In 1887, 28-years after the publication of Charles Darwin’s “On the Origin of Species,” The San Francisco Chronicle declared:
“The modern game of baseball is one of the most convincing proofs of the doctrine of evolution. All the leading features of that theory—natural selection, differentiation of species and the survival of the fittest—are admirably illustrated in the game of baseball as played at present. It is admitted that baseball originated with the game of town ball, or rounders, and some future Darwin of the diamond field may publish ponderous folios to exhibit the various steps by which the childish game of rounders developed into the scientific sport now so popular.”
Charles Darwin
That evolution, said the paper, was also seen in the popularity of the game:
“The permanence of baseball as a game is now firmly established. It has grown into the affections of sport-loving Americans as thoroughly and absolutely as cricket is the object of English admiration. As evidence of this it is stated that on Decoration Day 96,000 people attended three games of baseball in and near New York City.”
Despite the popularity of the game, the paper noted there was some pushback against “scientific baseball:”
“The most unfavorable criticism which has passed upon the present game is that it has become a ‘battery game;’ that is, all the playing is done by the pitcher and catcher. The object of late years has been to keep the score of runs down, and to that end the rules have been framed in the interest of the pitcher and catcher…and scores of one to one and one to nothing have not been uncommon. Now this is very scientific, but the people who pay their money to see baseball played have become tired of it and want to see the field have something to do. They want to see more batting and base running and larger scores.”
The Chronicle said, in order to increase offense, “The National League and American Association, appreciating this state of things has recently adopted some new rules.” Among the rules instituted for the 1887 season were the reduction of the pitcher’s box to 5 ½ feet by 4 feet, five balls rather than six for a base on balls, and four “called strikes” for a strikeout:
“The opinions of expert players as to the effect of the new rules differ, although most agree that the game will be of more interest to the spectators and will draw better and the gate money be increased, a question of interest to all the clubs except the purely amateur ones. “
Whatever the result of rule changes, this further evolution and the game’s “manly qualities” were reasons baseball had earned its place in American culture:
“It would be hard to find a sport which brings into play the manly qualities of wind and muscle to greater advantage than baseball. No one but a skilled athlete can play the game successfully, and training men for a baseball campaign has become almost as much a science as training them for a boat race or a foot race. Eye and nerve, lungs and heart, legs and stomach must all be capable of doing their duty and doing it well to make a good baseball player. There is generalship too, in the game, and many matches are won by superior skill, even though handicapped by inferior strength. The game well deserves its title of the national game, and bids fair to excite more interest and attention year by year.”
Baseball History Daily 
Darwin would have loved the bat flip as well!
According to the rules timeline in Total Baseball, the pitcher’s box was shortened from 7 feet by 4 feet to 5.5 feet by 4 feet in 1887. And of course the pitcher’s rear foot had to be on the rear line of the box, establishing the 55.5 foot pitching distance.
Thanks. I just looked again and realized I wrote that incorrectly, looked at the Baseball Almanac rule timeline and wrote 4 feet from 5 1/2 in my notes instead 4 feet by 5 1/2.