Texts 29.1a-2a

sarveṣām eva jantūnāṁ
 satataṁ deha-poṣaṇe
asti prajñā samāyattā
 ko viśeṣas tadā nṛṇām
labdhvehānte manuṣyatvaṁ
 hitvā dehādy-asad-graham
ātma-sṛtyā vihāyedaṁ
 jīvātmā sa viśiṣyate
Word for word: 
sarveṣām — all; eva — certainly; jantūnām — of animals; satatam — always; deha-poṣaṇe — to maintain the body; asti — there is; prajñā — intelligence; samāyattā — resting on; kaḥ — what; viśeṣaḥ — difference; tadā — then; nṛṇām — of the human beings; labdhvā — having attained; iha — here; ante — at the end of many births; manuṣyatvam — a human life; hitvā — after giving up; deha-ādi — in the gross and subtle body; asat-graham — an incorrect conception of life; ātma — of spiritual knowledge; sṛtyā — by the path; vihāya — having abandoned; idam — this body; jīva-ātmā — the individual spirit soul; saḥ — that; viśiṣyate — becomes prominent.
Translation: 
A desire to maintain body, wife and children is also observed in animal society. The animals have full intelligence to manage such affairs. If a human being is simply advanced in this respect, what is the difference between him and an animal? One should be very careful to understand that this human life is attained after many, many births in the evolutionary process. A learned man who gives up the bodily conception of life, both gross and subtle, will, by the enlightenment of spiritual knowledge, become a prominent individual spirit soul, as the Supreme Lord is also.
Purport: 

It is said that man is a rational animal, but from this verse we can also understand that rationality exists even in animal life. Unless there is rationality, how can an animal maintain its body by working so hard? That the animals are not rational is untrue; their rationality, however, is not very advanced. In any case, we cannot deny them rationality. The point is that one should use one’s reason to understand the Supreme Personality of Godhead, for that is the perfection of human life.