We have discovered unexpected similarities between a novel and characteristic wing organ in an ex... more We have discovered unexpected similarities between a novel and characteristic wing organ in an extinct biting midge from Baltic amber, Eohelea petrunkevitchi, and the surface of a dipteran's compound eye. Scanning electron microscope images now reveal vestigial mechanoreceptors between the facets of the organ. We interpret Eohelea's wing organ as the blending of these two developmental systems: the formation and patterning of the cuticle in the eye and of the wing.
Page 1. Biological Journal of the 1,innean Sociep (1982), 17: 23-37 Turning points in Darwin'... more Page 1. Biological Journal of the 1,innean Sociep (1982), 17: 23-37 Turning points in Darwin's life KEITH STEWART THOMSON* AND STAN P. RACHOOTINt Department of Biology, Yale University, New Haven, Connecticut 06520, USA . ...
ABSTRACT 'Three requirements of evolution are persistence with chang e, internally cohe s ive ind... more ABSTRACT 'Three requirements of evolution are persistence with chang e, internally cohe s ive individua l s of limi t ed dura t ion, and interaction with environment. W e recas t th es e proper t i es in mega evolutionary terms. Harologous structures persist over geological t ime as th ey evo lve in f orm and func t ion . Spec ies, which arise through a greater or lesser genetic r evolution, behave as individuals. The interac t ion of genes and environments--development--under lies bo th the origin of species and the continuity of harologies. The properties of epigenetics --self assemb ly , feedback, a lternative pathways to the sane devel opmental end, canpensati on for the inevitable irregularities of development--allow a redefinition of gene t ic revol ution in terms of the establishment of new, stab le developmental patterns : a typological r esult produced in ac ceptably popul ati ona l ways . Harologues, s imi larly , are the products of evo lving ep igene tic sub-systems. Al though developmental systems retain ancestral potentials that renain unexpressed for tens of millions of years, such potentials are so burdened with other developmental pathways built upon them that they hold little promise for evolutionary change. But where a recent developmental change ha s occurred, no such "buf f ering" exists . As errors oc cur , sane will be ep igenetically acconm:>dated and , if adap tive, gene t i cally assimilated . Thes e are the quanta of evo lution . If a r ecent adaptive breakthrough has oc curred, i t wi ll be " suppor t ed" at first by interacting ep igenetic sub-systems. The poorly canalized epigenetic system roost; closely associated with the new adaptation will be under intense selection to build up an epigenetic environment that assures the predictable expression of the new trait . Until this happens, fur ther " exper imen ts" along the l ines of t he initial change can occur and be assimilated . Depend ing on eco logical mi lieu, t his i s the stuff of adaptive r adiation , evo l u t i onary trends, or a llanetri c change. Speciation, which can occur without any adaptive chang e, is th e result of analogous changes in the ep igenetic systems responsible for mate r ecogni tion . We accept the neo-Darwinian reliance on natural selection acting in populations. But we choose to concentrate on i ts action on developmental processes, rather than on traits , the obvious and experimentally tractable end -products of such processes. The normal features of epigenet ics f ortui tousl y l ay down the lines of l ea st r esistance to evo l utionary change. We find ours elves l ooking a t an intrinsic and emergent s i de to evo lution, a view that in the past was held, on s imilar gen er a l grounds, by Bateson, Goldschnidt, and Waddington . The story of evolution i s perhaps less the warfare of selfish genes than the YX>rking out of the potentials of selfless epigenes.
CHARLES DARWIN'S NATURAL SELECTION BEING THE SECOND PART OF HIS BIG SPECIES BOOK WRITTEN FRO... more CHARLES DARWIN'S NATURAL SELECTION BEING THE SECOND PART OF HIS BIG SPECIES BOOK WRITTEN FROM 1856 TO 1858 EDITED FROM MANUSCRIPT BY RC STAUFFER University of Wisconsin, Madison With the(iiii<les to the texts. Collation with the first ...
We have discovered unexpected similarities between a novel and characteristic wing organ in an ex... more We have discovered unexpected similarities between a novel and characteristic wing organ in an extinct biting midge from Baltic amber, Eohelea petrunkevitchi, and the surface of a dipteran's compound eye. Scanning electron microscope images now reveal vestigial mechanoreceptors between the facets of the organ. We interpret Eohelea's wing organ as the blending of these two developmental systems: the formation and patterning of the cuticle in the eye and of the wing.
Page 1. Biological Journal of the 1,innean Sociep (1982), 17: 23-37 Turning points in Darwin'... more Page 1. Biological Journal of the 1,innean Sociep (1982), 17: 23-37 Turning points in Darwin's life KEITH STEWART THOMSON* AND STAN P. RACHOOTINt Department of Biology, Yale University, New Haven, Connecticut 06520, USA . ...
ABSTRACT 'Three requirements of evolution are persistence with chang e, internally cohe s ive ind... more ABSTRACT 'Three requirements of evolution are persistence with chang e, internally cohe s ive individua l s of limi t ed dura t ion, and interaction with environment. W e recas t th es e proper t i es in mega evolutionary terms. Harologous structures persist over geological t ime as th ey evo lve in f orm and func t ion . Spec ies, which arise through a greater or lesser genetic r evolution, behave as individuals. The interac t ion of genes and environments--development--under lies bo th the origin of species and the continuity of harologies. The properties of epigenetics --self assemb ly , feedback, a lternative pathways to the sane devel opmental end, canpensati on for the inevitable irregularities of development--allow a redefinition of gene t ic revol ution in terms of the establishment of new, stab le developmental patterns : a typological r esult produced in ac ceptably popul ati ona l ways . Harologues, s imi larly , are the products of evo lving ep igene tic sub-systems. Al though developmental systems retain ancestral potentials that renain unexpressed for tens of millions of years, such potentials are so burdened with other developmental pathways built upon them that they hold little promise for evolutionary change. But where a recent developmental change ha s occurred, no such "buf f ering" exists . As errors oc cur , sane will be ep igenetically acconm:>dated and , if adap tive, gene t i cally assimilated . Thes e are the quanta of evo lution . If a r ecent adaptive breakthrough has oc curred, i t wi ll be " suppor t ed" at first by interacting ep igenetic sub-systems. The poorly canalized epigenetic system roost; closely associated with the new adaptation will be under intense selection to build up an epigenetic environment that assures the predictable expression of the new trait . Until this happens, fur ther " exper imen ts" along the l ines of t he initial change can occur and be assimilated . Depend ing on eco logical mi lieu, t his i s the stuff of adaptive r adiation , evo l u t i onary trends, or a llanetri c change. Speciation, which can occur without any adaptive chang e, is th e result of analogous changes in the ep igenetic systems responsible for mate r ecogni tion . We accept the neo-Darwinian reliance on natural selection acting in populations. But we choose to concentrate on i ts action on developmental processes, rather than on traits , the obvious and experimentally tractable end -products of such processes. The normal features of epigenet ics f ortui tousl y l ay down the lines of l ea st r esistance to evo l utionary change. We find ours elves l ooking a t an intrinsic and emergent s i de to evo lution, a view that in the past was held, on s imilar gen er a l grounds, by Bateson, Goldschnidt, and Waddington . The story of evolution i s perhaps less the warfare of selfish genes than the YX>rking out of the potentials of selfless epigenes.
CHARLES DARWIN'S NATURAL SELECTION BEING THE SECOND PART OF HIS BIG SPECIES BOOK WRITTEN FRO... more CHARLES DARWIN'S NATURAL SELECTION BEING THE SECOND PART OF HIS BIG SPECIES BOOK WRITTEN FROM 1856 TO 1858 EDITED FROM MANUSCRIPT BY RC STAUFFER University of Wisconsin, Madison With the(iiii<les to the texts. Collation with the first ...
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