November 01, 2004

Researchers provide concrete evidence about how the human eye evolved. [Via /.]
  • Love this stuff. Thanks homunculus.
  • If only you could have seen what I have seen with your eyes.
  • ..and that is one of the best user names i've seen so far. 'specially in a science geek FPP comment thread. (even if all you are is a sock puppet...)
  • cute
  • Sock? /head explodes
  • If only you could have seen what I have seen with your eyes. I've been thinking about that scene a lot since I read this.
  • Cool science. The Darwin angle puzzles me. Is there a single intelligent, educated person on this planet who still thinks that there are grounds for debate here? Evolution is an observed, tested fact. We don't understand all the details. Far from it. There are huge, wonderful, challenging vistas of the natural world opening before us in biology. Every answered question raises many more fascinating questions. But evolution happens. We've seen it happening. There is no biological phenomenon that it can't explain (often in many ways). Everybody who has studied it at all knows this. Why should anyone care about the few remaining morons who won't accept it? There are about ten lifetime's worth of work I want to do in understanding the mechanisms of life. Maybe ten lifetimes is only enough to write the contents page for what I would like to study. Much of what we think we know is wrong. Much more is inaccurate or incomplete. But the basic ideas of evolution have not been successfully challenged in almost 150 years. It's predictions have been observed. I don't know of any other theory with that pedigree. Can't we just get on with the huge amount of really cool science now?
  • But it's just a theory, like Creationism is a theory! :P
  • Why should anyone care about the few remaining morons who won't accept it? Because unfortunately some of them have express governmental permission to pass their faith-based mindset onto the next generation, giving that information a chance to propagate and lead more people in the wrong direction. /staunch evolutionist
  • tracicle: You're absolutely right. But why should you have to call yourself a 'staunch evolutionist' any more than you call yourself a 'staunch gravitationalist'? dj: I know you don't need telling, but just in case a twit who doesn't understand should drop by: Hypothesis: A model that makes testable, falsifiable predictions.
    Theory: A hypothesis which has undergone repeatable, repeated tests without being falsified.
    Faith: Anything which you believe whether or not it's unprovable, farcical or just plain wrong.
    Lie:Something that has been proposed, tested, shown in a repeatable way to be wrong, and you then recount as fact. Evolution is a theory. Creationism is a lie.
  • Not going to get into another evolution v. creationism debate here, but I'd like to point out the article is completely uninformative. "It is not surprising that cells of human eyes come from the brain. Great. Where does the brain come from? Where do cells get off mutating into light-sensitive brain cells, from which eyes could potentially originate? We still have light-sensitive cells in our brains today which detect light and influence our daily rhythms of activity," explains Wittbrodt. "Quite possibly, the human eye has originated from light-sensitive cells in the brain. This sounds like wankerism to me. Light-sensitive brain cells still need to be exposed to light or have light information sent to them, implying an opening in the head. In other words, the eyes. How else do light-sensitive cells in the brain respond to light?
  • f8xmulder, I believe they are referring to the Pineal Gland. It's called the third eye due to it's light sensitive properties, and it "influence[s] our daily rhythyms of activity" by producing melatonin. I agree with you that this article pretty uninfromative. It doesn't answer the question, just kinda dodges it. The scientists discovered that two types of lightsensitive cells existed in our early animal ancestors: rhabdomeric and ciliary. In most animals, rhabdomeric cells became part of the eyes, and ciliary cells remained embedded in the brain. But the evolution of the human eye is peculiar ­ it is the ciliary cells that were recruited for vision which eventually gave rise to the rods and cones of the retina. So what about primates? Do they have ciliary vision or rhabdomeric? I think it'd be very interesting to find out what animals do have ciliary vision, and how closely are they related.
  • Yeah, I got a strange feeling of stuff being glossed over from this too. I'm not saying that there might not be some interesting work at the root of this, but it didn't exactly grab me. For a start, it overstates the extent to which eyes are an evolutionary mystery. They're not really, and they haven't been for quite a while. Hmmm. Maybe my main criticism of it that it doesn't immediately seem to be about Hobbits. I think Homo floresiensis has been spoiling us terribly of late - if it's not as exciting as that, then I'm not interested...
  • Mr. Knickerbocker, thank you for the info. I had no idea. However, from the Pineal Gland link: Light can be detected by the suprachiasmatic nucleus (SCN) which has directs connections to the retina So again, this doesn't seem to support the conclusions raised by the article, which is, no doubt, merely a gloss and nothing more. Still, I am somewhat miffed that it's assumed that people will just accept this stuff carte blanche.
  • Because the cellular changes that took place, f8x, changing brain-type cells into light-sensitive cells, happened a very, very long time ago, in fish, or fish-like creatures. Studies of the eyes of cartilaginous beasties like cuttlefish & so forth demonstrate the process today; the variations of complexity in light-sensing cells from primitive to sophisticated are still observable in various species today.
  • Besides which, a photochemical response is just not that improbable. Certain brain cells could be responsive to light just as a consequence of them doing what they're "supposed" to be doing. Alternatively, all brains (and hell, not all creatures have brains as such so nerve tissue) are not completely encased in thick enough bone to shield the tissue from light. That some brain cells are light responsive is not some huge mystery that itself needs solving.
  • Why are there photosensitive areas behind the knees?
  • f8x, it's a press release. If you want to complain about lack of details, request a complete copy of their finding and read that first. The contect details for doing so are at the bottom of the release. For now, settle down.
  • The Dangers of the Pineal Gland!!! ;E And I think if the "theory" of Gravity is going to be taught in our schools, we should also teach the theory of Underground Bone Magnets and Planetary Sucking. You know, in the interest of a well-rounded education Damn liberals.
  • the SCN is directly connected to the retina via the retinohypothalamic tract. the SCN has no direct connection with the pineal, and has no light-sensitive cells, nor does it contain opsins or other light-detecting proteins or peptides. the pineal in mammals is not involved in circadian rhythms, not directly anyway (secretes melatonin but does not oscillate on its own.) it's also burined beneath an inch or so of brain and skull, through which no light can pass. in birds, the pineal isn't buried beneath so much brain and skull, and it does detect light, and it does drive rhythms (transplanting a chicken pineal to a pinealectomized chicken will restore locomotor rhythms). but in both bird and mammal, the pineal has light-sensitive cells - they just don't function as photoreceptors in mammals because they don't see light, and haven't seen light (on an evolutionary scale) for millions of years. the eyes grow as outpockets of brain tissue, much like the anterior pituitary does. so although where the tissue that becomes eyes originates, on a germ-layer basis, is well known (it's ectoderm: neural plate ectoderm becomes neural tube, part of which becomes retina, and skin ectoderm over the developing optic bulbs forms lens and cornea), we didn't know why this tissue was light-sensitive to begin with, and that was the missing bit in the eye evolution theory. it's been shown before that even a partial eye (given a photodetecotr) is useful, yet the evolutionary origin of the photodetector wasn't clear. it needed to be hooked to the brain, and we know it originates from brain tissue, but why we would have a bit of photoreceptive tissue in our brains to begin with... well, the worm anatomy helps. it shows us where these ciliary cells that ended up in the retina came from, and as for the other ciliary cells in the pineal, well, they just stayed where they were. (oh and all vertebrates have rods and cones. it's part of our evolutionary history - not just in primates.) /circadian biologist who teaches developmental biology and comparative anatomy
  • I think you'll find that the SCN is directly connected to the retina, via the retinohypothalamic- Oh. On preview: what caution live frogs said. ;-)