at dawn when they have been out hunting at night and the light of dawn starts they need to find shelter otherwise they would dry out and die well in in at in the evening they would have to work out what direction to get out of the sheltering into their hunting grounds so that's good enough for a velvet worm it's it's their purposes they can select their habitat and they can be in the right place but they don't see each other until they actually touch them this is a box jellyfish it's got c1 leelai' up there they've got four of these little clusters each cluster looks like that's got a couple of eyes what do they see now that's what a box jellyfish would see if they went on a roller coaster right now you've always all of you have thought about that for all your life what does the box jellyfish actually see when they go on they're all okay so right now you get the answer and it's not all that much it's good enough though for box jellyfish this particularly the species here it lives in mangrove swamps it needs to steer around mangrove roots because there are lots of nasty organisms on the route so they don't want to collide with roots they never get stranded because they can see when when it's too shallow they never drift out into the mangrove Lagoon because they want to stay under the mangrove canopy that's where there is lots of food they don't see their food but they actually see the mangrove canopy so they can that that resolution is good enough to steer away from mangrove roots and to bring them back in under the canopy it keeps them in the right habitat but they don't see each other they don't see the food yeah no that may not be the really the most natural habitat of a box jellyfish it's kind of fun I'm not sure the box jellyfish would find it that sort of amusing I'm not sure they would even realize what would what's going on that's another matter maybe they would get motion sick so if we want to know we've talked about low resolution vision there are lots of animals that have a lower resolution vision they can't and the definition of it is that they don't the resolution is not good enough to see other animals so they can see the inanimate world and they can use that to navigate and move within the inanimate world all these eyes are small they are really less than a millimeter so if we want to improve on this system we have to make something larger and that is what has happened the animal groups that have higher resolution vision good enough to actually see other animals they have much larger ice much bigger than a millimeter and then you can actually see things then you get enough light as forbearing where in there as well and it's really the lens that makes it sensitive enough because you need to concentrate light rather than having the light that reaches a naked light-sensitive cell which may be five microns across you can have light that reach the lens that is five ten millimeters across which is a much is a huge area compared to the single cell so the sensitivity is way bigger and actually and animals with these types of eyes can see at any kind of place on earth you can even see in the deep sea at really low intensity is much lower than we can see we'll come to that very soon animals that have higher a solution vision it's not actually all that common among animals it's only a small number of animal groups that have it vertebrates is certainly one we find it in insects we find it in some spiders and we find it in cephalopods in octopus squid and cuttlefish those other groups and there are as few little exceptions and among other crustaceans and a few little exceptions among some other mollusks and some rag worms that isolated cases that have just made it across the border to to higher resolution vision but it's mainly these large groups that have there is an interesting difference then between the vertebrate eye whether it's kwatak all terrestrial and octopus and squid eyes they may look identical in octopus and squid I may look identical to a fish eye if you look at them at low resolution but if you look at the details you will find that vertebrates have ciliary based rods and cones we would see up since in them that are turned upside down so they actually point away from the light that's the silly solution we have where we actually need a blind spot to get all the the accents out of the retina that's X inside of the eyeball and in the cephalopods it's much more wisely designed because they're the light receptors actually facing the light they use micro villi and not modified cilia and they have the other type of opsin re-pour oxen so that's clearly evolved in parallel completely independently reached very very similar in results and as I said this solution can be used for really low intensities as well it's just a matter of making the eye really large some animals have made the eye really large and those are particularly deep-sea squid yeah there is a colossal squid here they're actually part of it the is over there that's the eyeball and that's the opening where you can see a part of the iris there actually it's it's frozen and it's just throwing up my hand is over there that's a scale bar that eye is 27 centimeters across it's a pretty sizable eye relative to that colossal squid is the giant squid over here which is also got an eye are the same size 27 centimeters the scale bar lair is in American fuel house which runs right over there pupil so we could know exactly how large the eyes and these eyes are useful at a thousand meters depth they can actually see sperm whales hunting for them at that depth the sperm whale can't even though it's got pretty big eyes can't see a thing sperm whales use sonar instead to detect the squiggly so when did this high-resolution vision appear if we go back to Cambrian fossils it seems in the early cambrian there were plenty of animals that had higher resolution vision most of them actually had compound eyes in those days but there were also representatives with single chamber dice like ours it's a high resolution vision which allowed visually guided predation it was really cold for good eyes to see predators and escape from them and animals that interacted with vision between within the species to see find mates to determine if the mate is what kind of sex it is to communicate visually all those things seems to have been around about 540 million years ago but just a little bit earlier in the the Acheron there were nothing like that the high-resolution vision seems to have evolved pretty suddenly or pretty quickly at least at the onset of the can bring so now we've timed that event as well we know roughly when it must have happened and we can now look at the timing we know that that's the border between the Cambrian and the Ediacaran so around that red line 540 million years ago plus minus a couple of ten million years or so high resolution vision must have evolved from lower resolution vision yeah we can also say that the complete other things events from just the first light sensitivity with opsins to lower a solution vision being pretty good that must have happened in this almost 200 years which may actually have been almost 300 million years if it started around eight hundred million years instead so most of the I evolution would have been completed in that time many years ago I made a calculation of how long how many generations it would take for an eye to evolve just to make the with low selection or with weak selection just to make the more vacations in shape it turns out that can be done in 350 generations if one generation is one year then that's 350 thousand years that's not really a very long time on these geological scales so ice could have evolved many times yeah in in this period here it's not a hard thing to do but then again it's not actually ice themselves that had to evolve just an eye on its own is a rather useless thing unless you have a brain behind it or a nervous system that can generate behaviors and what has actually been driving evolution all the way is not ice themselves but it's the visually guided behaviors so visually guided behaviors must kind of be there first and puts some pressure on on better performance of the visual organs and then selection will actually act on the visual organs but primarily it works on the visually guided behaviors so vision is really a matter of the evolution of visually guided behaviors and I think we've now worked out what the different tasks than different types of behaviors or in which sequence they actually evolved it must have started with non directional light sensitivity which turned into directional light sensitivity still not vision which turned into low resolution vision when I roughly when that happens but not very precisely we know more when that happened we know quite precisely when high resolution vision evolved low resolution vision that was it at the onset of the camera but now of course there are things that complicate matters there always are so it doesn't always go that this three straight simple sequence also something that's actually happened after the Cambrian till now it's not what's not that everything stopped number of new cases of eyes have actually evolved these are some of them the ice we find in scallops and in our clams these are not ice on the head these are eyes on another part these eye animals have been modified after the Cambrian explosion into other body shapes new eyes have evolved in new places and in this case it seems that he must because all clamps have light receptors which are used as shadow receptors on the mantle edge and a small group of of clamps and scallops scallops being one of the groups have actually evolved eyes and that seems and they used it for predator detection so they are basically burglar alarms they don't use it to see each other they don't use it to to hunt for anything but they are still if we use the classification that high resolution vision is when you can actually see other animals that is high resolution vision but it is developed may be developed straight from light sensitivity so bypassing the low resolution or directional light sensitivity low resolution vision we have an equivalent case in fan worms two different groups of fan worms the sibelius and the SAP you-let's seems to have done it in different ways these Sibel eats they have a one pair of these feeding tentacles that are modified with a little compound eye on top if you look into the photoreceptors they they look like nothing they've reinvented the wheel it is not they haven't borrowed a photoreceptor there was some somewhere else they really reinvented everything they still use obscene though same thing here they've turned or generated a boomerang shaped eye which is good enough as a burglar alarm it'll tell them when a fish is approaching and about to take a bite of their tentacle crown and then they'll see that before the fish can react the whole worm is pulled back in it's not visible anymore to the fish so it serves them serves a good purpose for them now we can actually start to work ask the question how many times have these different transitions happened and we now know quite roughly at least how many times it has happened the melatonin receptor has probably evolved only once from that it seems opsins have evolved only once from these non directional photoreceptors in two directional photoreceptors it has happened at least thirteen times possibly twice as many times it's hard to say but at least that number from directional photoreceptors to lower resolution vision so that's the origin of real vision has happened at least 15 times sometimes it turned into single chamber dye sometimes it turned into compound eyes so the compound we have the compound eyes on the various worms and compound eyes on on starfish arms and we have the compound eyes of arthropods there flatworms actually also have compound eye some of them and then from low resolution vision to high resolution vision that has happened about nine times possibly more so we know how many times this all these things have happened we know why it has happened we know roughly how it has happened and when it has happened so I think we now can answer all the questions we set out to answer why when and how why when and how yes that's exactly the questions I think we've answered thank you [Applause] so I mean thank you that was just amazing I mean I knew that there were was a great variation in AI structures you know across so many animal kingdoms but I really hadn't appreciated how deeply rooted the similarities and many of the differences were that's just extraordinary so I mean okay just thank you so much for coming and making all the things so simple and really in reality it's obviously so complex next week we're moving away from biology next week's lectures can be the fourth in this series is the vision of future technology so miss Sophy Hackford who is a futurist and co-founder of the data and AI artificial intelligence company 1751 labs it's going to come and talk about new technologies and how interconnectedness means that our world is becoming entangled with machines that's like scary stuff to me but I hope we'll see you them but damn thank you so much for coming to Cambridge to talk to us tonight it was a delight to have you into [Applause] you

Channel: Darwin College Lecture Series

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Keywords: Darwin College Lecture Series, Evelution, Eyes, Vision – 2019, Dan-E. Nilsson

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Length: 48min 19sec (2899 seconds)

Published: Thu Feb 07 2019