Evolution: Education and Outreach

by Lamb, Trevor D.; Pugh, Edward N.; Collin, Shaun P.

In his considerations of “organs of extreme perfection,” Charles Darwin described the evidence that would be necessary to support the evolutionary origin of the eye, namely, demonstration of the existence of “numerous gradations” from the most primitive eye to the most perfect one, where each such tiny change had provided a survival advantage (however slight) to the organism possessing the subtly altered form. In this paper, we discuss evidence indicating that the vertebrate eye did indeed evolve through numerous subtle changes. The great majority of the gradual transitions that did occur have not been preserved to the present time, either in the fossil record or in extant species; yet clear evidence of their occurrence remains. We discuss the remarkable “eye” of the hagfish, which has features intermediate between a simple light detector and an image-forming camera-like eye and which may represent a step in the evolution of our eye that can now be studied by modern methods. We also describe the important clues to the evolutionary origin of the vertebrate eye that can be found by studying the embryological development of our own eye, by examining the molecular genetic record preserved in our own genes and in the genes of other vertebrates, and through consideration of the imperfections (or evolutionary “scars”) in the construction of our eye. Taking these findings together, it is possible to discuss in some detail how the vertebrate eye evolved.

DOI: 10.1007/s12052-008-0091-2
Online Date: 9/30/2008
Print publication date: 10/1/2008
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by Petto, Andrew J.; Mead, Louise S.

Despite data and theory from comparative anatomy, embryology, molecular biology, genomics, and evolutionary developmental biology, antievolutionists continue to present the eye as an example of a structure too complex to have evolved. They stress what we have yet to explain about the development and evolution of eyes and present incomplete information as evidence that evolution is a “theory in crisis.” An examination of the evidence, however, particularly evidence that has accumulated in the twentieth and twenty-first centuries, refutes antievolutionists’ claims. The distribution of eyes in extant organisms, combined with what we now know about the control of eye development across diverse groups of organisms, provides significant evidence for the evolution of all major components of the eye, from molecular to morphological, and provides an excellent test of predictions based on common ancestry.

DOI: 10.1007/s12052-008-0082-3
Online Date: 9/27/2008
Print publication date: 10/1/2008
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by Thanukos, Anastasia

Anyone who has skimmed a high school biology textbook will be familiar with the iconic examples of homology that seem inseparable from any explanation of the term: the limb structure of four-legged animals, the human tailbone and the more elaborate tail of monkeys, and the remarkable similarities among the embryological development of fish, birds, and humans. These same examples make their way from edition to edition, along with the classic illustration of an analogous structure: the wings of butterflies, birds, and bats. But is that really all there is to say about homologies and analogies? Several articles in this issue discuss these concepts more deeply in the context of eye evolution (Gregory 2008; Oakley and Pankey 2008; Piatigorsky 2008). Homologies and analogies, it seems, are not a black and white issue—especially when it comes to vision.

DOI: 10.1007/s12052-008-0080-5
Online Date: 9/26/2008
Print publication date: 10/1/2008
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by Piatigorsky, Joram

Did the diversity of lens-containing eyes evolve from one ancestral eye (monophyletic evolution) or from multiple, independently derived eyes (polyphyletic evolution)? Monophyletic evolution would make diverse eyes homologous (inherited similarities from a common ancestor); polyphyletic evolution would make eyes homoplasious (independently acquired similarities). Historically, anatomical and developmental differences among eyes of different species favored homoplasy; however, recent molecular data indicating that all eyes employ a similar cascade of transcription factors (proteins regulating gene expression) for development have suggested homology. Comparative studies on invertebrates and vertebrates suggest that the use of common networks of developmental transcription factors may be due to parallel evolution, a form of homoplasy by independent recruitments of similar genes and transcriptional networks. Remarkably, the photoreceptors of lens-containing jellyfish eyes have ciliary photoreceptors, like vertebrate photoreceptors, and apparently employ a vertebrate phototransduction system (linked biochemical processes converting light into nervous electrical impulse), consistent with parallel evolution between jellyfish and vertebrate eyes. Finally, the major proteins conferring the lens optical properties—the crystallins—were recruited by a gene-sharing process (the addition of a new gene function without loss of the original function) from various stress proteins and common metabolic enzymes in different species by convergent mutations (derived independently, not related by common ancestry) in their promoters (gene regulatory sequences) leading to high lens expression. Thus, the data indicate that homology or homoplasy of diverse eyes depends upon the level of analysis.

DOI: 10.1007/s12052-008-0077-0
Online Date: 9/26/2008
Print publication date: 10/1/2008
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by Serb, Jeanne M.; Eernisse, Douglas J.

For over 100 years, molluscan eyes have been used as an example of convergent evolution and, more recently, as a textbook example of stepwise evolution of a complex lens eye via natural selection. Yet, little is known about the underlying mechanisms that create the eye and generate different morphologies. Assessing molluscan eye diversity and understanding how this diversity came about will be important to developing meaningful interpretations of evolutionary processes. This paper provides an introduction to the myriad of eye types found in molluscs, focusing on some of the more unusual structures. We discuss how molluscan eyes can be applied to the study of evolution by examining patterns of convergent and parallel evolution and provide several examples, including the putative convergence of the camera-type eyes of cephalopods and vertebrates.

DOI: 10.1007/s12052-008-0084-1
Online Date: 9/25/2008
Print publication date: 10/1/2008
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by Horenstein, Sidney

DOI: 10.1007/s12052-008-0078-z
Online Date: 9/25/2008
Print publication date: 10/1/2008
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by Wycoff, Mick

DOI: 10.1007/s12052-008-0079-y
Online Date: 9/25/2008
Print publication date: 10/1/2008
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by Eldredge, Niles

DOI: 10.1007/s12052-008-0074-3
Online Date: 9/20/2008
Print publication date: 10/1/2008
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by Cronin, Thomas W.; Porter, Megan L.

The Crustacea contain an amazing, and often (to humans) bizarre, array of visual designs. This diversity includes many different examples of both simple and compound eyes, each with standard or uniquely crustacean features. In this review, we focus on the anatomical variation, optical principles, and molecular diversity of crustacean compound eyes to illustrate how the complicated structures involved in vision are adapted for particular environments. Using this knowledge as a starting point, and considering what is known of crustacean evolution overall, we present the most recent ideas of how crustacean compound eyes have evolved and show how eyes that are based on fundamentally different optical principles can in fact be derived from each other and thus be closely related through common descent.

DOI: 10.1007/s12052-008-0085-0
Online Date: 9/20/2008
Print publication date: 10/1/2008
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by Eldredge, Niles

DOI: 10.1007/s12052-008-0070-7
Online Date: 9/19/2008
Print publication date: 10/1/2008
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