Humanoid and Planet

I understand that you might think "2 circulatory systems require more oxygen so obviously it is not useful." but I know my Kepler Bb humanoids inside and out from anatomy and physiology(including how they form antivenom and antipoison via their own immune system) to development from pregnancy to adulthood.

I also know their planet inside and out(well maybe not the whole planet since I haven't mapped it all(haven't found a good 3D mapping software yet)) from their seasons and transition phases(like sprummer(transition phase between spring and summer)) and how long they last in kepler days and earth days(Kepler days are 1/3 longer than earth days) and thus the year length to the different biomes on this planet and what they are like during these seasons and transition phases.

Anyway here is the circulatory system in detail.

Humanoid Circulatory system

This actually comprises of 2 separate but connected circulatory systems. First off, their right circulatory system(which is only called that because of their right heart being the pump for it) is just like our single circulatory system with 4 pulmonary veins, a pulmonary artery, an aorta to the left, and venae cavae to the right and a 4 chambered heart.

Now their left circulatory system is inverted. The left aorta is to the right of the left heart. Right in the center of their chest are blood vessels connecting 1 aorta to the opposite heart via coronary arteries. So the left aorta supplies the right heart and the right aorta supplies the left heart. These are like backups in case the primary coronary arteries don't work but they also keep the heart strong, even in the worst cases of heart attacks and help the heart completely heal from a heart attack.

Now all of this means that the heart rate doesn't need to be as high to supply more oxygen as it does in the average human. The blood pressure is higher because of there being twice as many blood vessels(not counting the extra coronary arteries. Oxygen supply is higher and CO2 levels are lower. If 1 circulatory system shuts down completely, the humanoid will survive and still be healthy as long as their other heart is strong. So 1 circulatory system down does not mean heart disease.

Pros and Cons


Complete healing of heart No turbulence between circulatory systems Higher oxygen transport No heart disease unless both hearts are bad


Possible but unlikely, 2 different blood types in the same person. Makes blood transfusions extremely complicated since you would have to know which blood vessel is bleeding and thus which blood type to use on the spot and without testing, there is no guarantee. Heart problems more difficult to treat

So I see more pros than cons with this double circulatory system.

Kepler Bb is earthlike but with higher amounts of both oxygen and carbon dioxide(so a thicker atmosphere of basically the same air).

So is this double circulatory system actually useful?


2 Answers 2


In order for two redundant circulations to develop and be retained by evolution, there must be an actual need for the redundancy. Otherwise genetic errors that make one of the systems malfunction would be retained and you'd end up with a single higher capacity and reliability system. If the two hearts are right next to each other and in fact directly connected this is extremely unlikely. Indeed you might want to rewrite your description so that each heart is fully independent otherwise a failure in one heart will cascade to the other and you have a needlessly complicated and inefficient heart with double the chance of failure of one. (I think I got what you meant anyway, so no big deal, but..)

Instead you might want to have single circulation with multiple independent and physically distributed hearts and redundant paths with valves to restrict damaged portions to minimum pressure needed for healing.

  • $\begingroup$ The hearts are separate. When I say separate but connected I mean the 2 circulatory systems supply the same organs not direct connection via anastomosis to the blood vessels from separate hearts. The extra coronary arteries are there for a reason(healing from vascularization and more stem cells in circulation). Plus I see a problem with 2 independent hearts in 1 circulatory system. Heart failure would happen at the same time in both hearts(or very close) and there would be turbulence(so constant carotid bruit) $\endgroup$
    – Caters
    Jun 24, 2016 at 20:24
  • $\begingroup$ Not only that but the heartbeat would most likely not be in sync later on in life, even if it was at birth. With 2 separate circulatory systems the heartbeat would most likely always be in sync unless there is a type of arrhythmia. $\endgroup$
    – Caters
    Jun 24, 2016 at 20:33
  • $\begingroup$ If you have two hearts next to each other in essentially same conditions, you will always have a chance of cascading failure. The systems need to be physically separated. And there really need to be more than two. Otherwise the increase in load after one fails nearly guarantees a cascade. Also if the systems or hearts need be in sync or can cause turbulence to each other that also will cause cascading failures, instead of adding redundancy you would be increasing your vulnerability footprint. Such a system would not evolve IMHO, so best assume the system isolates the hearts from these effects. $\endgroup$ Jun 24, 2016 at 20:41
  • $\begingroup$ <- Not really related to my answer, just a general observation of such systems in response to your comments. $\endgroup$ Jun 24, 2016 at 20:42

Redundant systems always have the issues that come with every continuously operating redundant system. That being said, I don't see a reason why a species cannot evolve to possess such as system if the benefits surpass the extra energy to operating the system. In electrical engineering, we oft use multiple paths due to the material degradation of using one path being too much or a single path cannot communicate enough data. The same will apply to only pipeline, even blood vessels


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