Explain how Sinclair, with his image of the tree, makes a connection between the evolutionary theory of Charles Darwin and the workers in Packingtown.

Sinclair uses the example of the trees to describe how Packingtown becomes a case of "the survival of the fittest."

Now the dreadful winter was come upon them. In the forests, all summer long, the branches of the trees do battle for light, and some of them lose and die; and then come the raging blasts, and the storms of snow and hail, and strew the ground with these weaker branches. Just so it was in Packingtown; the whole district braced itself for the struggle that was an agony, and those whose time was come died off in hordes. All the year round they had been serving as cogs in the great packing machine; and now was the time for the renovating of it, and the replacing of damaged parts. There came pneumonia and grippe, stalking among them, seeking for weakened constitutions; there was the annual harvest of those whom tuberculosis had been dragging down. There came cruel, cold, and biting winds, and blizzards of snow, all testing relentlessly for failing muscles and impoverished blood. Sooner or later came the day when the unfit one did not report for work; and then, with no time lost in waiting, and no inquiries or regrets, there was a chance for a new hand.