The Lands of Fruit – A thought Experiment

Imagine a land of warm winters and wet summers, open plains, fertile soil and a specific family of prolific thornless bush that supplies a marvelous fruit that fulfills most of the nutritional requirements of the human body.  The various subspecies flower virtually year round.

People live in this Warm Land, and eat the fruit. They live simple lives and their population density remains low as they move about and forage for the fruit. Their lives are relatively easy, but not idyllic, there is still disease, a great scourge of the human race, especially so in such a warm wet climate.
Eventually a few groups venture outside this land, into harsher environments, including a cold land, . Here there are no simple easy fruit bushes to harvest. The ground is tougher and there is no simple bounty to be collected by moving around. At first people try to replicate the lifestyle that they had in their homeland. They find trees which grow tall, but bear fruit. Harvesting requires climbing, and those that are taller, with longer limbs are much more adept at this.
Then winter arrives, a season unknown to these people, many people die of starvation because the trees do not produce fruit in winter.
The next year, survivors collect more fruit, expending more effort, but only those who are tall enough can collect enough to survive. Now there is a bottleneck in the population. In the past, in the old land, everyone could have almost as many children as they wished, because food just required a hand with which to pick it. More children meant more hands. Now only tall ones can pick enough to sustain their families. The taller one is, the more surplus they can acquire to have a larger family. Thus those who are taller prosper and have larger families, the average height increases as those who are taller make up a larger and larger portion of the population through their posterity.

The limit to an individual’s offspring is not simply how many children he or she can have before expiring, but is now how many one can sustain with work. As with all people, this limit is to be tested, and pushed back. Methods are invented to reach more fruit, then devices are created to augment height. Those that invent these devices prosper even further and those that can use them to their fullest extent do so too. Children must be trained to use these techniques, which are a lot more complex than the simple fruit picking required in the Warm Lands.
Techniques to increase the yield of the fruit trees follow the advances in devices, and after thousands of generations the yield of fruit in the Cold Land is actually higher than that of the original Warm lands.

Now the Cold Landers re-discover the Warm Lands. They bring with them their techniques and devices, some of which are still useful on the bushes that flourish in the Warm Lands. The people of the Warm lands are made much more prosperous, but they do not rule themselves now. Those in the Cold lands harvest the fruit there. They use the increased harvest from the massive bounty of the Warm lands to feed their people back in the Cold lands and they also allow the Warm landers to take part in that increased bounty.

However, eventually the native Warm Landers they force the Cold Landers out when some of them return from the Cold lands, having learned more there. These few that went to learn in the Cold lands tell them that all people are equal, but once the tall Cold landers have left, they find that they have not the height to operate all of the devices left behind, and they lack the knowledge of all the techniques. Starvation and poverty follows, for the increased harvests allowed their population to grow further than the limit of their previous hunter-gatherer lifestyle.
For this they blame the former Cold Landers. They say that all the prosperity of the Cold lands was gained from plundering the Warm lands.

But was it?