[The context of this of this sutta is to invalidate the caste system and in doing so offers a rather picturesque and simple understanding of the evolutionary process in order to refuting the Brahman theory. The description is, in fact, rather similar to the modern theory of evolution although the exact details, unprovable in Buddha's time, are a little fuzzy. Incorporated in this sutta is a teaching about craving and becoming.
When people asked the Buddha about the nature of the universe and so forth, it is said that he declined, stating that he only taught that which would lead to an end of suffering. Any reference to the origin of the species would therefore have to seen in that context, and not as an independent explanation of how we got here.
In the past, that is in the 1970's and 1980's, I have studied this sutra & its topic with learned people, I have read its chinese and tibetan versions also, they differ in certain details, but the basic story exists in the chinese and tibetan canons, you have to understand that I no longer can remember everything accurately, time has passed...
This sutta has several important themes, and evolution, or devolution, is certainly one of them. The version I put there comes from http://www.urbandharma.org
, which, I think, is a good and alive buddhist organisation.
The often quoted opinion that you repeat doesn't do real justice to the Bhagavan, if you read more of the suttas in the Pali Canon, you will find that elsewhere he defines it further, and says that he does not
say that you cannot know the answer to those questions, and that on the contrary he says that you will know the answer to them as you progress on the noble path. It is a great pity that these other teachings on the topic are not equally well known !http://en.wikipedia.org/wiki/Agga%C3%B1%C3%B1a_Sutta
a good overview of the sutta