Book of the Month June 2005

This months book of the month is "In the Blink of an Eye" by Andrew Parker. This is Parkers take on the Cambrian "Explosion*," an incredible event that occured roughly 540 million years ago. This event resulted in all of the phyla of animals now seen on Earth, and one or two that have subsequently gone extinct. No one really knows why it happened, but Parker thinks he might be on to something...

*(Please note that my use of quotation marks around the word explosion is because of my feelings about the term itself, which is a bit misleading. What people tend to think of as an immediate event, like an explosion, in this instance took a few million years, maybe around ten million or so. While this is an extraordinarily long amount of time for creatures such as ourselves, which live to be about 80 years old or so, geologically, this was fairly rapid, hence the name "Cambrian Explosion.")

Evolution's Big Bang

Parker begins this chapter talking a bit about his interests, the things that drew him to become a biologist. The impetus for this book, which is ultimately about the evolution of eyesight, began with a curious attraction to cuttlefish eyes, which is in ways similar to the human eye. He then describes the basics of the variety of life, and explains the Cambrian "Explosion." Then, he outlines his intent with the book, giving a brief description of the following chapters, and mentioning his goal for each one, which he would like to use to piece together what he concludes as the solution to the mystery behind the most puzzling conundrum in the history of life. The very thing that spurred the notion of the Cambrian "Explosion" itself was a unique fossil find in Canada, the infamous Burgess Shale. The Burgess Shale holds an untold number of exquisitely preserved fossils from right on the brink of the crucial period in animal diversity. The Burgess Shale presented the field of paleontology with a massive amount of fossils and new species that hadn't even been dreamed of prior to its discovery. This fossil quarry would be the driving factor in what we call the Cambrian "Explosion." Parker does the reader a bit of justice in attempting to provide some of the explanations for the "Explosion" that have been presented, but, he concludes, they don't do an adequate job of explaining, which is why he chose to write this book.

The Virtual Life of Fossils

An important basis for this book, and the study of anything related to the Cambrian "Explosion" requires a look at fossils. Here, Parker discusses the usefulness of fossils, what they can tell us, and more importantly what they can help us figure out. He starts off by giving a bit of the history of fossils, and then tells us what paleontologists can do with the fossils they're given. One important aspect to fossils is recreating from them what we think an organism may have looked like, given the preserved remains and a knowledge of what kind of organism it is. This is more easily done with younger fossils, because the younger fossils look more closely like the things we can still find around today. For example, although we've found preserved remains of mastodons and mammoths, they're still remarkably similar to their modern day descendants, the elephants, so a reasonable guess to their habits and appearance can be deduced from elephants. This gets harder with older fossils, because they tend to move farther from familiarity the older they get. This is the case with Cambrian fossils, because many of the organisms that are found in Cambrian-age fossil sites are completely alien to us. This makes placing them in the family tree for life even more difficult, but some work has been done to figure things out...

The Infusion of Light

This chapter discusses the importance of light, which is a central basis for Parkers contention for the Cambrian "Explosion." He first discusses (briefly) the history of light in science, and then goes into discussing the role of light and color. Color, in the form of pigments and chromatophores, plays a vital part in the every day goings one of many orgniams. In fact, it is this vitality that Parker hopes to ingrain into the reader, and he contends that light is one of the most important factors in evolution. He builds on this point by discussing several animals which use color in different ways. Some animals use it for attracting mates, some use it for fending off attackers, but that they use it at all is significant to Parker...

When Darkness Descends

A problem with Victorian scientists, Parker begins in this chapter, is that they had a bias for diurnal (daytime) organisms, and did not describe much about the life during the nighttime. There is a reason for this: our eyes don't see well in the dark. This is why we invent things like nightvision goggles which collect the available light and help us see in the dark. But there are living things in the nighttime sky, and light, even though its absent (at least directly from the Sun) still plays a role in their livelihood. Parker examines how nocturnal animals, as well as cave animals, who do not receive any light at all, cope with the light they have (or don't have) and the part that light has played in their evolution...

Light, Time and Evolution

So, how does light play a role in evolution? In many diverse ways, thats how. Here, Parker tells us about a discovery he made studying a very comon group of "seed-pod" shrimp. While cutting them up for study, he noted a flash of green under the miscroscope, and found it unusual. He showed it to others, and then discovered that many species had similar flashes, some green, some blue, others with other colors. What was the point of these flashes? Sex, thats what!

Colour in the Cambrian

What helped make this flashes of light for the seed-pod shrimp in the previous chapter were small little structures that behaved in a similar fashion as diffraction gratings used in physics, which can, themselves, affect and produce different colors. Seed-pod shrimp aren't the only animals that have them, however, and there is some evidence that some Cambrian animals (seed-pod shrimp were present in the Cambrian as well) had structures like the diffraction gratings. This might imply that they might have been able to produce the same sort of color displays that our present day seed-pod shrimp do. Could the Cambrian seas have been filled with flashes of color?

The Making of a Sense

Parker has set up the pitch for his theory in the preceeding chapters, and in this one, he takes the reader into the purpose and creation of eyesight. He describes what it is to see, what an eye is, what vision is. What this chapter is really about is the evolution of the eye, from the first photosensitive cell to the human eye. Parker goes through the step-by-step process of how scientists think the eye evolved.

The Killer Instinct

A very compelling force in evolution is the arms race, especially in the animal kingdom. The predator-prey relationship is a very fertile area within which evolution produces many different results, from camouflage to speed, to claws, spikes, horns and what have you. The importance of predation to Parkers story, however, is that there is a marked change in how predation is done, something that changed right around the same time as the Cambrian "Explosion." The trend goes from passive predation, which generally involves feeling around for your prey, and if you feel it, you can eat it, to active predation, which includes looking for, hunting down, and trapping your prey.

The Solution

Parker now puts chapters 7 and 8 together... the emergence of eyesight for predation. It is the emergence of eyesight, Parker contends, which helped drive the massive "explosion" of lifeforms seen in the Cambrian. Animals have gone from sightless passive predation, and bodies were soft and not well preserved, to having eyes that could focus, track, and most importantly see prey. This crucial transition from blindness to sight might have induced the development of armor, hard-shell protection that might give you an edge after being spotted by a predator. Parker argues convincingly that this codevelopment and occurence must be more than just coincidence.

End of Story?

Parker now has a name for this suggestion - the Light Switch Theory - and presents it to his peers. It seemed to answer many questions, but he points out that one question remains unanswered by his theory: why eyes? His Light Switch Theory does have merit, but there might have been other triggers to the Cambrian "Explosion," some of which he presents here. Maybe these alternatives had something to do with the course of evolution on Earth, perhaps not, but they are worth mentioning.

Summary

This book is an easy read. It is simply absorbed, well thought out, and presented in a way that makes sense to the reader. Parker very deliberately sets up his chapters, something he points out at the very beginning, in a structure that makes a very compelling argument. I am not sure how well this theory has been maintained in the literature, and how it goes among peer review, but it does seem to be an interesting idea. Parker's writing style is easy to follow, and this is not a difficult read by any means. There are some technical terms that might be confusing, if the reader isn't already aware of them, but nothing too difficult or hard to figure out. I would highly recommend this book.