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Recently, I learned that pandas have a carnivore's digestive system but that it exists almost exclusively as a herbivore. If pandas hunted would they be able to find meat in their environment? Can't think of any reason why they would 'evolve' to eat only bamboo if this was true. It's like 2 million years ago some bears decided they wouldn't hunt, hibernate or even roar and are slowly committing suicide.

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    $\begingroup$ Keep in mind that evolution is not directed. The bears didn't "decide" anything. Natural selection operates when certain genes confer certain traits that end up increasing fitness of the organism. As it happened, for pandas in their environment, eating bamboo and not hibernating were traits that were beneficial, so they persisted in the population. $\endgroup$ – C_Z_ May 20 '15 at 16:34
  • $\begingroup$ My question was why becoming bamboo eaters was beneficial. Is there no game in the environment that they can hunt? $\endgroup$ – Anoop Alex May 21 '15 at 15:07
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    $\begingroup$ Why all the downvotes? I find it quite an intriguing question, given that they are on the verge of extinction. $\endgroup$ – AliceD May 21 '15 at 15:16
  • $\begingroup$ i was interested because pandas do still eat meat from time to time for example when they find a dead carcass. They are still omnivores. So I wondered if they are too lazy to hunt for live meat, lost the instinctual skill or there is no game in their habitat. $\endgroup$ – Anoop Alex May 22 '15 at 3:01
  • $\begingroup$ I find the first two options very unlikely since as far as I know humans are the only animals that don't live instinctively. $\endgroup$ – Anoop Alex May 22 '15 at 3:20
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First: My opinion on why the question has received that many down votes

There were many down votes to this question, not because the question is no of interest. The question actually makes sense and is interesting. The post attracted those down votes because the post and the comments of the OP shows little understanding of evolutionary processes. Here are some issues:

  • some bears decided. Evolution is not directed. There is no conscious decision from any species (except humans, see eugenics) on how to evolve.

    • as far as I know humans are the only animals that don't live instinctively. I am not sure there is a common definition of the word "instinctive". But I very much think that the vast majority of people would suggest definitions that forces us to accept that humans behave instinctively. And if the definition would accept that human can sometimes not behave instinctively, then the definition will very likely accept that some animals behave instinctively.

    • why they would 'evolve' to eat only bamboo. Why did you use quotes?

Eventually the question may show lack of effort as showed in the fact that the OP is stating the 2MYA the panda and the other bears diverged, while it was rather about 36 MYA (according to onezoom and even a bit older according to this reference). This paper however shows that pandas had an omnivorous acenstor 7 MYA only suggesting that pandas modern day diet has evolved less than 7 MYA. More information below.

I don't think that those evident misunderstandings deserves receiving down votes (not sure though).

Can't think of any reason why they would 'evolve' to eat only bamboo

I had a quick look and I didn't find any good answer to your question. It seems that:

  • In nature pandas has diet consisting almost uniquely of bamboo (ref). They can eat any of the 25 species of bamboo wiki.

  • Pandas have a digestive track that is very short (like most carnivorans and unlike most herbivorous). Because of their short digestive track they eat a lot (between 9kg and 14kg of bamboo per day!) and they poop a lot (40 times a day) wiki!

  • As a consequence of its diet, the panda spend little energy and avoid any effort wiki.

  • Pandas seem to have evolved so that it is able to digest cellulose with the help of bacteria (ref, ref). According to wiki and BBC this microbiome is not herited from the mother but is acquired later in life (it is quite common to see that). This paper suggests that having such a fast transit prevent the ability to absorb other nutrients and therefore limits the benefit of having a more diverse source of food.

  • pandas size and mouth are adapted to their diet. They have a large size and a round face with powerful jaw wiki.

  • We actually know what genes are responsible for food preference in pandas (ref). The mutation for the "I prefer bamboo" allele is estimated to be 4.7 MY old (consistent with skull observation ref).

  • According to many comments online and according to wikipedia (but I couldn't find a trustful reference), as observed in zoo, pandas can eat other stuff when available. Citing from wikipedia While primarily herbivorous, the giant panda still retains decidedly ursine teeth, and will eat meat, fish, and eggs when available.

Given the amount of information we're having there may be tons of possible scenarios. It is possible for example that there is inter-species competition in the wild for access to prey. It is possible that there was for some point a very low density of preys and pandas has shifted their diets. Once, pandas had evolved some features of herbivorous species, they would get stuck there and not be able to get back to a meant based diet (stuck onto a local optima on the fitness landscape). There might be many different explanations involving patterns of competition, parasites, sexual selection, etc... And it seems that we haven't been able to disentangle between all of these.

Hope that helps!

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  • $\begingroup$ I admit the term that of "decided" was wrong. I know evolution is not conscious. My main point was that a species with so many traits negative to survival shows that survival of the fittest is not a hard rule. Census evidence is now showing minor hope that pandas may not be facing extinction since poaching has been reduced since the population has even INCREASED 17% over last 10 years. $\endgroup$ – Anoop Alex May 29 '15 at 6:38
  • $\begingroup$ You post positive evolution mostly related to diet. I can post negative aspects related to reproduction also. Did you know that females select only one mate during the tiny heat period and will let all cubs but one die usually? $\endgroup$ – Anoop Alex May 29 '15 at 6:46
  • $\begingroup$ here is my blog re it although u will see me assuming spiritual awareness behind evolution though i dont really believe. Just that survival of the fittest is not a hard rule. There is survival of the unfittest too. epilepsydubai.wordpress.com/2015/05/22/panda-evolution $\endgroup$ – Anoop Alex May 29 '15 at 6:51
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    $\begingroup$ Yes. The question was not about panda's biology in general (and hopefully because it would have been too broad) so I did not address pandas reproduction. Btw, many species have similar pattern of letting all the cubs but one dying. Cub cannibalism is not rare either. The expression "Survival of the fittest" was coined by herbert Spencer who has little knowledge about evolutionary biology. Intuitively, "survival of the fittest" relate to the process of natural/articial (eventually sexual as well) selection. $\endgroup$ – Remi.b May 29 '15 at 13:39
  • $\begingroup$ In those terms, then the adage "survival of the fittest" is indeed not a hard rule as not being the only rule, or if stated more correctly, natural selection is not the only process governing evolutionary processes. However, your simple observation of pandas lifestyle is not a demonstration of those other processes. Evolutionary biology is a big field of science. For example, I am personally working in the subfield of population genetics working on the evolution of the species range, the process of range expansion and the evolution of the mutational effects. $\endgroup$ – Remi.b May 29 '15 at 13:40
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At approximately the same time that they switched to a primarily herbivorous diet, pandas lost the ability to taste "umami," or "savoriness." We don't know whether this happened before or after the dietary change, but the umami flavor is a strong attractant for other meat-eating omnivores, like humans. It signals instinctively that a food is exceptionally valuable and should sought out and prioritized over other available food. This is why your mouth waters more at the smell of a steak than the smell of a carrot. Unable to distinguish this quality by smell/taste, pandas would be less inclined to go to the effort to hunt down or scavenge meat, compared to just stuffing readily available but almost inedible bamboo into their craws for sixteen hours a day, even though it often gives them serious indigestion and limits their ability to travel or reproduce.

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    $\begingroup$ Hi Edie. Welcome to Biology S.E. :)..any chance you could back up your answer with a (couple of) source(s)? I would recommend to have a quick read through the BioSE Tour (biology.stackexchange.com/tour).. in doing so you'll also earn your first badge. $\endgroup$ – Johnny Jul 3 '17 at 16:08

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