[LukeL]

Explain how a basic (relatively speaking) 2-chamber heart circulatory system can evolve into the very complex 4 chamber or double heart system.

[neverdem]

Lungfish

[BRK]

Explain how a basic (relatively speaking) 2-chamber heart circulatory system can evolve into the very complex 4 chamber or double heart system.

You don't have to explain it, just draw a sweeping arrow on a chart between the two. Sort of fade the start end, and that's all you ever need.

[Rebel_Ace]

A plausible explanation might be that a genetic mutation causes multiple "two chamber" hearts to form, much in the same way that similar genetic "misfires" cause people to have six fingers, or three sets of teeth.

With a "double pumper", an organism might have better survival traits, and the genetic "defect" is preserved, and futher mutates into the 4 chambered hearts we see today.

[muawiyah]

First, it becomes a 5 chamber heart system ~ like crocodiles have. The rest is simple.