Students Returning To School After Labor Day -- September 5, 2020

Students will be returning to high school after Labor Day here in north Texas. Look at the efforts put into health and safety: link here.

What caught my eye: every time a student takes a "new" seat, he/she will capture a QR code on their mobile device which will be used for contact tracing if needed. We have truly entered a new world. It can also be used for attendance. It could also be used to track "cheating" on tests, I assume. 

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Evolution

I'm still in my "evolution" phase. 

Of all the big land animals of which most humans are familiar, the turtles remain the most enigmatic with regard to their evolutionary history and where to pigeon-hole them in those evolutionary wiring diagrams. 

The key certainly rests with their vision. Curious, googling brought me to this article in Science News from a couple of year ago: The "red gene" birds, turtles, suggests dinosaurs had bird-like vision.

I never had any doubt about that. I was more curious about how that "red gene" might help sort out the evolutionary relationship between birds, turtles, and dinosaurs. 

Some data points from the linked article:

• a gene for red color originated in the reptile lineage about 250 mya; this was just a few years (geologically speaking) after the greatest extinction event in history, the Permian Mass Extinction (252 mya); assuming the authors of the linked article were "precise" in their use of words, the red gene originated after that extinction
• that red vision gene expressed itself in those animals that had it by being able to see bright red bird feathers and "painted" turtles;
• because both are related to dinosaurs, the authors surmise the dinosaurs may have also had that "red vision" gene
• that "red vision gene" was first discovered in early 2016 by scientists studying the zebra finch;
• in 2016, it was also reported that the same gene shows up in turtles;
• the gene: CYP2J19
• but look at this: the gene allows birds and turtles to convert the yellow pigments in their diets into red pigments which then end up as retinal oil droplets; the droplets heighten color vision in the red spectrum;
• among existing tetrapods, only birds and turtles have these red  retinal oil droplets;
• unlike mammals, avian and turtle retinal cones (color receptors) contain a range of brightly-colored oil droplets, including green, yellow and red;
• these oil droplets function in a similar way as filters on a camera lens;
• the droplets give birds and turtles much better color vision than mammals:
• humans can distinguish between some shades of red such as scarlet and crimson; birds and turtles can see a host of intermediate reds between these two shades;
• in some birds and a few turtle species, that red pigment is also used for external display: red beaks and feathers or the red neck patches and rims of shells in species such as the painted turtle;
• scientists traced the history of that red vision gene
• the "red gene" originated around 250 mya;
• predated the split of the lineage from the archosaur line, and,
• runs right through turtle and bird evolution
• if so, it means that dinosaurs would have also had the "red gene" unless of course they "lost it" for some region -- because dinosaurs (and crocodiles) split from this lineage after turtles;
• crocodiles: they appear to have lost the CYP2J19 gene and have no oil droplets of any color in their retinal cones;
• scaly lizards and snakes split from the archosaur line before the turtles and these reptiles lack retinal oil droplets, or have yellow and green but not red (interestingly enough, scaly lizards and snakes do have external red coloration);
• there is some evidence that oil droplets were lost from the retinas of species that were nocturnal for long periods of their genetic past, and that this hypothesis fits for mammals and snakes, and possibly crocodiles
• but there's more and this would get Richard Dawkins excited;
• it is surmised that the "external redness was often sexually selected";
• Dawkins maintains that the greatest driver of evolution was sexual selection;
• evolution moves most quickly when there is a sexually-predisposed reason;
• that would help explain the huge diversity of dinosaur species
  

See also this post by another blogger. Well done.