by Novella, Steven

The human eye is an excellent example of suboptimal bottom-up design resulting from the constraints of evolutionary historical contingency. The resulting suboptimal optics manifests in a number of medical ophthalmological disorders.

DOI: 10.1007/s12052-008-0092-1
Online Date: 10/25/2008
Print publication date: 10/1/2008
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by Espinasa, Monika; Espinasa, Luis

When we teach evolution to our students, we tend to focus on “constructive” evolution, the processes which lead to the development of novel or modified structures. Most biology students are familiar with the subjects of finches’ beaks, giraffes’ necks, and hair in mammals. Of course, there is nothing inherently wrong with a constructivist approach to teaching evolution, but if it is our only focus, we may overlook the flip side of the coin. By the flip side of the coin, of course, we are referring to regressive evolution: the loss or degeneration of a trait. Regressive evolution does not often make its way into biology textbooks, but it is of great relevance nonetheless. In all likelihood, when a new trait evolves or an existing one is modified, something is sacrificed in return. In order to develop a flipper, a marine mammal must sacrifice individual digits. You may be familiar with one or more of the following familiar characters lost through regressive evolution: teeth in birds, scales in mammals, and tails in higher primates. For aficionados of cave biology like us, one of the most interesting examples of regressive evolution concerns cave fish: Why do cave fish lose their eyes?

DOI: 10.1007/s12052-008-0094-z
Online Date: 10/23/2008
Print publication date: 10/1/2008
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by Oakley, Todd H.; Pankey, M. Sabrina

Eyes provide a rich narrative for understanding evolution, having attracted the attention of preeminent scientists and communicators alike. Until recently, this narrative has focused primarily on the evolution of eye structure and far less on biochemistry or genetics. Although eye biochemistry was once likened to an unknown “black box;” the flood of discoveries in biochemistry is now allowing an increasingly detailed understanding of the processes involved in vision. As a result, evolutionary comparative (“tree-thinking”) analyses that use these data currently allow a new and still unfolding narrative, both richer in detail and more comprehensive in scope. Rather than toppling evolutionary theory by finding irreducibly complex molecular machines, eye evolution provides detailed accounts of how natural processes tinker with existing genetic components, duplicating and recombining them, to yield complex, intricate, and highly functional eyes. Understanding the new biochemical narrative is critical for researchers and teachers alike, in order to answer anti-evolutionist claims, and to provide an up-to-date account of the state of knowledge on the subject of eye evolution.

DOI: 10.1007/s12052-008-0090-3
Online Date: 10/23/2008
Print publication date: 10/1/2008
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by Eldredge, Gregory; Eldredge, Niles

DOI: 10.1007/s12052-008-0081-4
Online Date: 10/21/2008
Print publication date: 10/1/2008
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by Buschbeck, Elke K.; Friedrich, Markus

The visual organs of insects are known for their impressive evolutionary conservation. Compound eyes built from ommatidia with four cone cells are now accepted to date back to the last common ancestor of insects and crustaceans. In species as different as fruit flies and tadpole shrimps, the stepwise cellular patterning steps of the early compound eye exhibit detailed similarities implying 500 million years of developmental conservation. Strikingly, there is also a cryptic diversity of insect visual organs, which gives proof to evolution’s versatility in molding even the most tenacious structures into something new. We explore this fascinating aspect in regard to the structure and function of a variety of different insect eyes. This includes work on the unique compound–single-chamber combination eye of twisted-winged insects and the bizarre evolutionary trajectories of specialized larval eyes in endopterygote insects.

DOI: 10.1007/s12052-008-0086-z
Online Date: 10/18/2008
Print publication date: 10/1/2008
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by Young, Gavin C.

Evidence of detailed brain morphology is illustrated and described for 400-million-year-old fossil skulls and braincases of early vertebrates (placoderm fishes). Their significance is summarized in the context of the historical development of knowledge of vertebrate anatomy, both before and since the time of Charles Darwin. These ancient extinct fishes show a unique type of preservation of the cartilaginous braincase and demonstrate a combination of characters unknown in other vertebrate species, living or extinct. The structure of the oldest detailed fossil evidence for the vertebrate eye and brain indicates a legacy from an ancestral segmented animal, in which the braincase is still partly subdivided, and the arrangement of nerves and muscles controlling eye movement was intermediate between the living jawless and jawed vertebrate groups. With their unique structure, these placoderms fill a gap in vertebrate morphology and also in the vertebrate fossil record. Like many other vertebrate fossils elucidated since Darwin’s time, they are key examples of the transitional forms that he predicted, showing combinations of characters that have never been observed together in living species.

DOI: 10.1007/s12052-008-0087-y
Online Date: 10/18/2008
Print publication date: 10/1/2008
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by Zimmer, Carl

DOI: 10.1007/s12052-008-0089-9
Online Date: 10/16/2008
Print publication date: 10/1/2008
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by Oakley, Todd H.

DOI: 10.1007/s12052-008-0093-0
Online Date: 10/16/2008
Print publication date: 10/1/2008
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by Gregory, T. Ryan

The origin of complex biological structures has long been a subject of interest and debate. Two centuries ago, natural explanations for their occurrence were considered inconceivable. However, 150 years of scientific investigation have yielded a conceptual framework, abundant data, and a range of analytical tools capable of addressing this question. This article reviews the various direct and indirect evolutionary processes that contribute to the origins of complex organs. The evolution of eyes is used as a case study to illustrate these concepts, and several of the most common misconceptions about complex organ evolution are discussed.

DOI: 10.1007/s12052-008-0076-1
Online Date: 10/10/2008
Print publication date: 10/1/2008
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by Horenstein, Sidney

Cities large and small have a treasure trove of building stones both local as well as imported from various regions of the country as well as foreign sources. Many of them contain fossils which are easily available for teachers to utilize for class field trips. For some areas guidebooks exist which are listed in the attached appendix. Even for localities where no guidebook exists these published guides can be helpful especially if they are illustrated. Field trips are a useful learning tool and teachers are encouraged to create various lesson plans utilizing this generally unrecognized resource.

DOI: 10.1007/s12052-008-0075-2
Online Date: 10/9/2008
Print publication date: 10/1/2008
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