Joined: May 2002
Put your favorite examples here!
Discussed on Evolving Inventions:
Before I attempt to answer your question, John, I would like to try and narrow down the exact, final, definitive definition of "inventive solution" in TRIZ-terms. The best I can seem to find are terms like "non-routine" and "resolving a technical contradiction", which help a bit but are difficult to apply.
Is there perhaps an authoritative quote you could post that would constitute the best-available definition?
Perhaps (especially since you focused on morphological evolution in your reply) answering the following would help:
Regarding morphology/development, would the following set of stages, if evolved through, constitute an "inventive" or "routine" solution:
1) Start with segmented metazoan.
2) Duplicate a segment (e.g. the corresponding Hox gene is serially duplicated). Critter now has an extra segment somewhere in the middle (say, 5 instead of 4) and corresponding pair of legs, etc., that go with the segment.
3) Repeat step 2 a number of times (e.g., selection for larger body size retains these duplications)
4) Once there are a fair number of segments, mutation and selection modify one or several of the more forward pairs, e.g. to improve prey capture or food-chewing or substrate/mate clasping (large number of possibilities here, lots of arthropods have these kinds of specializations).
Below is a slightly less abstract case (in arthropods, but dealing with the origin of a novel structure not from legs but from another structure). Would we have a novel or routine kind of solution here?
Proc Natl Acad Sci U S A 2002 Apr 16;99(8):5498-502
[which is free online I think]
Origin of a complex key innovation in an obligate insect-plant mutualism.
Pellmyr O, Krenn HW.
Evolutionary key innovations give organisms access to new ecological resources and cause rapid, sometimes spectacular adaptive radiation. The well known obligate pollination mutualism between yuccas and yucca moths is a major model system for studies of coevolution, and it relies on the key innovation in the moths of complex tentacles used for pollen collecting and active pollination. These structures lack apparent homology in other insects, making them a rare example of a novel limb. We performed anatomical and behavioral studies to determine their origin and found evidence of a remarkably simple mechanism. Morphological analyses of the tentacles and adjacent mouthparts in pollinators and closely related taxa showed that the tentacle appears abruptly in female pollinating yucca moths. Several morphological synapomorphies between the galeae, which constitute the characteristic lepidopteran proboscis, and the tentacle suggest that the tentacle evolved quickly through expression of the genetic template for the galea at an apical growth bud on the first segment of the maxillary palp. Behavioral data indicate that tentacle and proboscis movements are controlled by a shared hydraulic extension mechanism, thus no new mechanism was needed for tentacle function. Known developmental paths from other insects can explain the origin of this sex-specific key innovation in a few steps.
Other relevant articles:
J Exp Zool 2003 Feb 15;295B(1):1-11 Related Articles, Links
Hox genes as synchronized temporal regulators: Implications for morphological innovation.
Department of Biological Sciences, University of Windsor, Windsor, Ontario, N9B 3P4, Canada.
In vertebrates, clusters of Hox genes express in a nested and hierarchical fashion to endow the embryo's segments with discrete identities. Later in development, members of the same gene family are employed again to pattern the limb, intestinal, and reproductive systems. A careful analysis of the morphologies of Hox mutant mice suggests that the genes provide qualitatively different cues during the specification of segments than they do during the development of more recently derived structures. In addition to the regulatory differences noted by others, the activity of Hox genes during specification of the vertebrate metameres in some recent deletion experiments is inconsistent with a role for them as strictly spatial determinants. On the contrary, the phenotypes observed are suggestive of a role for them as elements of a generic time-keeping mechanism. By contrast, the specification of more recent evolutionary structures appears to be more spatial and gene-specific. These differences in role and effect may suggest some simple mechanisms by which the Hox clusters operate, and rules by which gene networks can be diverted to create new structures over the course of evolution. Specific predictions and experiments are proposed. J. Exp. Zool. (Mol. Dev. Evol.) 295B:1-11, 2003. Copyright 2003 Wiley-Liss, Inc.
Curr Biol 2002 Oct 1;12(19):1711-6
Diverse adaptations of an ancestral gill: a common evolutionary origin for wings, breathing organs, and spinnerets.
Damen WG, Saridaki T, Averof M.
Institute for Genetics, University of Cologne, Weyertal 121, D-50931, Koln, Germany.
Changing conditions of life impose new requirements on the morphology and physiology of an organism. One of these changes is the evolutionary transition from aquatic to terrestrial life, leading to adaptations in locomotion, breathing, reproduction, and mechanisms for food capture. We have shown previously that insects' wings most likely originated from one of the gills of ancestral aquatic arthropods during their transition to life on land. Here we investigate the fate of these ancestral gills during the evolution of another major arthropod group, the chelicerates. We examine the expression of two developmental genes, pdm/nubbin and apterous, that participate in the specification of insects' wings and are expressed in particular crustacean epipods/gills. In the horseshoe crab, a primitively aquatic chelicerate, pdm/nubbin is specifically expressed in opisthosomal appendages that give rise to respiratory organs called book gills. In spiders (terrestrial chelicerates), pdm/nubbin and apterous are expressed in successive segmental primordia that give rise to book lungs, lateral tubular tracheae, and spinnerets, novel structures that are used by spiders to breathe on land and to spin their webs. Combined with morphological and palaeontological evidence, these observations suggest that fundamentally different new organs (wings, air-breathing organs, and spinnerets) evolved from the same ancestral structure (gills) in parallel instances of terrestrialization.
A detailed review of the origin of feathers:
Q Rev Biol 2002 Sep;77(3):261-95
The evolutionary origin and diversification of feathers.
Prum RO, Brush AH.
Department of Ecology and Evolutionary Biology, and Natural History Museum, University of Kansas, Lawrence, Kansas 66045, USA. firstname.lastname@example.org
Progress on the evolutionary origin and diversification of feathers has been hampered by conceptual problems and by the lack of plesiomorphic feather fossils. Recently, both of these limitations have been overcome by the proposal of the developmental theory of the origin of feathers, and the discovery of primitive feather fossils on nonavian theropod dinosaurs. The conceptual problems of previous theories of the origin of feathers are reviewed, and the alternative developmental theory is presented and discussed. The developmental theory proposes that feathers evolved through a series of evolutionary novelties in developmental mechanisms of the follicle and feather germ. The discovery of primitive and derived fossil feathers on a diversity of coelurosaurian theropod dinosaurs documents that feathers evolved and diversified in nonavian theropods before the origin of birds and before the origin of flight. The morphologies of these primitive feathers are congruent with the predictions of the developmental theory. Alternatives to the theropod origin of feathers are critique and rejected. Hypotheses for the initial function of feathers are reviewed. The aerodynamic theory of feather origins is falsified, but many other functions remain developmentally and phylogenetically plausible. Whatever their function, feathers evolved by selection for a follicle that would grow an emergent tubular appendage. Feathers are inherently tubular structures. The homology of feathers and scales is weakly supported. Feathers are composed of a suite of evolutionary novelties that evolved by the duplication, hierarchical organization, interaction, dissociation, and differentiation of morphological modules. The unique capacity for modular subdivision of the tubular feather follicle and germ has fostered the evolution of numerous innovations that characterize feathers. The evolution of feather keratin and the molecular basis of feather development are also discussed.
Evol Dev 2002 Nov-Dec;4(6):459-99
Hox genes and the evolution of the arthropod body plan.
Hughes CL, Kaufman TC.
Howard Hughes Medical Institute, Department of Biology, Indiana University, Bloomington, IN 47405, USA.
In recent years researchers have analyzed the expression patterns of the Hox genes in a multitude of arthropod species, with the hope of understanding the mechanisms at work in the evolution of the arthropod body plan. Now, with Hox expression data representing all four major groups of arthropods (chelicerates, myriapods, crustaceans, and insects), it seems appropriate to summarize the results and take stock of what has been learned. In this review we summarize the expression and functional data regarding the 10 arthropod Hox genes: labial proboscipedia, Hox3/zen, Deformed, Sex combs reduced, fushi tarazu, Antennapedia, Ultrabithorax, abdominal-A, and Abdominal-B. In addition, we discuss mechanisms of developmental evolutionary change thought to be important for the emergence of novel morphological features within the arthropods.
Philos Trans R Soc Lond B Biol Sci 1995 Sep 29;349(1329):313-9
Hox genes and the evolution of diverse body plans.
Wellcome/CRC Institute and Department of Genetics, Cambridge, U.K.
Homeobox genes encode transcription factors that carry out diverse roles during development. They are widely distributed among eukaryotes, but appear to have undergone an extensive radiation in the earliest metazoa, to generate a range of homeobox subclasses now shared between diverse metazoan phyla. The Hox genes comprise one of these subfamilies, defined as much by conserved chromosomal organization and expression as by sequence characteristics. These Hox genes act as markers of position along the antero-posterior axis of the body in nematodes, arthropods, chordates, and by implication, most other triploblastic phyla. In the arthropods this role is visualized most clearly in the control of segment identity. Exactly how Hox genes control the structure of segments is not yet understood, but their differential deployment between segments provides a model for the basis of segment diversity. Within the arthropods, distantly related taxonomic groups with very different body plans (insects, crustaceans) may share the same set of Hox genes. The expression of these Hox genes provides a new character to define the homology of different body regions. Comparisons of Hox gene deployment between insects and a branchiopod crustacean suggest a novel model for the derivation of the insect body plan.
Annu Rev Cell Dev Biol 2002;18:53-80
Gene co-option in physiological and morphological evolution.
True JR, Carroll SB.
Department of Ecology and Evolution, State University of New York at Stony Brook, Stony Brook, New York 11794-5245, e-mail: email@example.com
Co-option occurs when natural selection finds new uses for existing traits, including genes, organs, and other body structures. Genes can be co-opted to generate developmental and physiological novelties by changing their patterns of regulation, by changing the functions of the proteins they encode, or both. This often involves gene duplication followed by specialization of the resulting paralogous genes into particular functions. A major role for gene co-option in the evolution of development has long been assumed, and many recent comparative developmental and genomic studies have lent support to this idea. Although there is relatively less known about the molecular basis of co-option events involving developmental pathways, much can be drawn from well-studied examples of the co-option of structural proteins. Here, we summarize several case studies of both structural gene and developmental genetic circuit co-option and discuss how co-option may underlie major episodes of adaptive change in multicellular organisms. We also examine the phenomenon of intraspecific variability in gene expression patterns, which we propose to be one form of material for the co-option process. We integrate this information with recent models of gene family evolution to provide a framework for understanding the origin of co-optive evolution and the mechanisms by which natural selection promotes evolutionary novelty by inventing new uses for the genetic toolkit.
In fact, right now we are living through the merging of developmental biology with the modern synthesis, e.g.:
Toward a new synthesis: population genetics and evolutionary developmental biology.
Johnson NA, Porter AH.
Department of Entomology and Program in Organismic and Evolutionary Biology, University of Massachusetts, Amherst 01003, USA.
Despite the recent synthesis of developmental genetics and evolutionary biology, current theories of adaptation are still strictly phenomenological and do not yet consider the implications of how phenotypes are constructed from genotypes. Given the ubiquity of regulatory genetic pathways in developmental processes, we contend that study of the population genetics of these pathways should become a major research program. We discuss the role divergence in regulatory developmental genetic pathways may play in speciation, focusing on our theoretical and computational investigations. We also discuss the population genetics of molecular co-option, arguing that mutations of large effect are not needed for co-option. We offer a prospectus for future research, arguing for a new synthesis of the population genetics of development.