In the field of astrobiology it's become received wisdom that complex-celled (eukaryotic), multi-cellular life is not as adaptable or as tough as microbial life. As a result, when scientists discuss the planetary requirements for life, they typically divide environments into those that are somehow 'stable' enough for complex life, versus those that might support microbes but not much else.

Long-term climate stability is one factor that is thought to matter a lot, and especially climate linked to the variations in a planet's rotational and orbital configuration. Here on Earth we're subject to the Milankovitch Cycles, a set of interlinked and overlapping periodic variations in properties such as orbital ellipticity, axial tilt, and axial precession (where the Earth's axis points at given times in its orbit). These cycles exist because of the gravitational interactions of the Earth and all the other objects in the solar system - like the Moon, Jupiter, Saturn, and so on.

The net result is that for at least the past few hundred thousand years Earth's climate state has been driven (in a major part) by these configuration shifts that change how solar radiation hits the planet. For example, the geological record of ice ages shows good correlation with the Milankovitch Cycles.

However, compared to the spin-orbit variations that could happen to a rocky planet, the Earth seems to suffer only a mild case of these perturbations. For example, Earth's axial tilt only shifts back and forth by a couple of degrees over time. It's long been pointed out that it's the specific Earth-Moon configuration that helps prevent the Earth's spin axis from undergoing much more extreme variations. By comparison, the planet Mars sees its polar axis vary by tens of degrees over just a few tens of thousands of years. And many distant, rocky exoplanets could also suffer these kinds of instabilities.

The idea that Earth's mid- to long-term climate variation is 'just-right' for complex life has sometimes been extended to argue for an anthropic selection effect, and used to support the idea that complex life may have very few opportunities to establish itself across the universe.

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