humans, and many animals, have a “normal” body system, whether it’s how blood work, breathing, heart, brain or whatever… depending on each species. but what species did not have a normal body system to keep them up for a long time?
my first thought would be some hybrids, liger for example, were successful, but there got to be some different species breeding a failed species/hybrid.
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What does ‘normal’ mean?
Look at all those dogs many people love. Many of them are breeded to be basically disabled. Without a caring human they wouldn’t survive a month. Always have to think of this: https://images.app.goo.gl/FW9S9qSmymkkQ5pg9
Otherwise you may look up extinct animals like sabertooth cats or the Ground sloth which went extinct but got succeeded by other better adapted species. Even we the homo sapiens aka modern human has outperformed and finally succeeded the neanderthals.
There’s no such thing as a "normal" biological system, and hybrids like ligers are very different things to new species, but I’ll do my best to answer your question.
New species develop through the process of evolution, where gradual changes and mutations in the genetic code of an organism, over time, lead to differentiation between previously closely-related populations. As part of this process, changes and mutations that are likely to lead to the death of any organism, or decrease the chances of survival in nature (e.g. sickle cell disease in humans) will make that organism less likely to reproduce and pass on that mutation. For this reason it’s unlikely that any such change would result in the development of a new species, unless it led to an uncharacteristic survival benefit in some other way. New species often take tens of thousands to millions of years to develop to the degree that they can be classified as such. "Breeding" is also a very different process to the evolution of new species: all breeds of domestic dog currently existing are the exact same species, for example.
Pretty much by definition every species goes extinct with their "body system" – not sure they have another choice.
Any species which didn’t have basic organ functionality wouldn’t be able to stick around long enough to be a species in the first place.
To be a species you need a breeding population that’s diverse from the earlier progenitor species.
So to have a thriving population they need a stable biological system.
Now environmental conditions change and results cause some species to die out.
The Koala Bear is dying out because they evolved to feed on a very selective diet. The Eucalyptus trees are dying out due to fires and climate changes. So when they are gone so would the Koala in the wild.
The more selective and nitched a species the higher chance of extinction due to changes.
Go take a college zoology course. Or, get the textbook and read it. It’s very interesting, and will give you some perspective for your wierd question (asked by someone who needs to learn zoology.)