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

Mammalia

n Color Visio

n

Color Vision Almost Reason Enough for Having EyesJay Neitz, Joseph Carroll and Maureen NeitzOptics & 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 NathansScientific American April 2009 page 60

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

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

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

Organization of the Human Trichromatic Cone Mosaic. Heidi Hofer, The Journal of Neuroscience, 2005 • 25(42):9669 –9679

The Evolution of Primate Color Vision by Gerald H. Jacobs and Jeremy NathansScientific American April 2009 page 63

Gene therapy in colour Robert ShapleyReplacing a missing gene in adult colour-blind monkeys restores normal colour vision. How the new photoreceptor cells produced by this therapy lead to colour vision is a fascinating question.

• 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