user176: If Buddhism is a general theory of understanding the cycle of attachments, is it possible that any other 'wise' enough creature could achieve the same thing? 
In the Visuddhimagga English translation,  a creature who can understand this theory is called 'a wise man'.
In the Visuddhimagga Sinhalese version,  a creature who can understand this theory is called as a creature with 'Trihethuka Pratisandi'. i.e. Tri (three) + hethuka (caused by factors) + Pratisandi (birth): 'A birth caused by three factors' (Pali: tihetukapa.tisandhi).

user111: Only humans and the beings in the higher realms can attain enlightenment. Except for the ones in certain Brahma realms.  Some beings in the lower realms may hear the Dhamma, memorise it and be born in higher realms as a result. 

user114: Yes, you need to be human. 
The Buddha even made the famous simile of the turtle in the ocean that comes up for air once every century and, when it does, happens to put its neck through a yoke floating around in the same ocean. He said that that's how lucky you are for having been born a human, so you shouldn't waste this opportunity to work towards enlightenment.
If you're another kind of sentient being, you'd better hope that you're reborn as a human in your next incarnation.

user98: Kôdô Sawaki said: 

"All creatures are Buddha already, but it is the human alone which
  needs to express his Buddhaship every day".

I don't know if this originate in a teaching of Gautama Buddha or if it is Sawakis interpretation alone. However I understand it like all humans are Buddha by default, as all other animals. But humans might "lose their way" and so its their practice alone to return to the Buddhaship.
That for me also means that animals do not need to understand Buddhism, because they are already Buddha. Understanding also would mean to try thinking about it. I doubt animals do that, and if they could, I doubt they see any benefit of trying to understand anything which is "just there".
We humans try to understand Buddhaship, as we can loose this state of mind. Bodhidharma once said, we do no need to understand Buddhism, because we would never understand as long as we want. Instead we just need to practice Buddhism, which will make you understand.
(I am practicing Zen, thats why my response might be from a view from the Zen angle)

user7909: Perhaps the question needs to be clearer. Are you talking of Buddhism as in the teachings of the Buddha or Buddhism as taught by the two main branches (Mahayana and Theravada) which could be said to be the interpretation of the teachings of the Buddha, often blended with cultural influence?
I have a pet corn snake and she could be considered to be in a mindful state for much of the time - she neither cares about the past nor fears for the future. She hunts when she's hungry and rests when there is no need for her to move. She never appears to be dissatisfied, she has no attachment to physical things and she does not crave anything beyond her basic needs for survival. By that definition, has she not already achieved Nirvana?
The challenge to human enlightenment is that we do crave, we do form attachments to experiences and possessions and we constantly experience dissatisfaction with our life experience. Can an animal that exemplifies the four noble truths be said to understand Buddhism? Not really - they are as they are - they have no need for Buddhism nor an understanding of it.  

user10193: Maybe only a Buddhist can understand Buddhism.
But enlightenment, do you think that an Asian have more chances to reach enlightenment than a European?
Anything based in the impermanence of our senses and mind will produce more ignorance.
This is also ignorant but I prefer lo live in a world where the enlightenment it is reachable from any living or not living form, and right here, right now.

user18: Actually, the restriction has nothing to do with being a human; it has, as the Visuddhimagga notes, everything to do with the rebirth-linking consciousness (patisandhi). Nor does it relate to "understanding Buddhism" per se, but rather attainment of samatha jhana and nibbana. Only a being who is reborn with all three of the wholesome roots - non-delusion (amoha), non-greed (alobha), and non-anger (adosa) can attain absorption (jhana), the path (magga) or fruition (phala).
Types of beings that may be born with these three roots are humans, angels (deva) and gods (brahma). Animals, ghosts and hell beings are not.
For more information, here's a good summary of the types of rebirth based on number of roots:
http://www.wisdomlib.org/buddhism/book/abhidhamma-in-daily-life_2/d/doc3181.html

176: <p>If Buddhism is a general theory of understanding the cycle of attachments, is it possible that any other 'wise' enough creature could achieve the same thing? </p>

<p>In the Visuddhimagga English translation,  a creature who can understand this theory is called 'a wise man'.</p>

<p>In the Visuddhimagga Sinhalese version,  a creature who can understand this theory is called as a creature with 'Trihethuka Pratisandi'. i.e. Tri (three) + hethuka (caused by factors) + Pratisandi (birth): 'A birth caused by three factors' (Pali: tihetukapa.tisandhi).</p>
 111: <p>Only humans and the beings in the higher realms can attain enlightenment. Except for the ones in certain Brahma realms.  Some beings in the lower realms may hear the Dhamma, memorise it and be born in higher realms as a result. </p>
 114: <p>Yes, you need to be human. </p>

<p>The Buddha even made the famous simile of the turtle in the ocean that comes up for air once every century and, when it does, happens to put its neck through a yoke floating around in the same ocean. He said that that's how lucky you are for having been born a human, so you shouldn't waste this opportunity to work towards enlightenment.</p>

<p>If you're another kind of sentient being, you'd better hope that you're reborn as a human in your next incarnation.</p>
 98: <p>Kôdô Sawaki said: </p>

<blockquote>
  <p>"All creatures are Buddha already, but it is the human alone which
  needs to express his Buddhaship every day".</p>
</blockquote>

<p>I don't know if this originate in a teaching of Gautama Buddha or if it is Sawakis interpretation alone. However I understand it like all humans are Buddha by default, as all other animals. But humans might "lose their way" and so its their practice alone to return to the Buddhaship.</p>

<p>That for me also means that animals do not need to understand Buddhism, because they are already Buddha. Understanding also would mean to try thinking about it. I doubt animals do that, and if they could, I doubt they see any benefit of trying to understand anything which is "just there".</p>

<p>We humans try to understand Buddhaship, as we can loose this state of mind. Bodhidharma once said, we do no need to understand Buddhism, because we would never understand as long as we want. Instead we just need to practice Buddhism, which will make you understand.</p>

<p>(I am practicing Zen, thats why my response might be from a view from the Zen angle)</p>
 7909: <p>Perhaps the question needs to be clearer. Are you talking of Buddhism as in the teachings of the Buddha or Buddhism as taught by the two main branches (Mahayana and Theravada) which could be said to be the interpretation of the teachings of the Buddha, often blended with cultural influence?</p>

<p>I have a pet corn snake and she could be considered to be in a mindful state for much of the time - she neither cares about the past nor fears for the future. She hunts when she's hungry and rests when there is no need for her to move. She never appears to be dissatisfied, she has no attachment to physical things and she does not crave anything beyond her basic needs for survival. By that definition, has she not already achieved Nirvana?</p>

<p>The challenge to human enlightenment is that we do crave, we do form attachments to experiences and possessions and we constantly experience dissatisfaction with our life experience. Can an animal that exemplifies the four noble truths be said to understand Buddhism? Not really - they are as they are - they have no need for Buddhism nor an understanding of it.  </p>
 10193: <p>Maybe only a Buddhist can understand Buddhism.
But enlightenment, do you think that an Asian have more chances to reach enlightenment than a European?</p>

<p>Anything based in the impermanence of our senses and mind will produce more ignorance.</p>

<p>This is also ignorant but I prefer lo live in a world where the enlightenment it is reachable from any living or not living form, and right here, right now.</p>
 18: <p>Actually, the restriction has nothing to do with being a human; it has, as the Visuddhimagga notes, everything to do with the rebirth-linking consciousness (patisandhi). Nor does it relate to "understanding Buddhism" per se, but rather attainment of samatha jhana and nibbana. Only a being who is reborn with all three of the wholesome roots - non-delusion (amoha), non-greed (alobha), and non-anger (adosa) can attain absorption (jhana), the path (magga) or fruition (phala).</p>

<p>Types of beings that may be born with these three roots are humans, angels (deva) and gods (brahma). Animals, ghosts and hell beings are not.</p>

<p>For more information, here's a good summary of the types of rebirth based on number of roots:</p>

<p><a href="http://www.wisdomlib.org/buddhism/book/abhidhamma-in-daily-life_2/d/doc3181.html">http://www.wisdomlib.org/buddhism/book/abhidhamma-in-daily-life_2/d/doc3181.html</a></p>
