One theory is during a major solar event the crust of the planet becomes unstuck from the magma beneath, causing the crust of the planet to spin - with the poles moving rather abruptly to the equator, and other areas of the planet moving to become the new poles. If the theory is valid, then there are long periods where the current poles actually spend time at the equator, plenty of time for developing rain forests, human civilizations, etc. The alternative, aka, the poles not physically moving, means the planet has to massively increase in heat to allow rain forests to exist at the polar extremes. In that scenario, how hot would the equator be? Unlivable, for starters. Where would such heat come from? It would have to be caused by a massive increase in solar output from the Sun, or possibly a change in the Earth's orbit, closer to the sun. Something big, for certain.