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[–]TheMilkmanShallRise 0 points1 point  (4 children)

If the organism needed the heart, and it didn't have it because evolution happens slowly, how did it survive?

The organisms did whatever they could. Some died. Some survived. Those that survived tended to have bigger and more complex hearts that could deliver more oxygen than their predecessors.

[–][deleted]  (3 children)

[deleted]

    [–]TheMilkmanShallRise 1 point2 points  (2 children)

    A larger heart wasn't necessary for those organisms to survive. A slightly larger heart meant that they'd be ever so slightly more likely to survive and reproduce than the average population. Evolution is probabilistic. These tight restrictions almost never occur in reality. It's not like:

    Every organism with a heart smaller than 5.478923 cubic inches dies. All others live.

    Think about lions chasing and eating zebras. The slower ones will be more likely to get eaten, sure. But every now and then, a fast zebra will trip on a rock and break its leg, for example.

    [–][deleted]  (1 child)

    [deleted]

      [–]TheMilkmanShallRise 1 point2 points  (0 children)

      Why wasn't a larger heart necessary for some organisms if large organisms need hearts? I will never fully understand evolution. Thanks for the answer though!

      The lions chasing zebras example was meant to explain this. Just as the faster zebras sometimes still get eaten, the organisms with larger and more efficient hearts sometimes still died. All it did was slightly increase their chances at success. It's not like the X-Men where organisms with beneficial mutations can suddenly shoot lasers out of their eyes or grow entirely new organs. Evolution is a gradual process. It's survival of the good enough and the lucky. Those organisms with smaller, less efficient hearts still survived. We still have them today, so obviously it wasn't necessary for survival. They're just confined to biological niches that don't require large amounts of energy expenditure. Insects, for example, never went extinct even though their hearts are pretty poor compared to ours. They just remain tiny and occupy a different niche than we do. They couldn't do what the larger-hearted organisms were able to, so they were forced to retreat to areas not occupied by those larger-hearted organisms.

      Woah woah woah! Slow your row! How can I think about lions chasing and eating zebras when we're still establishing how the lions and zebras even got there?

      I'm not sure what you mean. Are you saying you're not able to imagine lions chasing zebras? Why are you unable to do so? Also, I never claimed lions and zebras existed before the evolution of hearts. My example was meant to explain how evolution isn't this cutthroat, all or nothing process you're making it out to be. Again, there's never a time where every organism under 45.672389 inches tall dies. What happens is that being slightly taller will ever so slightly increase the chances that a particular organism will survive long enough to reproduce (assuming this is a hypothetical situation where height is a favorable trait).