The points are: the eukaryotic cell, multicellular life, the Cambrian, fish, reptiles, mammals, primates, tools, fire, agriculture, writing, printing, the steam engine, the telephone, the transistor, the microprocessor, the network. They are plotted against date. They fall on a line.

They fall on a line because they were selected to. The list is a list of things that are salient to a reader of the chart, and salience is denser toward the present for the same reason that a hedgerow appears denser at the horizon.

This is not a criticism of the chart. It is a description of what the chart is measuring, which is the observer’s position, plotted with great precision, at a resolution improving toward the observer.

The vertical axis is unlabelled in every printing. It has to be. There is no unit that takes the eukaryotic cell and the telephone as commensurable quantities, and the moment you supply one the chart becomes an empirical claim and stops working.

It is a mirror sold as a window. This does not make it useless. Mirrors are useful. But you should know which one you have bought before you make a plan based on what is out there.