Download Reflection 2 Eyes

Nick Gardner
Campbell
Anthropology 1020
07/18/14
REFLECTION 2: THE EVOLUTION OF THE EYE
Evolution is history’s greatest inventor. So marvelous are the creations it has managed to
produce, that even with our advanced technology, we humans have yet to match many of them
completely. Among these ‘inventions’ is one that is perhaps its greatest of all, and one that has
done more to fuel the evolutionary process than anything short of DNA: the eye. This opus is
often taken for granted by most – it is after all one of the most omnipresent features in nature:
nearly every conceivable creature possesses it in some shape or form. Ranging from the
exceeding simple (“eye spots” that can detect only light) to the staggeringly complex (the
compound eye of a dragonfly), the eye is undoubtedly one of the masterpieces of nature.
And yet, because of the sheer amount of intricacies that go into making the eye function just
right, many have scoffed at the notion that natural selection could feasibly produce an organ of
such complexity. Doubters looked at the eye and knew for certain that this, if anything, was
proof of an intelligent creator working behind the scenes. Even Darwin was baffled by the eye,
going as far to write in The Origin of Species that the idea of natural selection producing an eye
“seems, I freely confess, absurd in the highest possible degree”. (Carl Zimmer, How the Eye
Evolved, New York Academy of Sciences Magazine, 2009)
Curious as to how such an organ could have evolved, I decided to dedicate my next reflection to
answering the question. My primary source was a short documentary film appropriately titled
Evolution: How Eyes Evolved. The documentary happily started right at the very beginning,
detailing just how and when the first eyes developed.
It began nearly 600 million years ago during the Cambrian explosion, a period of rapid
appearances and developments of most major animal phyla. During this time an evolutionary
arms race was taking place, and two different types of eyes manifested as a result: simple light
detecting eye spots, and compound eyes. Eye spots, as mentioned, were simple constructs,
typically made up of a few cells, which could only detect wavelengths of light. Compound eyes,
as the name might suggest, were significantly more complicated; multi-lensed, and with the
ability to discern shapes and movement, these eyes were developed as both a response to and
facilitator of predation. The earliest species known to develop these are the trilobites.
Indeed, their role in predation is perhaps the key to their importance in evolution. Instrumental in
both finding prey and avoiding predators, natural selection – and by extension, evolution – would
likely be completely different had the eye not ever developed.
The film goes on to discuss the multitude of creatures that have since used the compound eye:
with insects being the most prominent users (making the compound eye the most common type
of eye in the world). Though the focusing power of compound eyes is poor, their processing
power far outstrips that of human’s.
The next half of the documentary concerns itself with the type of eye we humans are most
familiar with: the vertebrate eye. Evolved from the aforementioned eye spots, the vertebrate eye
is significantly different from the compound. Single-lensed and present in everything from birds,
to reptiles, to mammals, the vertebrate eye’s strength varies enormously among species.
Binocular vision, night vision, 360 degree vision, and color vision – all variances of the
vertebrate eye – are each discussed at length. Most compelling is the discussion of primate’s
eyes. As we’ve touched upon in class, primates possess some of the most advanced eyes in the
animal kingdom. Their eyes are binocular; a rarity among non-predators, but a necessity for
primate life. The increased depth perception imparted by the binocular eye is especially useful
for life in the trees, as measuring distances between branches is made much easier. Primates also
possess some of the best color vision in the animal kingdom – with humans themselves being
able “to decipher 2.3 million colors with the color and precision that puts computers to shame”.
(Evolution: How the Eyes Evolved, Kurt Tondorf, Stephanie Angelides, Shelley Schulze, Larry
Engel, 2008) This in turn is no less important than binocular vision, and some scientists have
hypothesized that this advanced color vision developed as a method for distinguishing ideal
foods.
The documentary ends with an interesting hypothesis: that vision and eyes may have fueled the
development of intelligence in primates. In other words, the development of the primate’s eye
may have played an integral part in the road to becoming human. Because the primates possessed
binocular vision rather than 360 degree vision (much more ideal for spotting prey), they became
prime targets for predators. This increased predation led to them developing another trait that
would come to define them: group living, and complex social behaviors. As our text states, “the
chances of escaping [predators] is much greater for animals that live in groups where there are
several eyes looking about”. (Robert Jurmaine, Lynne Kilgore and Wendy Trevathan. Human
Origins: Evolution and Diversity. Wadsworth Cenage Learning, 2012, page 161). It would only stand
to reason then, that as primate’s social behaviors become more complex, the need for a greater
brain size increases accordingly. So indirectly, it was our eyesight that led to our intelligence.
In regards to the content of the film, I’ve got to say that I find no issue with really any of it. Each
of my sources backed or elaborated on each of the claims made. One article discussed in greater
detail the development of eye spot to complex vertebrate eye, and gave several examples of
organisms that still use simple eye spots: snails, scallops, and jellyfish are all modern examples.
(Learn Genetics, Eye Evolution, University of Utah Health and Sciences, 2014) But no
conflicting or new information was given.
Another article did take umbrage with the notion that all eyes evolved independently, however,
its counterargument was little more than, ‘all things are made up of the same root materials,
therefore eyes all come from the same source’, which seemed to me to be pretty self-explanatory.
(Carl Zimmer, How the Eye Evolved, New York Academy of Sciences Magazine, 2009)
Even our book largely agrees in regards to how primates evolved their eyes. To quote, “In a
complex, three-dimensional environment with uncertain footholds, acute color vision with depth
perception is, for obvious reasons, extremely beneficial.”( Robert Jurmaine, Lynne Kilgore and
Wendy Trevathan. Human Origins: Evolution and Diversity. Wadsworth Cenage Learning, 2012, page
126). This is, almost verbatim, exactly what the documentary was getting at.
Having nothing more to say, I think I will wrap this up here. It’s pretty apparent that eyes are a
big deal – one of nature’s biggest deals to be frank. I set out to discover just how nature could’ve
developed one of the most complex, delicate, diverse and essential appendages known, and I feel
pretty satisfied in the answers that our researchers were able to provide. Obviously, there are
gaps in knowledge and remaining questions – there will always be to some extent. What’s
important is we’ve pieced together the big picture. It’ll be up to future generation to fill in the
gaps.
WORKS CITED:
1) (Evolution: How the Eyes Evolved, Kurt Tondorf, Stephanie Angelides, Shelley Schulze,
Larry Engel, 2008)
2) (Carl Zimmer, How the Eye Evolved, New York Academy of Sciences Magazine, 2009)
3) (Learn Genetics, Eye Evolution, University of Utah Health and Sciences, 2014)
4) (Robert Jurmaine, Lynne Kilgore and Wendy Trevathan. Human Origins: Evolution and
Diversity. Wadsworth Cenage Learning, 2012, pages 126, 161)