Iversen wrote:Yesterday I watched a TV program about people with weird faculties, and the phenomenon of tetrachromatics was named. It refers to an extremely small number of women who have four kinds of colour receptors (tap cells) in their eyes, which would allow them to see many more color nuances than ordinary people. Why only women? Well, the clue is that they have male relatives with color viewing deficiencies. This is caused by a mutatation in their one and only X chromosome. However a woman with two X chromosome may have one deficient X chromosome and another which is normal - and then she has four different kinds of taps. There is a test on the internet which claims to test for this condition, but it is a total fraud. You need some specialized screens to show the relevant test. Forget about it. I did however take another test called the Farnsworth Munsell 100 Hue Test, and you can take it for free at a site called Colormunki. You move small squares around so that they form four continuous rows of hues. I got 0 errors, which isn't unheard of, but a reassurance that the colors on my paintings aren't caused by faulty color perception. But some paintings are. The great Monet got his eye lenses removed late in late due to cataract, and the glass lenses he got instead didn't shut out the ultra violet light. The funny thing is that we should in principle be able to see ultraviolet, but our eye lenses block that colour. So when Monet had his operation he must have experienced a change in his color perception, and some art historians have claimed that they can see the difference in the choice of color on his last paintings. Well...
Today I have been watching the equally great Attenborough tell about paleontological marvels. He started out with the Ediacaran fauna from around 635.000.000–542.000.000 BC(which I have mentioned several times before). Please allow me to digress: In the otherwise reasonable trustworthy QI quiz on BBC this period was mentioned, and then poor gullible Sandy Toksvig quoted the crap information from her elves that the first great extinction on the Earth happened when sea anemonae popped up and ate the whole bunch (illustrated by the flat and blind and defenseless Dickinsonia to the left below). Bahh...
Actually there would almost certainly have been been an extinction already due to the preceding Snowball Earth episode (and, yes I have also written about that - after reading about it in a long article in Russian), but the soft critters that may have predeced that event are hard to trace in the fossil record. However the main point is that the sea anemonae almost certainly didn't eat the rest of the Ediacarans. But there was at least one ghastly predator around, the Anomalocharis, and the supposition is that the appearance of predators forced the prey animals to acquire armour and better senses. And that's where we enter the next phase with the trilobites at the onset of the Cambrian ... and they had not only armoured tripartite shields, but the most amazing variation of silicate eyes you could imagine. Everything alive since then has made eyes of soft tissue (even insects and spiders), but not the trilobites. You can find a whole article about trilobite eyes here, including photo nr. 4 below. I took a photo (no. 3) from the TV screen of one trilobite found in Morocco and supposedly at view in a museum in a Moroccan town called Erfut (?) - I have to go there sometime! - but unfortunately this animal is more in the funny spikes department, not so much in the clever eyes section.
There is only one snag with all of the above, namely that the information was given in English, so I haven't really studied other languages since yesterday. But on the notestand beside my soft chair I have an article about chocolate in Albanian and another about the chaotic period after the death of Sigurd Jorsalafar in Old Norse, so later today I'll make amends for my temporarily restricted linguistic horizon.
The Ediacaran is fascinating! I wish there was more media out there about it. What's more, there are some hints that multicellular life had existed more than one billion years before the Ediacaran - shortly after the Oxygen catastrophe. Speaking of which, it (the oxygen catastrophe) was the first great extinction event, so the total major extinction are in fact 7, not six.
But yes, one of the hypotheses why Ediacaran biota went extinct was that it was immobile and defenceless to the newly emerged mobile predators.
Tetrachromatic vision is also interesting. We are one of the few mammals that can see in three colors, several New World monkeys being the others (I think, there might be a few more also). All other mammals see in just two colors, so seeing in four colors puts you in the, dunno, the 0.00001th percentile? Regarding mammals anyway, since all birds and lizards see in four colors. Given that birds of paradise are already so colorful, imagine how they see themselves with the extra base color they perceive!