Box 6.3 Evolutionary Psychology

Fig 6.17 Bowerbird Nests

Animals exhibit different degrees of color vision. Four categories of color vision capabilities among mammals: Minimal color vision with only a single kind of cone pigment and must rely on interactions between rods and cones to discriminate wavelength found in raccoons Feeble dichromatic color vision with two kinds of cone pigments but very few cones found in cats Robust dichromatic color vision with two kinds of cones and lots of cones found in dogs Excellent trichromatic color vision Certain primates such as humans and old world monkeys have good trichromatic color vision based on three classes of cone photopigments However, unlike mammals most birds and reptiles have tetrachromatic color vision

Mammalian Color VisionMammalian Color Vision

Color Vision Almost Reason Enough for Having Eyes Jay Neitz, Joseph Carroll and Maureen Neitz Optics & Photonics News, January 2001, page 28

Transduction

Evolution of vertebrate visual pigments. James K. Bowmaker, Vision Research 48 (2008) 2022–2041-0

Humans and Old World monkeys have three different cone classes short (S) wavelength sensitive cells with maxima near 415–430 nm middle (M) with maxima at 530–537 nm long (L) with maxima at 555–565 nm New World primates have variable cone phenotypes spider monkey are trichromats Cebus and squirrel monkeys, the males and some females are dichromats, while other females are trichromats owl monkey are monochromats New World monkeys have only one cone pigment gene per X- chromosome trichromatic variation in females is based on the presence of allelic diversity at the X-chromosome opsin gene locus only heterozygous females have two genes that encode two different middle-to-long wavelength photopigments Primate Cone Variation

The Evolution of Primate Color Vision by Gerald H. Jacobs and Jeremy Nathans Scientific American April 2009 page 60

The Evolution of Primate Color Vision by Gerald H. Jacobs and Jeremy Nathans Scientific American April 2009 page 61

The Evolution of Primate Color Vision by Gerald H. Jacobs and Jeremy Nathans Scientific American April 2009 page 62

The Evolution of Primate Color Vision by Gerald H. Jacobs and Jeremy Nathans Scientific American April 2009 page 62

Having three cones types does not produce trichromatic vision Cones need to be connected in an opponent system +L/-M -L/+M This requires special circuits from Cones to Bipolar to Ganglion cells Primates have an additional class of “midget” retinal ganglion cell receives its input from a single cone cell midget ganglion cells encode fine spatial detail first evolved to connect single cones to the brain enabled the detection of separate M and L opsins when they appeared in primates Midget ganglion cells are not present in other mammals. Color Vision Requires Opponent Processing

Color Vision Deficiency “Color Blindness” Most so-called color-blind humans (actually color-deficient humans) have dichromatic vision and can distinguish short- wavelength stimuli (blue) from long-wavelength stimuli (not blue). Introduction of photopigment genes into animals with dichromatic vision suggests we may be able to correct dichromatic vision in humans. Most color-blindness in humans is due to the absence of cones sensitive to medium-wavelength light (M cones). Because women have two X chromosomes, a defective gene encoding for the medium-wavelength pigment on the X chromosome is almost always compensated for by a normal copy of the gene on the other X. This is why men are much more likely to be dichromats than women are.

Simulating color blindness Deuteranopia: missing M-cone, 1.5% males

There is a number in the center of the circle. If you can see the number, chances are you are not color- blind. Plate 1 Those with normal color vision should read the number 74. Plate 2 Those with normal color vision should read the number 6. Charts used to test for color-blindness

Color Vision Deficiency Monochromatism: Either no cones available or just one type of them, Rare Dichromatism: Only two different cone types, the third one is missing completely –Tritanopia: missing S-cone, rare –Deuteranopia: missing M-cone, 1.5% males –Protanopia : missing L-cone, 1% males Anomalous trichromatism: All three types but with shifted peaks of sensitivity for one of them. This results in a smaller color spectrum. –Tritanomaly: malfunctioning S-cone, rare –Deuteranomaly: malfunctioning M-cone, 4.5% males –Protanomaly: malfunctioning L-cone, 1% males

Color Vision Deficiency Deuteranope Tritanope normal color vision Protanope Anomalous trichromacy

Red-green color blindness Archaic terminology, should be “color vision deficiency” Red-green color blindness is a generic term for: –protanopia (red-blindness) missing L-cone –protanomaly (red-weakness) malfunctioning L-cone –deuteranopia (green-blindness) missing M-cone –deuteranomaly (green-weakness) malfunctioning M-cone More than 99% of all color blind people are suffering from a red- green color vision deficiency –About 8% of all men and 0.5% of all women are suffering from it. –Varies in severity –Recessive, sex linked trait on the X chromosome –This results in many more men than women. –It is usually inherited from a grandfather to his grandson, with the mother in between acting as the carrier of the disease Not just red and green, but the whole color spectrum is affected by color blindness.