Reality is so varied and changing (in ways we humans will never ever be able to totally control or predict) that Evolution continuously throws up many successful ("fittest") evolving life forms to fill its many and evolving niches.
I was reminded, again, of this while reading of the terrifying battles around the Vistula River in the winter of 1945 between German Tiger II tanks and Soviet T-34 tanks.
The long gun and excellent optical sight of the Tiger II was so good it could accurately destroy the enemy's main battle tanks from distances of up to 2.5 miles ; something today's best tanks would be hard pressed to match.
High speed shells from a long gun barrel leave in a fast straight line, thus being both accurate and able to punch through thick armour, but normally both these qualities fall off quickly at increasing distances.
Close up, shorter guns firing slower shells can punch through medium thick armour with sort of acceptably accuracy.
To combat this, the Tiger II had very thick armour all around, particularly in the front, making them hard to destroy at even short distances, but also making them very slow and heavy on the ground.
But on cold hard ground they moved quickly enough and turned about quickly enough and so were able to destroy T-34s at a safe distance and get to any new locations where they were needed to stop break throughs dead.
Then the weather got warmer - now man and tank on both sides had a new misery.
They were warmer ,yes, but now their boots or tank tracks got stuck in the mud.
It proved fatal for the Tiger IIs. Fittest in the older - cold weather - niche - they proved to be unfit for the mud niche.
With the Tiger IIs stuck fast in mud due to their heavy weight, the lighter T-34s nimbly moved in behind then and destroyed them at close range through the Tiger II's thinner rear armour.
In a niche of mud, they were - temporarily - the fittest.
Despite the reality of no one size fits all, modernist armies still dreamed of producing all-arounder tanks, the "fit" for all situations instead of the "fittest for particular situations".
It is relatively easy to produce tanks with big long guns, immense armour, high speed, "low to the ground-ness" and great traction off road.
But as a result they consume lots of fuel and so have short range and a high rate of mechanical breakdowns in rough terrain : heavy and fast means pushing the finite metal strength limits of transmissions, tracks and engines.
Their weight and size makes it hard to haul them back to the rear for safe repair over wartime's normally terrible road conditions and impossible for them to cross small bridges , or be put on planes, many trains or most transporter trucks.
And they really don't like mud : their tracks are made as wide as possible to defeat mud issues given their great weight of armour and gun -- but too wide in the tracks department and their speed and fuel usage suffers.
They are ponderously might yes, but nimbly mite they are not.
And like all machines, they just sit there when out of gas - human soldiers can keep on fighting without food, their bodies wasting down to supply the missing energy.
But tanks without fuel can't waste down their armour to provide fuel and just sit there useless.
Before the Vistula battle actually began, some of the German tanks were moved into position, without using any petroleum fuel, to be used "hull down" as pillboxes, hauled there under a layer of hay by teams of Polish horses.
The mite Polish horses ambled their way to the front lines, eating their fuel along the roadside as they went : slowly and neatly confounding the German mighty....