Go to the ant, you sluggard, consider her ways and become wise (Proverbs 6:6).
The Talmud states that had the Torah not been given, we would have been held accountable to learn proper behavior from observance of lower forms of life. As Solomon says, we could have learned diligence from the ant. The Talmud adds that we could have learned modesty, fidelity, and respect of others' possessions by observing certain animals' behaviors.
We might ask: "Without Torah to teach us, how would we have known which animal traits to emulate? Perhaps we would have learned indolence from the alligator, which basks in the sun all day, and ruthlessness from predatory animals!"
People are endowed with an inherent sense of decency and morality. We are expected to use this innate power to judge right and wrong. The Torah only clarifies and emphasizes for us what we could have achieved on our own.
The Talmud thus teaches us that corruption is not only wrong and sinful, but actually unnatural. People do not sin because they have unnatural desires, but because they fail to exercise their innate intellect. If we think before we act, weighing the pros and cons of what we do, we are less likely to go astray.