Caption: The speciation of vertebrates in the later part of Devonian period (420--360 Myr BP). Shown are the descendants of pelagic lobe-finned fish including early tetrapods and other lobe-finned fish (see also Wikipedia: Evolutionary history of life: Colonization of land).

Features:

1. Included in the diagram is the tiktaalik (a species representative of the transition from fish to amphibian) and an ancient coelacanth (which has descendants enough like it that we call them all coelacanths). Modern coelacanths are arguably living fossils. Most professors are too.

2. The evolution of tetrapods (i.e., four-limbed vertebrates and their descendants) in the Devonian period (420--360 Myr BP) may have been required the Moon to have more or less the size and orbital parameters it does have.

   This idea has led to an anthropic principle argument to explain the great coincidence: the near equality of angular diameters of the Sun and Moon. See the file sun_moon_angular.html for an discussion of the great coincidence.

3. The anthropic principle argument for the great coincidence is given by Steven A. Balbus 2014, http://arxiv.org/abs/1406.0323, Dynamical, biological, and anthropic consequences of equal lunar and solar angular radii.

   In brief, Steven A. Balbus's (1953--) argument is that great coincidence is a consequence of the need for large tidal variations in the Devonian period (420--360 Myr BP). The large variations were needed to strongly favor the evolution at that time of tetrapods: i.e., four-limbed vertebrates and their descendants including humans with sufficiently advanced astronomy to notice great coincidence.

   Thus, the fact that we tetrapods are here now explains in a sense great coincidence.

   For more on the anthropic principle, see IAL 0: A Philosophical and Historical Introduction to Astronomy: The Anthropic Principle.

4. However, the anthropic principle argument just accounts for the relative near equality of the angular diameters. The fact is present very near equality must still be a bit just a great coincidence.