CONSIDERATIONS ON THE EVOLUTIONARY THEORY F . G . B r i e g e r A u g u s t , 1983 I t i s not my i n t e n t i o n t o p r e s e n t a d e t a i l e d h i s t o r y of the d e v e l o p m e n t of the t h e o r y of E v o l u t i o n as g e n e r a l l y f o r m u l a t e d t o d a y , b u t o n l y to p r e s e n t some s t e p s w h i c h have had s p e c i a l i m p o r t a n c e i n t h e p a s t o r w h i c h r e q u i r e now r e c o n s i d e r a t i o n . Some p o i n t s of v i e w a c c e p t e d as e s s e n t i a l i n t h e p a s t , owing t o f a c t s t h e n c o n s i d e r e d e v i d e n t , were not r a r e l y i n c l u d e d i n the g e n e r a l t h e o r y though sometimes h a v i n g r e s u l t e d from b i a s , e x a g e r a t i n g t h e i r i m p o r t a n c e w h i l e h a v i n g a c t u a l l y become w i t h o u t much i m p o r t a n c e , t h u s r e p r e s e n t i n g a n e c e s s a r y b a l l a s t o r dead w e i g h t .
Some m y t h o l o g i c a l c o n c e p t s about o r i g i n of l i f e or more s p e c i f i c a l l y of mankind, e x i s t e d probably i n many p a r t s of the w o r l d and have been a c c e p t e d by s t i l l
r a t h e r p r i m i t i v e i n d i g e n o u s p e o p l e . D u r i n g the m i d d l e a g e s , i d e a s of A r i s t o t e l e a n p h i l o s o p h y o r t h e b i b l i c a l c o n c e p t s were a c c e p t e d as r e p r e s e n t i n g t h e " t r u t h " . I n the m i d d l e of the 1 8t h c e n t u r y modern o r s c i e n t i f i c
r e a s o n i n g s t a r t e d i n t h e b i o l o g i c a l s c i e n c e s , and one c a n , from t h e n o n , d i s t i n g u i s h two p h a s e s of d e v e l o p m e n t of s c i e n t i f i c s t u d y of e v o l u t i o n . I n the f i r s t p h a s e the q u e s t i o n s of e v o l u t i o n as a p r o c e s s p r e d o m i n a t e d , w h i l e a f t e r i t s a c c e p t a n c e had s p r e a d more o r l e s s w i d e l y , t h e d i s c u s s i o n p a s s e d t o a s e c o n d p h a s e , t h e s t u d y of t h e e v o l u t i o n a r y m e c h a n i s m . Not i n f r e q u e n t l y b o t h p h a s e s a r e c a l l e d s u m m a r i l y " d a r w i n i s m " . A c t u a l l y ,
when DARWIN s t a r t e d h i s work and p u b l i s h e d the r e s u l t s , the h y p o t h e s i s of e v o l u t i o n as a p r o c e s s had been
a c c e p t e d by many s c i e n t i s t s , and DARWIN's c o n t r i b u t i o n d e a l t m a i n l y w i t h the e v o l u t i o n a r y m e c h a n i s m , though g r e a t l y c o n t r i b u t i n g t o s t r e n g t h e n s u p p o r t of the e v o l u t i o n a r y h y p o t h e s i s i n g e n e r a l . I n p r e p a r i n g t h e p r e s e n t paper the q u e s t i o n a r o s e w h i c h b i b l i o g r a p h i c a l r e f e r e n c e s s h o u l d be g i v e n out of t h e v a s t number of p u b l i c a t i o n s e x i s t i n g today t r e a t i n g e v o l u t i o n and c o n n e c t e d s u b j e c t s . S u c h c i t a t i o n s might h e l p t h e r e a d e r , b u t would u n d o u b t e d l y i n c r e a s e the s i z e of t h i s p a p e r to s u c h an e x t e n t t h a t the t r e a t m e n t of some e s p e c i a l l y i m p o r t a n t p o i n t s might become o b s c u r e d . T h u s oy o n l y m e n t i o n i n g the names of the more i m p o r t a n t a u t h o r s i n the f i e l d , an e x p e r i e n c e d g e n e t i c i s t c o u l d e a s i l y f i n d t h e n e c e s s a r y b i b l i o g r a p h i c a l r e f e r e n c e , w h i l e f o r o t h e r s the r e a d i n g of s p e c i a l i z e d p a p e r s m i g h t be r a t h e r c o n f u s i n g .
The q u e s t i o n of e x p l a i n i n g the d i v e r s i t y of l i v i n g o r g a n i s m s became i m p o r t a n t around the m i d d l e of t h e 1 8t n c e n t u r y , i n v i e w of the r a t h e r g r e a t number of t a x a w h i c h had b e e n a c c u m u l a t e d i n c o n s e q u e n c e of the e x p a n s i o n of w o r l d s h i p p i n g and t h e e x p l o r a t i o n of c o l o n i a l a r e a s by the g r e a t E u r o p e a n p o w e r s . S p e c i a l methods of an a r c h i v i s t i c n a t u r e were r e q u i r e d to b r i n g o r d e r i n t o i t and t h i s was the g r e a t m e r i t of LINNAEUS t o have p r o v i d e d an o r d e r l y a r r a n g e m e n t , e s t a b l i s h i n g b o t h f i r m c o n c e p t s s u c h as t h a t of the s p e c i e s and b a s i c n o m e n c l a t u r a l r u l e s f o r c l e a r i d e n t i f i c a t i o n . B o t h , t h e s p e c i e s c o n c e p t and t h e b a s i c n o m e n c l a t u r a l r u l e s t h e n e s t a b l i s h e d , a r e v a l i d s t i l l t o d a y . LINNAEUS r e c o g n i z e d t h a t h i s s y s t e m was an a r t i f i c i a l o n e , b u t he soon came t o t h e c o n c l u s i o n t h a t t h e r e e x i s t s an u n d e r l y i n g
N a t u r a l S y s t e m . The o r i g i n of the e x i s t i n g d i v e r s i t y d i d n o t r e p r e s e n t any d i f f i c u l t y to h i m , s i n c e he a c c e p t e d f i r m l y the b i b l i c a l i n t e r p r e t a t i o n and s i m p l y c o n c l u d e d : t h e r e a r e many s p e c i e s as had been
was e s p e c i a l l y i n t e r e s t e d i n the o b s e r v a t i o n s t h a t f o s s i l s p e c i e s were a l w a y s found o n l y i n a r e s t r i c t e d s e r i e s of g e o l o g i c a l s t r a t a and t h e n s u b s t i t u t e d f r e q u e n t l y by r a t h e r s i m i l a r s p e c i e s . T h i s e x t i n c t i o n and the
f o l l o w i n g new f o r m a t i o n of s p e c i e s he a l s o i n t e r p r e t e d as a c t s of t h e C r e a t o r , b u t he added some new e l e m e n t s . He f o r m u l a t e d the h y p o t h e s i s t h a t at d i f f e r e n t g e o l o g i c a l p e r i o d the C r e a t o r became d i s s a t i s f i e d w i t h h i s c r e a t i o n s , p r o v i d e d a d i l u v i u m d e s t r o y i n g a l l e l e m e n t s of f l o r a and f a u n a , r e s u m i n g t h e n , the p r o c e s s of c r e a t i o n . G e o l o g i s t s d i d not f i n d p r o o f t h a t s u c h g e n e r a l c a t a s t r o p h i c c h a n g e s had e v e r o c c u r e d . On the c o n t r a r y , they found t h a t some f o s s i l t a x a , s p e c i a l l y s p e c i e s , d i s a p e a r e d , i . e . , became e x t i n c t and t h e n were
s u b s t i t u t e d by new o n e s at some s p e c i f i c g e o l o g i c a l p e r i o d , w h i l e i n o t h e r s s u c h e v e n t s had t a k e n p l a c e at q u i t e d i f f e r e n t g e o l o g i c a l moments. F u r t h e r m o r e , s c i e n t i s t s may have come t o r e j e c t C U V I E R ' s h y p o t h e s i s as f u n d a m e n t a l l y i l l o g i c a l and t h u s as i n a c c e p t a b l e : i t a t t r i b u t e s to the Supreme C r e a t o r the human q u a l i t y of u s i n g t h e s i m p l e method of " t r i a l and e r r o r " r e p e a t e d l y . I n f a c t C U V I E R ' s h y p o t h e s i s was not a c c e p t e d as a v a l i d e x p l a n a t i o n , not o n l y b e c a u s e n o t h a v i n g been p r o v e d , but by l e a d i n g to too many c o n t r a d i c t i o n s . Thus an a l t e r n a t i v e e x p l a n a t i o n was r e q u i r e d .
The g e n e r a l s i t u a t i o n i n the s e c o n d h a l f of the 1 8t n and the f i r s t of the 1 9t n c e n t u r i e s may e a s i l y have c a u s e d d i s c u s s i o n s of a n o t h e r n a t u r e . I t was e v i d e n t t h a t the p o l i t i c a l s y s t e m of t h e a b s o l u t e monarchy had r e s u l t e d i n s o c i a l m i s e r y and e c o n o m i c b a n k r u p t c y , r e q u i r i n g d r a s t i c c h a n g e s . Some t h o u g h t the o n l y s o l u t i o n to c o n s i s t i n o n e , v e r y d r a s t i c and r e v o l u t i o n a r y c h a n g e , w h i l e o t h e r s p r e f e r r e d a s e q u e n c e of s m a l l e r c h a n g e s w i t h o u t a g e n e r a l u p h e a v a l , i . e . t h e p r o c e s s of s l o w , but c o n t i n u o u s e v o l u t i o n towards a p r e e s t a b l i s h e d e n d . The F r e n c h f o l l o w e d the f i r s t m e n t i o n e d way, t h a t of t h e g r e a t F r e n c h r e v o l u t i o n , w h i l e i n E n g l a n d and e l s e w h e r e t h e p r o c e s s of s l o w and g r a d u a l change was a d o p t e d . S i m i l a r t h o u g h t s may have
p l a y e d c o n s i d e r a b l e r o l e i n s c i e n t i f i c t h i n k i n g . C U V I E R ' s h y p o t h e s i s of r e p e a t e d d i l u v i a c o r r e s p o n d e n d r a t h e r t o t h a t of r e v o l u t i o n a r y c h a n g e , w h i l e A u g u s t e de S t . H i l a i r e , LAMARCK and o t h e r s a c c e p t e d an e v o l u t i o n a r y h y p o t h e s i s . They p o s t u l a t e d t h a t t a x a ( s p e c i e s ) were s t e p by s t e p t r a n s f o r m e d i n t o new o n e s . No p r o o f of t h i s i s a v a i l a b l e owing t o the f a c t t h a t s u c h e v o l u t i o n a r y t r a n s f o r m a t i o n s r e q u i r e e v i d e n t l y g e o l o g i c a l p e r i o d s , much l o n g e r t h a n l i f e of one s c i e n t i s t o r e v e n t h a t of s e v e r a l s u c c e s s i v e g e n e r a t i o n s of s c i e n t i s t s . But s e v e r a l s e r i e s of f o s s i l s have been found i n s u b s e q u e n t g e o l o g i c a l p e r i o d s , s h o w i n g s t a g e s i n the d e v e l o p m e n t of some c h a r a c t e r s w h i c h can be i n t e r p r e t e d as s u c c e s s i v e p h a s e s i n an e v o l u t i o n a r y c h a i n , f o r i n s t a n c e the f o r m a t i o n of the f o o t of h o r s e s , t h e t r u n k i n e l e p h a n t s or o t h e r s l i n k i n g apes to Homo sapiens. I n s u c h s e r i e s of f o s s i l s the s p e c i e s f o l l o w i n e a c h o t h e r a r e most p r o b a b l y n o t d i r e c t l y c o n n e c t e d , but r e p r e s e n t o n l y s t e p s i n a g e n e r a l p h y l o g e n e t i c s e q u e n c e . The s p e c i e s at one l e v e l need not to have been the a c t u a l a n c e s t o r of the f o s s i l s p e c i e s of the f o l l o w i n g l e v e l . S t u d i e s of c o m p a r a t i v e m o r p h o l o g y have a l s o r e s u l t e d i n e s t a b l i s h i n g what m i g h t be c o n s i d e r e d as s u c c e s s i v e s t e p s i n an e v o l u t i o n a r y s e q u e n c e even w i t h r e g a r d s to c h a r a c t e r s of h i g h e r t a x a . The s e q u e n c e f r o m P t e r i d o p h y t e s o v e r P t e r i d o s p e r m s and Gymnosperms to A n g i o s p e r m s shows an a l m o s t c o n t i n u o u s c h a n g e . From the s t i l l a u t o t r o p h i c h a p l o i d p r o t h a l l u m of f e r n s i t p a s s e s t o the f e m a l e gametophyte formed w i t h i n the f e m a l e t i s s u e of t h e d i p l o i d s p o - r o p h y t e . The male gametophyte may f o r m i n the G i n g k o a l e s a tube o r h a u s t o r i u m p r o d u c i n g s t i l l two m o b i l e s p e r m a t o c y t e s , u n t i l f i n a l l y i n t h e Gymnosperms s u c h h a u s t o r i u m , now c a l l e d p o l l e n t u b e , t r a n s p o r t s t h e two male n u c l e i to c o m p l e t e f e r t i l i z a t i o n of t h e o o s p h e r e . The d e c i s i v e e l e m e n t a l l o w i n g t h e e v o l u t i o n a r y c o n c e p t t o be g e n e r a l l y a c c e p t e d c o n s i s t s i n t h e c o m p l e t e a b s e n c e of any e v i d e n c e t o t h e c o n t r a r y . The e v o l u t i o n a r y c o n c e p t was c o n s e q u e n t l y s l o w l y a c c e p t e d , m a i n l y d u r i n g the f i r s t h a l f of l a s t c e n t u r y and i s s t i l l c o n s i d e r e d v a l i d up t o d a y .
As l o n g as the b i b l i c a l c o n c e p t had b e e n
a c c e p t a b l e , t h e r e was no p r o b l e m r e g a r d i n g t h e o r i g i n of l i f e and the d o g m a t i c s t a t e m e n t : "omne v i v u m ex v i v o " remained v a l i d . Some c o n c e p t s r e g a r d i n g t h e o r i g i n of l i v i n g o r g a n i s m s had b e e n f o r m u l a t e d and formed p a r t of a r i s t o t e l e a n p h i l o s o p h y , r e g a r d e d as f u n d a m e n t a l s i n c e the G r e e k c l a s s i c s . D u r i n g the l a s t c e n t u r y , PASTEUR and o t h e r s a c c u m u l a t e d e x p e r i m e n t a l e v i d e n c e d i s p r o v i n g the s p e c u l a t i o n t h a t l i f e c o u l d have o r i g i n a t e d by some c o m b i n a t i o n of dead m a t t e r , t h u s at l e a s t a p p a r e n t l y d i s p r o v i n g the o c c u r r e n c e of " s p o n t a n e o u s g e n e r a t i o n " . S u c h e x p e r i m e n t s , though w i t h o u t p o s i t i v e r e s u l t s , d i d not p r o v e a n y t h i n g , s i n c e i t was not shown t h a t the e x p e r i m e n t a l c o n d i t i o n s had been t h e r i g h t o n e s . On the o t h e r h a n d , i f the e v o l u t i o n a r y h y p o t h e s i s i s a c o r r e c t o n e , l i f e must have s t a r t e d somehow, somewhere and at some t i m e . R a t h e r r e c e n t l y s c i e n t i f i c r e s u l t s have i n d i c a t e d how and when l i f e c o u l d have had i t s o r i g i n . G e o l o g i c a l and p e t r o g r a p h i c e v i d e n c e i n d i c a t e t h a t i n the c o u r s e of some 5 b i l l i o n y e a r s the e a r t h s u f f e r e d
i m p o r t a n t c h a n g e s . I n about the f i r s t h a l f of t h i s l o n g p e r i o d , f r e e o x y g e n was e i t h e r a b s e n t o r e x t r e m e l y r a r e i n the atmosphere w h i c h c o n t a i n e d l a r g e r amounts of n i t r o g e n , c a r b o n d i o x i d e and ammonia v a p o r , w h i c h form under some c o n d i t i o n s , w a t e r s o l u b l e c o m p l e x m o l e c u l e s d i s s o l v e d i n o c e a n w a t e r s o r r i v e r s . S u c h c h e m i c a l c o m b i n a t i o n s s i m i l a r to p r o t e i n s have i n f a c t been p r o d u c e d e x p e r i m e n t a l l y . As soon h o w e v e r , as some
p h o t o c h e m i c a l l y a c t i v e c o m b i n a t i o n s s i m i l a r o r i d e n t i c a l to c h l o r o p h y l l were f o r m e d , the s i t u a t i o n changed and f r e e o x y g e n appeared i n the a t h m o s p h e r e . T h i s i n t u r n would have c a u s e d the immediate d e s t r u c t i o n t h r o u g h o x i d a t i o n of many or most " o r g a n i c compounds" - so c a l l e d by t r a d i t i o n , though not of o r g a n i c o r i g i n -u n l e s s t h e y were a l r e a d y p r o t e c t e d by s p e c i a l membranes. T h i s m i g h t be c o n s i d e r e d as a p o s s i b l e o r i g i n of l i v i n g o r g a n i s m s . A g a i n i t must be s t a t e d t h a t t h e r e i s no p r o o f of t h i s a s s u m p t i o n , b u t i t shows t h a t s u c h an o r i g i n might have t a k e n p l a c e .
So f a r I have t r i e d to summarize why the c o n t i n u o u s p r o c e s s of e v o l u t i o n h a s become g e n e r a l l y a c c e p t a b l e . I t was n e v e r p r o v e d , b u t t h e r e a r e no c o n t r a d i c t i n g f a c t s known and i t i s n o t o n l y l o g i c a l , b u t a l s o i n agreement w i t h a l l f a c t s known, i n n a t u r e or f r o m e x p e r i m e n t s . Now I w i l l p a s s to d i s c u s s the p r o b a b l e n a t u r e of t h e e v o l u t i o n a r y mechanism w h i c h a l l o w s the permanent c o n t i n u a t i o n of the e v o l u t i o n a r y p r o c e s s . The c o n c e p t of i t s n a t u r e w h i c h up to now w i d e l y was a c c e p t e d , c o u l d be r i g h t l y c a l l e d " d a r w i n i s m " and s h a l l be s u b m i t t e d t o a c r i t i c a l a n a l y s i s . However, b e f o r e e n t e r i n g i n t o t h i s s u b j e c t , LAMARCK's i d e a s about the r o l e of t h e s u p p o s e d i n h e r i t a n c e of a c q u i r e d c h a r a c t e r s must be m e n t i o n e d r a p i d l y , m a i n l y f o r h i s t o r i c a l r e a s o n s . LAMARCK, a F r e n c h b i o l o g i s t w i t h a v a s t t a x o n o m i c k n o w l e d g e b e l i e v e d t h a t some c h a r a c t e r i s t i c s i n a n i m a l s , i n c l u d i n g man, c o u l d n o t o n l y be improved by i n t e n s e t r a i n i n g , b u t a l s o become to be h e r i t a b l e i n t h i s
i m p r o v e d f o r m . H o w e v e r , even i n human s o c i e t y t h e r e are p r o b a b l y more c a s e s s h o w i n g the c o n t r a r y , i . e . , of
i n e f f i c i e n t c h i l d r e n of o u t s t a n d i n g p e o p l e n o t o n l y i n some s p e c i a l f i e l d s b u t a l s o a f t e r s p e c i a l t r a i n i n g . E x p e r i m e n t s were c a r r i e d out by s e v e r a l b i o l o g i s t s , and t h e y d i d n o t show any s i g n s of an e x i s t e n c e of
h e r i t a b i l i t y of a c q u i r e d c h a r a c t e r s . Thus LAMARCK1s h y p o t h e s i s was r e j e c t e d and f i n a l l y abandoned.
DARWIN's way of t h i n k i n g was p r o b a b l y p r e d i s p o s e d by the g e n e r a l s p i r i t i n E n g l a n d at t h e t i m e of t h e b e g i n n i n g of i n t e n s e i n d u s t r i a l i z a t i o n where b o t h e x t r e m e c o m p e t i t i o n between new i n d u s t r i a l i s t s and at t h e same t i m e v e r y s t r o n g e x p l o i t a t i o n of t h e l a b o u r f o r c e s were c o n s i d e r e d e s s e n t i a l f o r p r o g r e s s . F u r t h e r m o r e , he knew t h a t i n a n i m a l b r e e d i n g , s u d d e n h e r i t a b l e c h a n g e s of c h a r a c t e r i s t i c s d i d o c c u r , at t h a t t i m e c a l l e d " s p o r t s " , now m u t a t i o n s . F i n a l l y , t r a v e l l i n g as m e d i c a l o f f i c e r o v e r the A t l a n t i c Ocean
and l a n d i n g on t h e s h o r e of R i o de J a n e i r o , he became aware of the r i c h n e s s of b o t h f l o r a and f a u n a of t h e t r o p i c s , so much c o n t r a s t i n g w i t h the c o m p a r a b l y r a t h e r poor v e g e t a t i o n i n E n g l a n d . C o m b i n i n g a l l t h e s e
t h o u g h t s and o b s e r v a t i o n s , he c o n c l u d e d t h a t a l s o i n n a t u r e t h e r e must e x i s t an e x t r e m e s t r u g g l e f o r s u r v i v a l and t h a t any h e r e d i t a r y c h a n g e s w h i c h i n c r e a s e the
c h a n c e s f o r s u r v i v a l would be s e l e c t e d r a p i d l y t h r o u g h c o m p e t i t i o n w i t h t h e i r own p r e d e c e s s o r s . Thus the h y p o t h e s i s of d a r w i n i s t i c " N a t u r a l S e l e c t i o n " was e s t a b l i s h e d . DARWIN d e l a y e d p u b l i c a t i o n of h i s h y p o t h e s i s u n t i l much l a t e r a f t e r h a v i n g a c c u m u l a t e d a g r e a t number of o b s e r v a t i o n s w h i c h he c o u l d i n t e r p r e t w i t h h i s h y p o t h e s i s . T h i s was r a t h e r r a p i d l y a c c e p t e d by an i n c r e a s i n g number of s c i e n t i s t s and g a i n e d g e n e r a l a c c e p t a n c e as a s a t i s f a c t o r y e x p l a n a t i o n as a mechanism of the e v o l u t i o n a r y p r o c e s s , based e x c l u s i v e l y on m e c h a n i c a l e l e m e n t s and f r e e of any v i t a l i s t i c or b i b l i c a l c o n c e p t s . E v i d e n t l y , as was the c a s e r e g a r d i n g the h y p o t h e s i s of e v o l u t i o n as a p r o c e s s , no e x p e r i m e n t a l p r o o f c o u l d be f u r n i s h e d : e v o l u t i o n a r y p r o g r e s s i s s o s l o w , r e q u i r i n g g e o l o g i c a l time s c a l e s , b u t not some based on the d u r a t i o n of human l i f e . With the i n t e n t i o n , h o w e v e r , to p r o v i d e
" p r o o f " f o r the d a r w i n i a n h y p o t h e s i s , h i s f o l l o w e r s a c c u m u l a t e d a v e r y g r e a t volume of o b s e r v a t i o n s w h i c h were i n t e r p r e t e d a c c o r d i n g to the r e q u i r e m e n t s of the d a r w i n i a n t h e o r y . I n f a c t , the l a t t e r became a dogma: e i t h e r o b s e r v e d s t r u c t u r e s or f u n c t i o n s c o u l d be
i n t e r p r e t e d a c c o r d i n g to d a r w i n i s m o r t h e y were s i m p l y d i s r e g a r d e d . With t h i s form of p r o c e d u r e a tremendous b i a s was i n t r o d u c e d . Such b i a s h a s l e d to q u i t e e r r o n e o u s i n t e r p r e t a t i o n s of c h a r a c t e r s to be of v a l u e tor i n c r e a s i n g s u r v i v a l c a p a c i t y . An a l m o s t d o g m a t i c b e l i e f i n the e v e r p r e s e n c e of d a r w i n i a n n a t u r a l s e l e c t i o n has c a u s e d e v e n a t e l e o l o g i c a l f o r m of t h i n k i n g . E v e r y c h a r a c t e r of an o r g a n i s m has to s e r v e somehow f o r one p u r p o s e s p e c i a l l y : to improve s u r v i v a l c a p a c i t y . U n f o r t u n a t e l y t h i s p r i n c i p l e was n o t r a r e l y u s e d , i n t e r p r e t i n g o n l y the f u n c t i o n s of c h a r a c t e r s of l i v i n g o r g a n i s m w i t h o u t p r o v i n g t h a t s u c h an i n c r e a s e i n s u r v i v a l c a p a c i t y had been a c h i e v e d . One of many
e x a m p l e s o n l y s h a l l be m e n t i o n e d i n some d e t a i l . I n the h i g h e r p l a n t s ( A n g i o s p e r m s ) t h e f u n c t i o n of the f l o r a l o r g a n s c o n s i s t s i n a l l o w i n g p o l l i n a t i o n . The s t r u c t u r e of t h e f l o r a l o r g a n s h a s however a l s o b e e n used l a r g e l y r e e s t a b l i s h o r d e r i n a " N a t u r a l S y s t e m " , i . e . , one w h i c h c o r r e s p o n d s to t h e c h a n g e s w h i c h had o c c u r r e d c u r i n g e v o l u t i o n . C o n s e q u e n t l y , i n a p p l y i n g the d a r w i n i a n dogma, e a c h s p e c i a l f e a t u r e of f l o r a l o r g a n s must r e p r e s e n t some improvement i n t h e p o l l i n a t i n g p r o c e s s and t h r o u g h i t to an i n c r e a s e i n s u r v i v a l c a p a c i t y . Among t h e f a m i l i e s of A n g i o s p e r m s , t h e o r c h i d f a m i l y i s o f t e n c i t e d as s h o w i n g t h e most a s t o n i s h i n g " a d a p t a t i o n s " between f l o w e r and p o l l i n a t o r , sometimes to a group of i n s e c t s , sometimes to one s p e c i e o r even to one s e x of a s p e c i e o n l y . The o f t e n c o m p l i c a t e d f l o r a l s t r u c t u r e s i n o r c h i d s became a v e r y s p e c i a l and o f t e n c i t e d o b j e c t of d a r w i n i s t i c i n t e r p r e t a t i o n . F o r i n s t a n c e i t was o b s e r v e d t h a t t h e y a t t r a c t e d by t h e i r s c e n t , c o l o r a t i o n and f o r m the m a l e s of w i l d b e e s w h i c h , c o n f u s i n g t h e f l o w e r w i t h a female of t h e i r s p e c i e s , t r i e d to c o p u l a t e w i t h the f l o w e r and d u r i n g t h e s e movements t r a n s f e r r e d
t h e p o l l i n i a from the a n t h e r to t h e r e c e p t i v e s t i g m a of the same f l o w e r , a p r o c e d u r e c a l l e d " p s e u d o c o p u l a " . The b e h a v i o u r of t h e i n s e c t m a l e s was- c l e a r l y o b s e r v e d , but not t h a t f r u i t s e t t i n g f o l l o w e d a l w a y s a f t e r p s e u d o c o p u l a . O t h e r i n t e r p r e t a t i o n s i n f l o w e r e c o l o g y were r a t h e r a n t h r o p o m o r p h i c . F o r i n s t a n c e l o n g i t u d i n a l d a r k s t r i p e s on f l o r a l l e a f o r g a n s p o i n t i n g somewhere i n t o the f l o w e r were i n t e r p r e t e d as s e r v i n g as i n d i c a t i n g d i r e c t i o n as
i f the p o l l i n a t o r had l e a r n e d some t r a f f i c s i g n s , w h i l e i g n o r i n g t r a n s v e r s e s t r i p e s i n d i c a t i n g to human
i m p e d i m e n t s of movement. I t seems v e r y d o u b t f u l t h a t b u m b l e b e e s w i l l s e t t l e one on t o p of the o t h e r , but a d e s i g n on an O p h r y s - f l o w e r , a p p e a r i n g to the human eye as an image of s u c h an i n s e c t , has b e e n i n t e r p r e t e d as i n f o r m i n g t h e i n s e c t t h a t some s p e c i a l food or d r i n k m i g h t be o b t a i n e d , an i m p r e s s i o n a n a l o g o u s to t h a t of a human p e r s o n on the o u t s i d e board of a b a r or
r e s t a u r a n t . However most i m p o r t a n t i s the f a c t t h a t g e n e r a l l y no t e s t i s made t o p r o v e t h e e f f i c i e n c y of the
a d a p t a t i v e r e l a t i o n s between f l o w e r and p o l l i n a t o r . H a v i n g s t u d i e d t r o p i c a l o r c h i d s f o r s e v e r a l d e c a d e s , I u n d e r t o o k numerous c o l l e c t i n g t r i p s i n many p a r t s of t h e A m e r i c a n t r o p i c s . S i n c e o r c h i d s a r e l o n g l i v e d
p e r e n n i a l s , t h e y can be e a s i l y found and c o l l e c t e d . Most, i f not a l l , s p e c i e s of t h i s f a m i l y f l o w e r e a c h at a s p e c i f i c time of t h e y e a r . They were o f t e n found
w i t h o u t f l o w e r s , b u t when c u l t i v a t e d u n d e r n e a r n a t u r a l c o n d i t i o n s t h e y showed t h a t they p r o d u c e f l o w e r s n o r m a l l y each y e a r . S i n c e t h e o v a r y i s g e n e r a l l y i n a bud s t a g e at f l o w e r i n g t i m e , d e v e l o p i n g o n l y f u r t h e r a f t e r a s u c c e s s f u l l p o l l i n a t i o n , r e a c h i n g m a t u r i t y a f t e r c o n s i d e r a b l e t i m e , i . e . a f t e r s e v e r a l weeks or m o s t l y many m o n t h s , one m i g h t t h u s e x p e c t t h a t f r u i t s i n some s t a g e of d e v e l o p m e n t s h o u l d be found on the mother p l a n t on i t s n a t u r a l h a b i t a t at any time of the y e a r and i n a b u n d a n c e . On the o t h e r hand f r u i t s were o n l y v e r y
r a r e l y found on t h e n a t u r a l h a b i t a t . T h i s t h e n i n d i c a t e s v e r y c l e a r l y t h a t the a d a p t a t i o n s between o r c h i d f l o w e r and p o l l i n a t o r a r e v e r y i n e f f i c i e n t under n a t u r a l c o n d i t i o n s and t h u s do n o t i n any way i n c r e a s e s u r v i v a l c a p a c i t y . O n l y o c a s i o n a l l y a few s p e c i e s were found w i t h a l l t h e i r f l o w e r s d e v e l o p e d i n t o f r u i t s . A d e t a i l e d s t u d y of s u c h s p e c i e s u n d e r c u l t i v a t i o n and c o n s t a n t o b s e r v a t i o n showed t h a t they had s p e c i a l , o f t e n m i n o r s t r u c t u r a l c h a n g e s r e s p o n s i b l e f o r a u t o m a t i c
se 1 f p o 1 1 i n a t i o n b e s i d e s a l l c h a r a c t e r s t y p i c a l f o r e a c h s p e c i e s or g e n u s . L e a v i n g a s i d e the few e x c e p t i o n a l c a s e s of a u t o m a t i c s e l f i n g , the m a j o r i t y of o r c h i d s show the r e l a t i v e i n e f f i c i e n c y of the a d a p t a t i o n s between o r c h i d f l o w e r and p o l l i n a t o r w h i c h r a t h e r r e p r e s e n t a d i s a d v a n t a g e and not an i n c r e a s e of s u r v i v a l c a p a c i t y . S i n c e however o r c h i d s have e v o l v e d and s t i l l e x i s t , t h e r e must be some c h a r a c t e r s r e e s t a b l i s h i n g e f f i c i e n t s u r v i v a l c a p a c i t y and t h u s a c t i n g as what may be c a l l e d a
" c o m p e n s a t i n g a d a p t a t i o n " . O r c h i d f r u i t s when mature can c o n t a i n , v a r y i n g from t a x o n to t a x o n , f r o m s e v e r a l t e n s of t h o u s a n d s to some h u n d r e d s of thousand s e e d s . S i n c e i t would be s u f f i c i e n t f o r the p r e s e r v a t i o n of a s p e c i e t h a t one seed per p a r e n t p l a n t would g i v e a
mature s p e c i m e n , the r a t e of s u r v i v a l under n a t u r a l c o n d i t i o n s must be an e x c e e d i n g l y low one and a l a r g e number of p o t e n t i a l d e s c e n d a n t s a r e e l i m i n a t e d by some f o r m of random e l i m i n a t i o n , i n d e p e n d e n t from i t s
i n d i v i d u a l s u r v i v a l c a p a c i t y . T h i s s h o u l d not h • i n t e r p r e t e d as i n d i c a t i n g t h a t t h e r e i s no n a t u r a l s e l e c t i o n of t h e d a r w i n i a n s o r t , b u t t h a t t h i s i s o n l y p a r t of the whole s e l e c t i v e p r o c e s s and p r o b a b l y a r a t h e r m i n o r p a r t of i t when compared w i t h random s e l e c t i o n . T h i s c o n c l u s i o n w i l l l e a d f o r c i b l y to r e c o n s i d e r many i n t e r p r e t a t i o n s g i v e n t o t h e e v o l u t i o n of c h a r a c t e r s w h i c h f o r m e r l y have b e e n c o n s i d e r e d as the r e s u l t of d a r w i n i a n s e l e c t i o n . I t w i l l i n no way a f f e c t the g e n e r a l a c c e p t a n c e of t h e e v o l u t i o n a r y p r o c e s s as s u c h , b u t o n l y c o n c e p t s r e g a r d i n g the e v o l u t i o n a r y m e c h a n i s m . The s c i e n c e of g e n e t i c s w h i c h has r a p i d l y d e v e l o p e d d u r i n g t h i s c e n t u r y , had f u r n i s h e d many c o n t r i b u t i o n s to the u n d e r s t a n d i n g of t h e e v o l u t i o n a r y p r o c e s s and i t s m e c h a n i s m , and t h u s , a f t e r c h a n g i n g the e x c l u s i v e i f not d o g m a t i c b a s i c c o n c e p t s of d a r w i n i s m i t becomes n e c e s s a r y to e n t e r i n t o a d i s c u s s i o n of p e r t i n e n t c y t o g e n e t i c q u e s t i o n s .
When MENDEL d i s c o v e r e d the r u l e s of t r a n s m i s s i o n and p e r s i s t e n c e of h e r e d i t a r y b a s i c u n i t s , t h i s was at f i r s t r e j e c t e d , b u t CORRENS and o t h e r s r e e s t a b l i s h e d the m e n d e l i a n r u l e s . DE V R I E S f o r m u l a t e d h i s m u t a t i o n h y p o t h e s i s by e r r o n e o u s l y i n t e r p r e t i n g r e s u l t s , but the e x i s t e n c e of h e r e d i t a r y c h a n g e s was l a t e r g e n e r a l l y a c c e p t e d . JOHANNSEN e s t a b l i s h e d a c l e a r d i s t i n c t i o n b e t w e e n t h e c a r r i e r of t h e g e n e t i c i n f o r m a t i o n , c a r r i e d o u t f r o m mother t o d a u g h t e r c e l l s and f r o m g e n e r a t i o n to g e n e r a t i o n w h i c h he c a l l e d t h e " g e n " and on the o t h e r s i d e the a c t u a l m a n i f e s t a t i o n of t h i s i n f o r m a t i o n the " p h e n o t y p e " . The f a c t t h a t s p e r m a t o c y t e s or p o l l e n t u b e s t r a n s f e r o n l y and w i t h r e g u l a r i t y n u c l e i i n t o the o o c y t e r a r e l y a l s o some s m a l l p a r t of c y t o p l a s m , made i t e v i d e n t t h a t o n l y n u c l e i a r e r e s p o n s a b l e f o r g e n e t i c t r a n s m i s s i o n . C y t o l o g i s t s p r o v e d t h e n t h a t m a i n l y t h e chromosomes of
the v a r i o u s components of the n u c l e u s were r e s p o n s i b l e f o r t h a t t r a n s m i s s i o n t h r o u g h the c o m p l e x m e c h a n i c a l b a s i s of m e n d e l i a n s e g r e g a t i o n s . A l s o the chromosomes have a complex s t r u c t u r e . Sometimes l i v i n g c e l l s show t h a t chromosomes c o n t a i n a s p i r a l l y e n r o l l e d t h r e a d or t h r e a d s , the chromosomes, though i t was l o n g under d i s c u s s i o n whether t h e s e remained i n t a c t d u r i n g the r e s t i n g s t a g e s of the n u c l e u s . A f t e r t r e a t m e n t of l i v i n g chromosomes ( i . e . w i t h o u t f i x a t i o n of any s o r t ) , t h e s e s p i r a l s c o u l d become v i s i b l e w i t h o u t s t a i n i n g , but c o n s i d e r i n g t h e i r t h i c k n e s s they l e a v e a c e n t r a l s p a c e w h i c h must be f i l l e d by some m a t e r i a l , the " m a t r i x "
f o r m i n g the main body of each chromosome. I n t r e a t i n g l i v i n g c e l l s d u r i n g n u c l e a r d i v i s i o n by v a r i o u s
c h e m i c a l s (ammonia, n i t r a t e s of C a , Na, L i , e t c ) I o b s e r v e d (.BRTEGKR u n p u b l i s h e d ) t h a t the chromosomes s t a r t
to s w e l l , chromonemas b e c o m i n g v i s i b l e w i t h i n a c o l o r l e s s and u n i f o r m m a t r i x w h i c h t h u s d i f f e r s c l e a r l y from the s u r r o u n d i n g g r a n u l a r c y t o p l a s m . The swe11ing•mat r i c e s touch and f u s e f i n a l l y w h i l e the chromonema u n r o l l a l m o s t c o m p l e t e l y . Thus the f i n a l a s p e c t d i f f e r s o n l y i n so f a r from a n u c l e u s i n the r e s t i n g s t a g e t h a t i t has no o u t e r membrane nor a d e f i n i t e f o r m . The f u n c t i o n s of the m a t r i x are unknown, but i t c e r t a i n l y lias no p a r t i n p r e s e r v i n g a g e n e t i c i n f o r m a t i o n .
The chromonemas a r e r a t h e r l o n g and t h i n t h r e a d s , though of v a r y i n g t h i c k n e s s n o d u l e s of v a r y i n g s i z e s b e i n g c o n n e c t e d by a t h i n t h r e a d . The p e c u l a r i t y of both m i t o s i s and m e i o s i s a l s o i n d i c a t e c l e a r l y t h a t t h e r e e x i s t some o r d e r l y s e q u e n c e i n the arrangement of gen l o c i , l i n k e d w i t h each o t h e r f i x e d r a t e s when
l o c a t e d i n the same chromonema. A t t e m p t s were made to d e t e r m i n e the s i z e of a gen l o c u s . The t o t a l l e n g t h of the chromonema can be measured w i t h some a c c u r a c y . The t o t a l number of gen l o c i has been e s t i m a t e d f o r some s p e c i e s to be of the o r d e r of s e v e r a l t h o u s a n d s .
A chromonema i s composed of two c h e m i c a l l y d i f f e r e n t p a r t s : t h e D N A - c h a i n , formed by l o n g i t u d i n a l u n i o n s of o n l y f o u r k i n d of n u c l e o t i d e s and i t s p r o t e i n c o v e r . S i n c e t h e DNA c h a i n was d i s c o v e r e d i t was
p o s t u l a t e d t h a t i t s p a r t s s h o u l d c o n t a i n p e r m a n e n t l y the g e n e t i c m e s s a g e s i n some coded form w h i c h t h e n s ? i l l be a c t i v a t e d and t r a n s m i t t e d somehow and somewhere to be e x e c u t e d and t r a n s f o r m e d i n t o p h e n o t y p i c m a n i f e s t a t i o n s . I t was assumed f u r t h e r t h a t t h e f o u r n i t r o g e n b a s i s i n v a r i o u s numbers of a l l c o m b i n a t i o n s and p e r m u t a t i o n s would f u r n i s h the b a s i s f o r the t r a n s m i s s i o n of g e n e t i c i n f o r m a t i o n s of the numerous gen l o c i and the a l l e l s of a s p e c i e . However s i n c e the same n u c l e o t i d e s are
p r e s e n t i n a l l s p e c i e s , i t seems to me v e r y d o u b t f u l i f t h e y would be s u f f i c i e n t to b u i l d up so many d i f f e r e n t t y p e s of g e n e t i c m e s s a g e s . B e f o r e the d i s c o v e r y of the D N A - c h a i n , i t was a c c e p t e d t h a t p r o t e i n s were t h e b a s i s of what was f i r s t c a l l e d a
" m e n d e l i a n f a c t o r " and l a t e r a g e n . I t would seem to me more l o g i c a l t o r e t u r n to s u c h an i n t e r p r e t a t i o n ,
c o n s i d e r i n g t h a t p r o t e i n s would be a more adequate c h o i c e i n v i e w of t h e i r c h e m i c a l c o m p l e x i t y and d i v e r s i t y as t h e m a t e r i a l b a s i s of a gen l o c u s and i t s v a r i o u s a l l e l s . The D N A - c t j a i n would t h e n have the f u n c t i o n to be the f i r s t s t e p i n a s e q u e n c e t r a n s f e r r i n g the i n f o r m a t i o n to o t h e r p a r t s of t h e c e l l or o t h e r c e l l s a b l e to p r o d u c e p h e n o t y p i c m a n i f e s t a t i o n s . I t r e a l l y does not m a t t e r v e r y much w h e t h e r we a c c e p t the f o r m e r a s s u m p t i o n of the D N A - c h a i n o r t h a t of i t s p r o t e i n c o o p e r as r e p r e s e n t i n g
t h e c o n s e r v e r of t h e coded g e n e t i c i n f o r m a t i o n .
The c o n s e r v a t i o n of t h e whole g e n o t y p i c i n f o r m a t i o n i n some p a r t s of t h e chromonemas seems to be the l a s t c o n c l u s i o n w h i c h c a n be a p p l i e d i n a g e n e r a l way to a l l o r g a n i s m s w i t h normal m i t o s i s and m e i o s i s . R e g a r d i n g i f c o n n e c t i o n w i t h t h e f i n a l p h e n o t y p i c m a n i f e s t a t i o n s , t h e r e a r e some i n d i c a t i o n s r e f e r i n g to s p e c i a l c a s e s , b u t w h i c h r e p r e s e n t and at p r e s e n t m e r e l y some f o r m of p i e c e s of a p r e l i m i n a r y w o r k i n g h y p o t h e s i s to be f u r t h e r t e s t e d . I t must be remembered t h a t the g e n o t y p e as a
whole r e p r e s e n t s a k i n d of m a s t e r - p l a n w h i c h n o t o n l y d e t e r m i n e s the d i f f e r e n t p h a s e s of o n t o g e n e t i c
d e v e l o p m e n t , b u t a l s o t h e f u n c t i o n i n g i n t h e a d u l t . Though i n some c a s e s p h e n o t y p i c m a n i f e s t a t i o n s seem to be c o n t r o l e d by one or few gens o n l y , i n f a c t a number of m o d i f i e r gens a r e a l s o i n v o l v e d and i n a d d i t i o n the m a n i f e s t a t i o n d e p e n d s on f r o m i n f l u e n c e s from t h e o u t s i d e . We do not y e t know a n y t h i n g about when and how the
g e n e t i c message i s m o d i f i e d under the i n f l u e n c e of e x t e r n a l f a c t o r s . I t i s e q u a l l y unknown how c e r t a i n p a r t s of the g e n e t i c message a r e a c t i v a t e d i n some c e l l s i n time and s p a c e w i t h i n an o r g a n i s m , though the whole message i s p r e s e n t i n chromosomes of a l l c e l l s of t h a t o r g a n i s m . Some a u t h o r s have a t t r i b u t e d a c t i v a t i o n to p r o t e i n m o l e c u l e s of the D N A - c o v e r , w h i l e o t h e r s admit t h a t hormones might be r e s p o n s i b l e . But what m i g h t a c t i v a t e t h e s e " a c t i v a t e r s " at the r i g h t time and p l a c e o n l y i n some b u t not a l l c e l l s ? I t i s assumed t h a t m e s s e n g e r - R N A , d i f f u s i n g from the chromonema i n t o the
c e l l t r a n s p o r t s somehow the message to o t h e r p a r t s of the c e l l s u c h as the r i b o s o m e w h i c h t h e n a r e a b l e to decode the message and p r o v i d e s i t s p h e n o t y p i c
r e a l i z a t i o n . But when no s u c h s p e c i a l i n c l u s i o n s a r o known to e x i s t , what p a r t does t h e d e c o d i n g ? How ou.i an i n d i v i d u a l c e l l ''know" what s i z e , shape or
f u n c t i o n i t has to assume? SPERMANN, HARRISON and t h e i r g r o u p s have e s t a b l i s h e d t h a t a c e r t a i n g r o u p of
u n d i f f e r e n t i a t e d c e l l s i n embryos of A m p h i b i a n s i n d u c e c e l l s more on the o u t s i d e t o form normal e y e s or l e g s anywhere i n the e m b r y o , i n p l a c e s to w h i c h t h e y have been t r a n s p l a n t e d e x p e r i m e n t a l l y . How t h e y a c t i v a t e i n the i n d u c e d c e l l s the r e s p e c t i v e gen l o c i i s c o m p l e t e l y unknown. I n the p r o c e s s of r e g e n e r a t i o n of l o s t p a r t s or the r e c o v e r y of c u t t i n g s i n p l a n t s , somehow the c o u r s e of o n t o g e n e t i c d e v e l o p m e n t or o n l y p a r t s of i t a r e r e i n i t i a t e d i n a c c o r d a n c e to the g e n o t y p i c m a s t e r - p l a n . A g a i n i t i s n o t known what d e t e r m i n e s w h i c h p a r t i s r e i n i t i a t e d . E v i d e n t l y b i o l o g i s t s have not y e t d i s c o v e r e d e f f i c i e n t methods of e x p e r i m e n t a t i o n and o b s e r v a t i o n t o e n a b l e them to u n c o v e r t h e pathway or
p o s s i b l y t h e pathways l i n k i n g the c o n s e r v e d g e n o t y p i c m a s t e r - p l a n w i t h the p h e n o t y p i c m a n i f e s t a t i o n s . I t seems now i n d i c a t e d t o r e v i e w some o t h e r i t e m s w h i c h have been
i n c o r p o r a t e d i n t o t h e c u r r e n t e v o l u t i o n a r y t h e o r y .
Up t o t h e p o i n t of c o n s i d e r i n g the chrun .«orne as t h e c a r r i e r of g e n e t i c m e s s a g e s , s c i e n c e i s s t i l l on a f i r m b a s i s , but l i n k i n g the. g e n e t i c message to i t s p h e n o t y p i c m a n i f e s t a t i o n we have at p r e s e n t o n l y i n c o m p l e t e and r a t h e r vague w o r k i n g h y p o t h e s i s .
When T . H . MORGAN s t a r t e d h i s work i n g e n e t i c s he u s e d as l a b o r a t o r y a n i m a l the f r u i t f l y , p r e v i o u s l y found by CASTLE t o be e a s i l y c u l t i v a t e d and s t u d i e d i n m i l k b o t t l e s . B R I D G E S , t h e n o n l y a l a b o r a t o r y s e r v a n t ,
t h o u g h l a t e r a v e r y d i s t i n g u i s h e d g e n e t i c i s t , was t o l d to c o l l e c t f r u i t f l i e s i n o r c h a r d s , f r u i t s h o p s and e l s e w h e r e , t o c u l t i v a t e them and s e e what v a r i a t i o n s he c o u l d f i n d d i f f e r i n g from the common o r " w i l d t y p e " . He c a r r i e d t h i s work v e r y e f f i c i e n t l y o u t , i s o l a t i n g i n d i v i d u a l s w i t h a b e r r a n t c h a r a c t e r s , t e s t e d them i n c r o s s e s and k e p t o n l y t h o s e w h i c h gave c l e a r m e n d e l i a n o r n e a r - m e n d e l i a n s e g r e g a t i o n s i n s u c h t e s t c r o s s e s . A l l o t h e r a b e r r a n t f o r m s were s i m p l y d i s c a r d e d . T h i s method seemed t o a l l o w t o r e a c h g e n e r a l c o n c l u s i o n s r e g a r d i n g t h e n a t u r e of h e r e d i t y , b u t i n v o l v e d a v e r y s t r o n g b i a s r e g a r d i n g t h e g e n e r a l n a t u r e of m u t a t i o n s : namely t h a t t h e y were g e n e r a l l y r e c e s s i v e and r e d u c e d s u r v i v a l c a p a c i t y . G e n e t i c r e s e a r c h w i t h m i c e , r a t s , r a b b i t s * p o u l t r y o r w i t h m a i z e , p e a s , sweet p e a s , s n a p - d r a g o n , e t c . , c o n f i r m e d t h a t i n i t i a l l y mutant g e n e s were g e n e r a l l y r e c e s s i v e , b u t n o t a l w a y s s u b v i a b l e . N I L S O N - E H L E and C A S T , s t u d y i n g t h e h e r e d i t y of q u a n t i t a t i v e d i f f e r e n c e s , c o n c l u d e d on the o t h e r hand t h a t s u c h d i f f e r e n c e s were c o n t r o l l e d by r a t h e r numerous gen l o c i t h e a l l e l s of e a c h l o c u s when h e t e r o z y g o u s b e i n g i n t e r m e d i a t e between t h e h o m o z y g o t e s i n t h e i r p h e n o t y p i c m a n i f e s t a t i o n and had no e f f e c t on s u r v i v a l q u a l i t y i n any c o m b i n a t i o n . The a n a l y s i s of the m e n d e l i a n
p r o p o r t i o n s of m o n o f a c t o r i a l s e g r e g a t i o n s of t h i s n a t u r e i s m o s t l y d i f f i c u l t s i n c e the d i s t i n c t i o n of t h e t h r e e m o n o f a c t o r i a l g e n o t y p e s a r e not v e r y s h a r p owing t o g r a d u a t i o n s of t h e i r p h e n o t y p i c e x p r e s s i o n .
O t h e r c a s e s must be c o n s i d e r e d where the p h e n o t y p i c m a n i f e s t a t i o n of the h e t e r o z y g o t e s go beyond the range of v a r i a t i o n of e i t h e r h o m o z y g o t e , t h e o r i g i n a l one and the mutated o n e . A h e t e r o t i c m o n o f a c t o r i a l
e f f e c t has been s t u d i e d i n two c a s e s , t h e c o l o u r of the f e a t h e r s i n p o u l t r y and the f l o w e r c o l o u r i n some
c u l t i v a t e d form of Silene armaria. T h e s e c a s e s have been i n t e r p r e t e d a t t r i b u t i n g the p h e n o t y p i c e f f e c t to two e x t r e m e l y c l o s e l y l i n k e d gens i n the m u t a n t , one a r e c e s s i v e i n h i b i t o r and the o t h e r a dominant i n t e n s i f i e r w h i c h however i s h y p o s t a t i c w i t h r e g a r d s to the i n h i b i t o r when h o m o z y g o u s . The r e c e s s i v e i n h i b i t o r b e i n g i n a c t i v e i n h e t e r o z y g o t e s , the dominant i n t e n s i f i e r m a n i f e s t s i t s p h e n o t y p i c e f f e c t p l a i n l y . I n the c a s e of Llilcna w h i c h I used d u r i n g many y e a r s i n c l a s s w o r k f o r s t u d e n t s , many t h o u s a n d s of F2 p l a n t s were a n a l y z e d w i t h o u t any c a s e of a l i n k a g e b r e a k w h i c h m i g h t have p r o v e n the b a s i c
h y p o t h e s i s . I n m a i z e o r man as i n s e v e r a l o t h e r s p e c i e s h e t e r o s i s i s caused t h r o u g h h e t e r o t i c i n t e r a c t i o n of many gen l o c i . The u s e of h y b r i d s w i t h a maximum of s t r o n g l y h e t e r o t i c p a i r s of a l l e l s , r e s u l t e d w i t h i n b r e e d i n g
t h r o u g h autogamy or b r o t h e r - s i s t e r m a t i n g s i n a d e s a s t r o u s l o s s of v i g o u r caused by the a p p e a r a n c e of h o m o z y g o s i t y even o n l y i n some gen l o c i .
As l a s t c a s e the p o s s i b i l i t y s h a l l be mentionned of a mutant h a v i n g a dominant e f f e c t . I t seems t h a t i n s u c h c a s e s the mutant r e d u c e s s u r v i v a l c a p a c i t y
c o n s i d e r a b l y . S u c h c a s e s have b e e n r a r e l y o b s e r v e d and s t u d i e d , f o r i n s t a n c e by R . A . F I S H E R i n p o u l t r y .
A p p a r e n t l y the e x t r e m e l y s t r o n g p h e n o t y p i c a l e f f e c t of a dominant mutant c a u s e s a g e n e r a l i z e d u n b a l a n c e i n the g e n o t y p e .
From t h e f o r e g o i n g c o n s i d e r a t i o n s one must c o n c l u d e t h a t t h e r e e x i s t s no g e n e r a l r u l e f o r mutant a l l e l s to be a l w a y s f o r e v e n m o s t l y r e c e s s i v e and to r e d u c e g e n e r a l l y s u r v i v a l c a p a c i t y . I t s h o u l d a l s o be remembered t h a t no gen l o c u s w i l l c a u s e s p e c i f i c p h e n o t y p i c m a n i f e s t a t i o n s w h i c h a r e n o t a f f e c t e d by the p r e s e n c e of a l l e l s of o t h e r gen l o c i . T h e s e may a c t s i m p l y as m o d i f i e r o n l y , i . e . t h e i r p h e n o t y p i c m a n i f e s t a t i o n c o n s i s t s e x c l u s i v e l y i n m o d i f y i n g t h e e f f e c t s of a l l e l s of o t h e r gen l o c i and w h i c h c a n e a s i l y r e e s t a b l i s h l o s t s u r v i v a l c a p a c i t y . G e n e t i c i s t s and b r e e d e r s have used t h e s e p o s s i b i l i t i e s by c h a n g i n g t h e m o d i f i e r e f f e c t s by c a r e f u l l y p l a n n i n g a r t i f i c i a l s e l e c t i o n .
The t e r m " w i l d t y p e a l l e l " was u s e d t o i d e n t i f y a l l e l s p r e s e n t w i t h v e r y h i g h f r e q u e n c y i n n a t u r a l
p o p u l a t i o n or sometimes i n o l d and w e l l e s t a b l i s h e d r a c e s of c u l t i v a t e d p l a n t s . I t must however be remembered t h a t t h e " w i l d t y p e a l l e l s " must i n t u r n have appeared at some t i m e d u r i n g e v o l u t i o n o r b r e e d i n g and r e p r e s e n t e d o n c e m u t a t i o n s . T h u s the q u e s t i o n a r i s e s how a m u t a t i o n w i t h i t s i n i t i a l e x t r e m e l y low f r e q u e n c y might become as
f r e q u e n t as p r e s e n t day " w i l d t y p e g e n s " . I n t h e p r e c e d i n g p a r a g r a p h s c r i t i c i s m s a r e b r o u g h t f o r w a r d a g a i n a c e r t a i n monopoly a t t r i b u t e d to the p u r e l y d a r w i n i a n c o n c e p t as e x p l a i n i n g the e v o l u t i o n a r y p r o c e s s . T h u s i t becomes n e c e s s a r y to r e c o n s i d e r i n some d e t a i l the f a c t o r s w h i c h a r e i n v o l v e d d u r i n g t h i s p r o c e s s . I t s b a s i s c o n s i s t s e v i d e n t l y i n t h e s u b s t i t u t i o n of the
a l l e l s p r e s e n t at a g i v e n gen l o c u s by a new mutant a l l e l w h i c h c a u s e s a new way of p h e n o t y p i c m a n i f e s t a t i o n . T h i s m a n i f e s t a t i o n i s a l w a y s q u i t e u n p r e d i c t a b l e and one can e x p e c t t h a t i n i t i a l l y i t c a u s e s i n the g e n o t y p e as a w h o l e a c e r t a i n u n b a l a n c e . I t s f r e q u e n c y i s n e c e s s a r e l y at f i r s t e x t r e m e l y l o w , b u t t h e n i n c r e a s e s s u c c e s s i v e l y d u r i n g many g e n e r a t i o n s , s u b s t i t u t i n g t h e o r i g i n a l a l l e l and p o s s i b l y e l i m i n a t i n g i t c o m p l e t e l y . When a n a l y s i n g t h i s change i n o r g a n i s m s l i v i n g t o d a y , i t h a s become the c u s t o m t o d e s i g n a t e the a l l e l s p r e s e n t as " w i l d t y p e
a l l e l s " i n c o n t r a s t t o t h e i n f r e q u e n t new mutant a l l e l s . The p r e s e n t " w i l d t y p e a l l e l " on i t s p a r t must have o r i g i n a t e d at some p r e v i o u s t i m e as a mutant and has s u b s t i t u t e d the p r e c e d i n g o r i g i n a l a l l e l . T h i s p a r t of the e v o l u t i o n a r y p r o c e s s , the s u b s t i t u t i o n of p r e c e d i n g a l l e l s i s however s o s l o w t h a t i t c a n n o t be o b s e r v e d by d i r e c t o b s e r v a t i o n . But s u c h c h a n g e s have been c a u s e d
t h r o u g h a r t i f i c i a l s e l e c t i o n c a r r i e d out by g e n e t i c i s t s and b r e e d e r s . An a n a l o g o u s r e s u l t was e v i d e n t l y r e a c h e d by n a t u r a l s e l e c t i o n w h i c h c o n s i s t e d b o t h i n random and i n d a r w i n i a n s e l e c t i o n as e x p l a i n e d a l r e a d y a b o v e , the f i r s t a c o n s e q u e n c e of the h i g h l y e x c e s s i v e o f f s p r i n g of each p l a n t , w e l l beyond t h e minimum n e c e s s a r y to
s u b s t i t u t e i t s p r o g e n i t o r s and the s e c o n d a r e s u l t of d i f f e r e n c e s i n s u r v i v a l c a p a c i t y . I n o r d e r t o v i s u a l i z e how the e v o l u t i o n a r y p r o c e s s might have p r o g r e s s e d , i t became n e c e s s a r y to work out m a t h e m a t i c a l m o d e l s of p o p u l a t i o n g e n e t i c s , e s t a b l i s h i n g c e r t a i n i n d i s p e n s a b l e p r e m i s s e s w h i c h s h a l l now b r i e f l y be d i s c u s s e d .
M u t a t i o n P r e s s u r e
The m u t a t i o n r a t e i s g e n e r a l l y v e r y low and i f we a c c e p t a v a l u e of u = 0 , 0 0 1 as an upper maximum t h i s would e v i d e n t l y r e p r e s e n t an u n u s u a l l y h i g h o n e . I t would appear at f i r s t i n the h e t e r o z y g o u s s t a t e and the f o r m a t i o n of a homozygote might depend on t h e o c c u r e n c e of a second mutant a l l e l f o r w h i c h the e x p e c t e d f r e q u e n c y would be s t i l l s m a l l e r , b e i n g e q u a l to u^ = 1 ^ w i t h i n
the same progeny and w i t h o u t i n t e r c r o s s i n g . I f we assume however t h a t s u c h a m u t a t i o n would o c c u r i n n i n d i v i d u a l s w i t h homozygotes b e i n g formed t h r o u g h i n t e r c r o s s i n g , the t o t a l f r e q u e n c y of t h e mutant m i g h t r i s e a p p r e c i a b l y though h a r d l y r e a c h i n g a v a l u e of more t h a n 1%. E v e n t h i s v e r y s l o w i n c r e a s e m i g h t be c o n s i d e r e d s u f f i c i e n t s i n c e we d i s c u s s e v e n t s i n g e o l o g i c a l t i m e w h i c h a r e g e n e r a l l y c o u n t e d i n m i l l i o n s of y e a r s .
Number and I n t e r a c t i o n of A l l e l s P e r Gen L o c u s
Next we must c o n s i d e r t h e number of a l l e l s p e r gen l o c u s . E x p e r i m e n t a l e v i d e n c e i n d i c a t e s t h a t most f r e q u e n t l y t h e r e a r e o n l y two forms of phe.nof;y t) i c
m a n i f e s t a t i o n s p e r gen l o c u s . T h i s may e i t h e r mean t h a t o n l y two t y p e s of m u t a t i o n s were p o s s i b l e , e a c h
d e t e r m i n i n g one of two p h e n o t y p e s , or t h a t t h e r e m i g h t e x i s t any number of mutant a l l e l s but o n l y two forms of m a n i f e s t a t i o n s .
I n a c c o r d a n c e w i t h the n a t u r e of i n t e r a l l e l i n t e r a c t i o n t h e r e may e x i s t t h r e e g e n o t y p e s w i t h the m e n d e l i a n p r o p o r t i o n s of ( 1 : 2 : 1 ) o r two w i t h the p r o p o r t i o n ( 3 : 1 ) . T h i s means t h a t t h e number of p h e n o t y p e s would be r e d u c e d t o two, one of w h i c h w i t h t h r e e t i m e s the f r e q u e n c y of t h e o t h e r .
N o n - a l l e l i c I n t e r a c t i o n s
I f t h e a l l e l s at e a c h gen l o c u s s h o u l d not
i n t e r a c t w i t h e a c h o t h e r , the maximum of p h e n o t y p i c t y p e s w i t h n gen l o c i would be e i t h e r 3r o r 2r. T h i s number would be f u r t h e r r e d u c e d i n t h o s e c a s e s where a l l e l s of d i f f e r e n t l o c i s h o u l d i n t e r a c t i n s u c h a way t h a t v a r i o u s g e n o t y p e s would m a n i f e s t i d e n t i c a l p h e n o t y p e s . As an example c a s e s of s u c h i n t e r a c t i o n s w i l l be mentioned s t a r t i n g from a b i f a c t o r i a l p r o p o r t i o n of ( 9 + 3 + 3 + 1 ) . I n c a s e of a c u m u l a t i v e e f f e c t of the number of dominant a l l e l s , t h e p r o p o r t i o n might be changed t o ( 9 + 6 + 1 ) . I n c a s e of c o m p l e m e n t a r y i n t e r a c t i o n r e q u i r i n g at l e a s t one dominant a l l e l i n e a c h of t h e two l o c i , t h e r e s u l t would be a s e g r e g a t i o n of ( 9 + 7 ) o r when b o t h l o c i have
to be homozygous r e c e s s i v e ( 1 5 + 1 ) . The 9 p o s s i b l e g e n o t y p e s of a b i f a c t o r i a l s e g r e g a t i o n w i t h dominant a l l e l s i n b o t h l o c i would be r e d u c e d t o 4 p h e n o t y p e s and t h e n f u r t h e r t o a minimum of 2 p h e n o t y p e s by i n t e r a l l e l
i n t e r a c t i o n s . C o n s i d e r i n g the g e n e r a l l y v e r y h i g h t o t a l number of gen l o c c i , s u c h r e d u c t i o n s would s t i l l p r e s e r v e a g r e a t d e a l of d i v e r s i t y i n p o p u l a t i o n s of a s p e c i e , but p h e n o t y p e s based on s e v e r a l g e n o t y p e s would have a
f r e q u e n c y equal to the sum t o t a l of the i n d i v i d u a l g e n o t y p e s i n c l u d i n g h e t e r o z y g o t e s and t h u s be
c o n s i d e r a b l y l a r g e r t h a n t h a t of any g e n o t y p e i n d i v i d u a l l y .
Random S e l e c t i o n
Random s e l e c t i o n i s an a u t o m a t i c c o n s e q u e n c e (a) of the f a c t t h a t on t h e a v e r a g e e a c h i n d i v i d u a l of a p o p u l a t i o n p r o d u c e s more o f f s p r i n g than would be n e c e s s a r y to m a i n t a i n p o p u l a t i o n s i z e ; ( b ) of the e x i s t a n c e w i t h i n a p o p u l a t i o n of numerous p h e n o t y p e s w i t h d i f f e r e n t f r e q u e n c i e s and ( c ) i n c o n s e q u e n c e of d i f f e r e n c e s i n s u r v i v a l c a p a c i t y . I n the l a t t e r c a s e the f o l l o w i n g s h o u l d be e x p l a i n e d : i f a mutant a l l e l c a u s e s a r a t h e r weak m a n i f e s t a t i o n and t h i s o n l y when homozygous then i t may c a u s e a c e r t a i n u n b a l a n c e of the g e n o t y p e r e s u l t i n g i n lower s u r v i v a l c a p a c i t y . I f the p e n e t r a n c e s h o u l d be c o n s i d e r a b l e , the mutant a l l e l may m a n i f e s t i t s p h e n o t y p i c e f f e c t a l r e a d y i n the h e t e r o z y g o t e and t h u s a c t as a dominant a l l e l . I n t h i s c a s e t h e
u n b a l a n c e of the g e n o t y p e w i l l a l s o be much s t r o n g e r . I n f a c t r a t h e r few s u c h dominant m u t a n t s have been o b s e r v e d i n e x p e r i m e n t a l w o r k . F i n a l l y i f a mutant has v e r y l i t t l e p e n e t r a n c e , i t can be c o n s i d e r e d as a n e u t r a l a l l e l and w i l l h a r d l y a f f e c t s u r v i v a l c a p a c i t y . G e n e r a l l y the a c t i o n of i n d i v i d u a l m u t a n t s of t h i s type cannot be a n a l y z e d i n d i v i d u a l l y and t h e y a r e t h u s m a i n l y c o n s i d e r e d as m o d i f i e r s of t h e a c t i o n of o t h e r mutants w i t h a s t r o n g e r p e n e t r a n c e . I n f a c t s e l e c t i o n of s u c h m o d i f i e r s may a f f e c t and r e f o r c e the p e n e t r a n c e of o t h e r mutant a l l e l s , and remove s u b v i a b i 1 i t y . T h i s l a s t s t e p w i l l however n o t be anymore t h e r e s u l t of random s e l e c t i o n w h i c h , by d e f i n i t i o n , i s w i t h o u t d i r e c t i o n , d e p e n d i n g e x c l u s i v e l y on the f r e q u e n c i e s of p h e n o t y p i c
m a n i f e s t a t i o n s of m u t a n t s . I t may r e s u l t i n the
p r e s e r v a t i o n of some of them w i t h i n t h e p o p u l a t i o n and t h e a c c i d e n t a l e l i m i n a t i o n of o t h e r s i n t h e n e x t f o l l o w i n g g e n e r a t i o n . D i v e r s i t y i n t h e p o p u l a t i o n w i l l be r e d u c e d and h o m o g e n e i t y a c c o r d i n g l y i n c r e a s e d . E c o s e l e c t i o n i s a term w h i c h I p r o p o s e e x c l u s i v e l y t o i n d i c a t e s e l e c t i o n c a u s e d by i n t e r a c t i o n between p h e n o t y p e s , r e s p . t h e i r g e n o t y p e s p r e s e n t i n a
p o p u l a t i o n , and the e c o l o g i c a l c o n d i t i o n s under w h i c h the p o p u l a t i o n l i v e s . One can d i s t i n g u i s h t h r e e d i f f e r e n t s i t u a t i o n s : a) Some p h e n o t y p e s may n e i t h e r be a d v a n t a g e o u s n o r d i s v a n t a g e o u s u n d e r t h e e x i s t i n g c o n d i t i o n s and t h u s may be c o n s i d e r e d " n e u t r a l " , n o t s u f f e r i n g d a r w i n i a n s e l e c t i o n , e x c e p t at most i n t h e form of a m o d i f i e r s h i f t , s t a b i l i z i n g t h e p h e n o t y p e s and c o m p e n s a t i n g any e v e n t u a l l y e x i s t i n g s u b v i a b i l i t y . S i n c e s u c h
m a n i f e s t a t i o n s must have r e s u l t e d under random s e l e c t i o n r e f e r e n c e t o them was a l r e a d y made i n t h e p r e c e d i n g
p a r a g r a p h . Thus t h e y do not form any type of a d a p t a t i o n .
b ) O t h e r p h e n o t y p e s may be a d v a n t a g e o u s under e x i s t i n g e c o l o g i c a l c o n d i t i o n s and t h e i r f r e q u e n c i e s m i g h t be i n c r e a s e d u n d e r d a r w i n i a n s e l e c t i o n . C o n s e q u e n t l y t h e y m i g h t be c o n s i d e r e d as a d a p t a t i o n s . c ) F i n a l l y some p h e n o t y p i c m a n i f e s t a t i o n s might be u n f a v o r a b l e u n d e r t h e e x i s t i n g c o n d i t i o n s of t h e e n v i r o n m e n t and c o n s e q u e n t l y w i l l s u f f e r under d a r w i n i a n s e l e c t i o n and may e v e n t u a l l y e l i m i n a t e from the p o p u l a t i o n .
The p h e n o t y p i c m a n i f e s t a t i o n s and t h e i r g e n o t y p i c a l b a s i s have b e e n e s t a b l i s h e d u n d e r random s e l e c t i o n and a r e c o m p l e t e l y i n d e p e n d e n t from e a c h o t h e r . E c o s e l e c t i o n may a f f e c t them i n d i v i d u a l l y . The term " a d a p t a t i o n " does not r e f e r t o some s i t u a t i o n r e s u l t i n g f r o m s e l e c t i o n , b u t s o m e t h i n g w h i c h e x i s t e d i n c i d e n t a l l y a f t e r random s e l e c t i o n . T h i s s i t u a t i o n has been c a l l e d by some
a u t h o r s " p r e a d a p t a t i o n " .
DARWIN e s t a b l i s h e d t h e p r i n c i p l e of t h e " s u r v i v a l of the f i t t e s t " , though o r i g i n a l l y he used t h e t e r m s "of the s t r o n g e s t " . H i s f o l l o w e r s t r i e d c o n s e q u e n t l y t o i n t e r p r e t as many c h a r a c t e r s as p o s s i b l e a t t r i b u t i n g t o them s p e c i a l a d a p t a t i v e v a l u e i n i n c r e a s i n g f a v o r a b l y t h e i r f r e q u e n c i e s . T h i s h a s l e d many to u s e even a c e r t a i n f o r m of t e l e o l o g i c a l t h i n k i n g , p r e s e n t i n g t h e i r i n t e r p r e t a t i o n of f a c t s , b u t not p r o v i n g t h a t a l l c h a r a c t e r i s t i c s t h u s i n t e r p r e t e d i n f a c t improved s u r v i v a l c a p a c i t y . I n an e a r l i e r p a r t of t h i s p a p e r I t r i e d to show t h a t a p r o o f of any d a r w i n i a n i n t e r p r e t a t i o n i s a b s o l u t e l y n e c e s s a r y and t h a t f o r i n s t a n c e the a d a p t a t i o n s of o r c h i d f l o w e r s to s p e c i f i c p o l l i n a t o r s a r e g e n e r a l l y i n e f f i c i e n t . S u r v i v a l c a p a c i t y i s o n l y r e s t o r e d t h r o u g h a n o t h e r , but c o m p l e t e l y i n d e p e n d e n t a d a p t a t i o n g u a r a n t y i n g an e x c e s s i v e number of s e e d s i n each of the few f r u i t s .
We can now draw the f o l l o w i n g c o n c l u s i o n s :
I. A l l the i t e m s so f a r m e n t i o n e d change somehow the f r e q u e n c i e s of g e n o t y p e s , r e s p e c t i v e l y of the p h e n o t y p e s they c a u s e , w i t h i n a n a t u r a l p o p u l a t i o n i n f a v o r of the more f r e q u e n t o n e s . I I . The d i f f e r e n t f a c t o r s e n t e r s u c e s s i v e l y i n t o a c t i o n i n the f o l l o w i n g o r d e r : p r e s s u r e of r e c u r r e n t m u t a t i o n r a t e , i n t e r a c t i o n between a l l e l s at t h e same o r at d i f f e r e n t gen l o c i , random s e l e c t i o n and f i n a l l y e c o s e l e c t i o n , but t h e y r e m a i n i n g t h e n i n a c t i o n c o n t i n u o u s l y . I I I . As a r e s u l t t h e p o p u l a t i o n w i l l have c h a r a c t e r i s t i c s w h i c h a r e e i t h e r n e u t r a l , i . e . a r e n o t - a d a p t i v e w i t h r e g a r d t o t h e e c o l o g i c a l c o n d i t i o n s p r e s e n t , o r c a n be c o n s i d e r e d as a d a p t a t i o n s to t h e s e c o n d i t i o n s , b e s i d e s an e v o l u t i o n a r y p o t e n t i a l gen r e s e r v e , m a i n l y formed by m o d i f i e r s w i t h r a t h e r weak p h e n o t y p i c e f f e c t s .
IV. The t e r m e c o s e l e c t i o n i s used i n a d i f f e r e n t way f r o m the o r i g i n a l l y , p r o p o s e d by DARWIN. A d a p t a t i o n s a r e not p r o d u c e d u n d e r t h e p r i n c i p l e of a " s e l e c t i o n of t h e f i t t e s t " b u t a r e p r e s e n t as a r e s u l t of random s e l e c t i o n . V. E c o s e l e c t i o n d o e s not a l t e r the f r e q u e n c i e s of n e u t r a l c h a r a c t e r i s t i c s p r e s e n t , i t may i n c r e a s e the f r e q u e n c y and e x p r e s s i o n of a d a p t i v e c h a r a c t e r s , but i t w i l l r e d u c e the f r e q u e n c i e s of u n f a v o r a b l e c h a r a c t e r s or e v e n e l i m i n a t e them, u n l e s s t h e y have been compensated by o t h e r and i n d e p e n d e n t c h a r a c t e r i s t i c s .
The i t e m s w h i c h now w i l l be d i s c u s s e d h a r d l y a f f e c t the f r e q u e n c i e s of the d i f f e r e n t a l l e l s i n the g e n o t y p e but can i n f l u e n c e s t r o n g l y t h e i r h o m o z y g o s i t y and h e t e r o z y g o s i t y . The Mode of S e x u a l R e p r o d u c t i o n The mode of s e x u a l r e p r o d u c t i o n i s a n o t h e r i m p o r t a n t e l e m e n t i n e s t a b l i s h i n g m o d e l s of p o p u l a t i o n g e n e t i c s . I t has been a l s o an o b j e c t of s p e c i a l i n t e r e s t to t a x o n o m i s t who used t h e c h a r a c t e r s of r e p r o d u c t o r l a r g e l y i n d i s t i n g u i s h i n g t a x a at d i f f e r e n t l e v e l s . A l s o DARWIN and h i s f o l l o w e r s saw t h e i r i m p o r t a n c e and s t u d i e d t h e m o d a l i t i e s of s e x u a l r e p r o d u c t i o n s p e c i a l l y f r o m t h e i r p o i n t of v i e w . Somehow t h e o p i n i o n was a c c e p t e d t h a t t h e r e a r e two a l t e r n a t i v e forms of s e x u a l r e p r o d u c t i o n : a l l o g a m y and autogamy. On t h e o t h e r s i d e I came t o the c o n c l u s i o n t h a t they a r e n o t m u t u a l l y e x c l u s i v e a l t e r n a t i v e s , b u t t h a t t h e r e a r e q u i t e
f r e q u e n t l y mixed forms of r e p r o d u c t i o n i n v a r i o u s d e g r e e s of m i x t u r e between two a l t e r n a t i v e e x t r e m e s . The q u e s t i o n c a n be e a s i l y s o l v e d by a s i m p l e e x p e r i m e n t a l arrangement, u s i n g p l a n t s p e c i e s w i t h h e r m a p h r o d i t i c f l o w e r s , t h e
