May, 1932 



EVOLUTION 



Page five 



There are African plants that have inunense pulpy blos- 

 soms a foot in diameter — ugly in shape, unpleasant in color, 

 and smelling like rotten meat when the pistils need pollen. 

 They are disagreeable to human beings, but flies caimot 

 resist the odor. Flies visit flower after flower, carrying the 

 pollen that clever stamens load them with, brushing off the 

 pollen on the eager pistils. The plant b a swindler; for it 

 promises carrion on which flies can lay eggs, but it gives 

 nothing. This curious adjustment of a flower to meet the 

 instinrts of flies can only be a produrt of gradual evolution. 



Another rascally flower, in England, plays another kind of 

 confidence game. It coaxes flies to crawl down its throat. 

 They pass quite easily through a ring of hairs that point 

 downward, but they cannot climb out again because those 

 same hairs are now pointed at them and block the way. A fly 

 thus imprisoned must wait until the stamens ripen and dust 

 him with pollen. Then the flower pays its bill with a few 

 drops of nectar; the hairs shrivel up; the fly escapes and soon 

 is down the throat of another flower that captures it and 

 appropriates the pollen it brings. If all flies were teachable 

 and would not venture a second time into the kind of flower 

 that had deceived them, no such trick could have evolved. 

 Flowers have been adjusted to the peculiarities of insects. 



Sometimes the relation between flower and insect is roman- 

 tically useful to each party. An illustration is a yucca called 

 Spanish bayonet that grows throughout the Southwest. It is 

 entirely dependent for fertilization on a small white moth 

 which collects pollen, carries it to the pistil of another plant, 



and there tamps it down carefully. Why is the moth so ob- 

 liging? Because she is making a place to lay an egg. When 

 the egg hatches, the larva eats some of the seeds, but not all. 



Such a marvelously exact adjustment of plant to insect 

 seems purposeful. It is hard to believe that the moth has 

 not reasoned out what she is doing. But of course she has 

 not done, she could not conceivably do, anything of the sort. 

 For every such provident action by an insect is known to be 

 a matter of inherited instinct, which is obeyed without any 

 knowledge of what the result is to be. The instinct could only 

 have been developed by a process of evolution, in which 

 the favorable variations of stamens and pistils and egg-laying 

 desire were adjusted to each other. The plant that furnished 

 more enticing pollen would have more descendants; its type 

 would increase in numbers and would tend to produce still 

 more enticing pollen. Likewise the moth that managed the 

 pollen best was more likely to have successful descendants. 

 Each plant or insect that inherited a tendency toward better 

 co-operation was more likely to have offspring, and these 

 descendants were increasingly likely to inherit the traits that 

 made co-operation still nearer perfect. 



This theory can explain every case of the adaptations of 

 plants to fertilization by insects. No other theory can account 

 for the adaptations. If there were a botanist who rejected 

 the theory because it seemed too miraculous, he would have to 

 do his scholarly work in the dark. All his fellow botanists 

 live in the light of a theory that helps them understand how 

 nature operates. They can see how insects made the flowers. 



The Tale of the Horse 



By ALLAN BROMS 



/^UTWARDLY we see little likeness between man and not even recognised as an early horse. Now, however, we 



^^^ the horse, but inwardly they are much alike. We see, have a very complete fossil record, largely dug out of our 



outwardly, that the horse has four legs and man but two. Western bad-lands, where the arid soil lacks grass roots to 



What we forget, for the moment, is that man's arm was, not 



long ago in his evolutionary history, just a front leg which 



has become arm only recently by his uprearing to the erect 



attitude. But let a horse uprear that way, then look through 



him to his skeleton, and you will see the resemblance in 



nearly every part. Proportions have changed, especially in 



the skull, and the horse has lost some teeth, and leg and 



arm bones. Otherwise they are strikingly alike. At the 



American Museum of Natural History you can make this 



comparison, for they have mounted the skeletons of a man 



and a rearing horse side by side. The marked likeness shows 



our remote kinship, while the differences are important in 



their emphasis of the recent evolutionary changes which made 



man a man and the horse a horse. But here I will tell 



only The Tale of the Horse. 



The horse is distinctive in having but one toe to each 

 foot and in his unusual teeth. Both are parts of the same 

 story. Already, back in 1870, Thomas Henry Huxley, the 

 great evolutionist, realised what that story must be and fore- 

 told that we should find the fossil remains of a series of in- 

 creasingly horselike creatures that began with a normal five- 

 toed animal having just ordinary mammal teeth. At that Courtesy Amerian Museum of Natural History 

 time only one fossil of this series had been found, but it was Modem Horse Compared with his early ancestor, Eohippus. 



