The Earth was once not nearly as colorful as it is today. Monochromatic forests dominated the landscape WAY before the first colorful flower did, and this forever changed the way animals actually see! Color seems like such a minuscule factor in the evolution of animals, but Shubin believes it was the primary factor that led to the formation of the modern-day human eye. On page 151, Shubin displays four different eye structures that allow an animal to see objects at different levels of clarity. In order to understand how and why eyes have evolved the way they have, we must "understand the relationship between the structures that make our camera-eye and those that make other kinds of eyes". Primitive eyes contain molecules that allows the animal the see in black and white, which displays a very blurred image. But modern eyes contain molecules that can see colors, which create images that are crystal-clear. How could color be a primary reason why eyes have evolved the way they do? How does this relate to the Relationship between Structure and Function? (pg. 154 gives a hint)
Mikey Ling
(mikeyling@ymail.com)
As the forest became more colorful, it became important for humans to be able to identify potentially dangerous things. The eyes function to work with the brain when it comes to associative learning. Without colors, it is much harder to associate an object (or a similar object in that case) to an experience one has had. This would cause many organisms to repeatedly make the mistakes over and over again. This is important when it comes to both food and predators as very often, colors are the main key when it comes to danger.
ReplyDeleteOne of the downfalls to other animals beginning to see color as well is that prey have devised tricks to fool other color seeing animals. One way is through mimicry (both Batesian and Mullerian) as the animals take advantage of this associative learning to resemble another organism that is not prey.
Considering that the function of the eye is to be able to signal the brain of anything in the environment that could affect the organism in either a negative or positive way. This means that it is important for the eye to pick up any details that could be important and be as clear as possible. This will allow for the organism to see danger long before it becomes too large of a threat. For these reasons, evolution caused eyes for humans to see in color because the ones that had this advanced sense was more likely to survive, therefore making it an advantage. Colored vision developed when, “ancestors of modern monkeys, apes, and humans switched to diurnal (daytime) activity and began consuming fruits and leaves from flowering plants” (http://en.wikipedia.org/wiki/Color_vision#Evolution). It gave clues to whether the food is ripe, spoiled, or poisonous. If humans were nocturnal, then this adaptation would have never been produced as then colors would not be very visible and therefore unhelpful.
Jackie James
(jackie.james@comcast.net)
Like Jackie mentioned, the switch to color vision most likely correlates with the switch from a “monochromatic forest to one with a richer palette of colors in food” (154). By developing color vision, animals can use their “associative learning” (Jackie) to distinguish between a good meal and a bad (i.e. poisonous) meal: “it [gives] clues to whether the food is ripe, spoiled, or poisonous” (Jackie).
ReplyDeleteIn addition, Jackie mentioned that there are some “downfalls” (Jackie) associated with color vision such as mimicry to fool an animal into not eating the plant or animal because they look like another animal (i.e. they do not look like what the predator would prey on). However, I would not look at this as a “downfall” by any means. Instead, the development of color vision gave way to adaptations and co-evolution in a different “light” (pun intended), allowing plants and animals to survive and reproduce in different ways.
First, relating back to the ecology unit like Jackie mentioned, there were four defensive adaptations to predation we read in Campbell over the summer: cryptic coloration, aposematic coloration, Batesian mimicry, and Mullerian mimicry. As terrestrial life became richer in different colors, some animals developed adaptations to camouflage themselves to make it difficult for predators to spot them (cryptic coloration), developed warning signs to scare of predators (aposematic coloration), developed the ability to look like harmful species (Batesian mimicry), and the ability to have similar colors as other unpalatable species (Mullerian mimicry) (Campbell 1201).
In addition, in the angiosperm unit, we learned about the co-evolution of flowers and their pollinators. As the lens of animal’s eyes became more acute, the colors and shapes of the flowers became more important as colors and shapes of flowers offer “some kind of attractant to advertise the presence” of some kind of an award the animal will get from pollinating the plant such as food and nectar (http://biology.clc.uc.edu/courses/bio303/coevolution.htm). The colors of the flowers are also dependent upon the colors their pollinators can see (http://biology.clc.uc.edu/courses/bio303/coevolution.htm). For example, some bees do not see red, but they can see yellows and blues. Thus, the flowers that use these types of bees to pollinate usually have yellow or blue colors. Another example is flowers that use butterflies as their pollinators. Many butterflies can see red, but their sense of smell is weak. What is really fascinating is that many flowers that butterflies pollinate will be brightly colored, but odorless (http://biology.clc.uc.edu/courses/bio303/coevolution.htm)!
Relating to the structure and function part of your question, invertebrates and vertebrates have different ways to increase the light-gathering surface area in the eye tissue to see more vivid images. In invertebrates, they have numerous folds in their eye tissue to enhance vision. In vertebrates, their “lineage expands the surface area by having lots of little projections extending from the tissue like bristles” (154).
(Bobby Muttilainen, rmuttilainen@gmail.com)