This is a revised edition with a new afterword by Daniel Dennett. The Extended Phenotype carries on from where The Selfish Gene takes off. It is a fascinating look at the evolution of life and natural selection. Dawkins's theory is that individual organisms are replicators that have extended phenotypic effects on society and the world at large, thus our genes have the ability to manipulate other individuals. A worldwide bestseller, this book has become a classic in popular science writing.
T h is c a n n ot be t he w h o le s t o r y, as C r ow p o i n ts o u t, b e c a u se s p e r ms h a ve b e en s h o wn to be c a p a b le of d e v e l o p i ng n o r m al tails w i t h o ut a ny c h r o m o s o m es at a l l. I n d e e d, t he w h o le s p e rm p h e n o t y pe s e e ms u s u a l ly to be u n d er t he c o n t r ol of t he d i p l o id g e n o t y pe of t he f a t h e r, n ot its o wn h a p l o id g e n o t y pe ( B e a t ty & G l u e c k s o h n W a e l s ch 1 9 7 2; see b e l o w ). ' T he effect of t he SD c h r o m o s o me on its h o m o l o g ue c a n n o t, t h e n, be s i m p ly to i n a c t i v a te s o me f u n c t i o n, b e c a u se no f u n c t i on is r e q u i r e d. SD m u st s o m e h ow i n d u ce its p a r t n er to c o m m it a p o s i t i ve a ct of s a b o t a g e .'
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S e g r e g a t i on d i s t o r t e rs p r o s p er w h en r a r e, b e c a u se t he c h a n c es a re
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W h en c o m m o n, t he d i s t o r t er t e n ds to o c c ur h o m o z y g o u s l y, a nd t h e r e f o re s a b o t a g es c o p i es of itself, m a k i ng t he o r g a n i sm v i r t u a l ly s t e r i l e. T he s t o ry is m o re c o m p l i c a t ed t h an this, b ut c o m p u t er s i m u l a t i o ns d e s c r i b ed by C r ow s u g g e st t h at a s t a b le p r o p o r t i on of s e g r e g a t i on d i s t o r t er g e n es w i ll be m a i n t a i n ed at a f r e q u e n cy s o m e w h at g r e a t er t h an w o u ld be a c c o u n t ed for by r e c u r r e nt m u t a t i on a l o n e. T h e re is s o me e v i d e n ce t h at this is so in r e al life. In o r d er to q u a l i fy as an o u t l a w, a s e g r e g a t i on d i s t o r t er m u st do h a rm to m o st of t he rest of t he g e n o m e, n ot j u st to its a l l e l e s. S e g r e g a t i on distorters
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E v en if t h ey d id n ot do this, t h e re is a m o re g e n e r al r e a s on for e x p e c t i ng t h e re to be s e l e c t i on at o t h er l o ci in f a v o ur of s u p p r e s s i ng t h em ( C r ow 1 9 7 9 ). T he a r g u m e nt n e e ds to be d e v e l o p ed s t a ge by s t a g e. F i r s t ly m a ny g e n e s, w h en c o m p a r ed w i th t h e ir a l l e l e s, h a ve s e v e r al p l e i o t r o p ic effects. L e w o n t in ( 1 9 7 4) g o es so far as to s p e ak of ' .. . t he u n d o u b t ed t r u th t h at e v e ry g e ne affects e v e ry c h a r a c t er .. .'. W h i le to c a ll this an ' u n d o u b t ed t r u t h' m ay b e, O u t l a ws and M o d i f i e rs 137 to p ut it m i l d l y, an e n t h u s i a s t ic e x a g g e r a t i o n, for my p u r p o s es I n e ed o n ly a s s u me t h at m o st n ew m u t a t i o ns h a ve s e v e r al p l e i o t r o p ic effects.
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