Yes, this notion has been thrown out there again, so why not make a separate topic of it.
First off, I'd like to say that this thought is part of a string of thoughts often uttered when someone says they're atheist. You'll often also hear: "How can you be moral without God? What's stopping you from lying, stealing, killing, etc. if there is no God?"
It's a little scary that intelligent, thinking, adult people can ask such questions. But, all those questions boil down to a few common points that I'll try to cover in this post, and that's why I will concentrate on the topic title question, as the answer to that will touch on all of those.
So, the question is: "If evolution is true, we are nothing but animals, so what's to keep us from behaving like animals?".
Indeed...
- I think we can all agree that we all "came from" babies; we have all at one point been infants. If that "theory" is correct, what's to stop us from behaving like babies? What's to stop us from throwing temper tantrums, lie on the floor kicking and screaming, run around like crazy, hit and spit on and steal from others and be possessive (as children often do when unsupervised), babble and scream, and pee ourselves?
Could it be that we have grown, we have changed, we have developed into adults, both physically and mentally? And that because of this, we have responsibilities toward others, and other and better ways of expressing ourselves?
Someone (a theist) here posted: "We might as well lose a few more brain cells and go and live in a jungle with our ape cousins." Yes, and similarly we might as well lose a few brain cells and become like babies again, in constant need of care from others. Are we "just babies"? Are we "just animals"?
Now - you may say: "Yes, but you're just proving my point with this, because as babies we had parents and others who taught us, just like God "taught us" to be human. Evolution can't account for that".
Well - evolution is that "parent". Not that evolution is an entity, but the way evolution works, the positive characteristics (for survival, health and prosperity) in a population are kept while the negative tend to die out. This may seem to be countered by what we see every day, in that 'evil' people seem to thrive and become rich etc., but over time and large populations, most people are after all altruistic, kind and loving at least to their families and mates, and this altruistic (as opposed to selfish, 'evil') way of treating your family, your tribe etc. tend to be carried over to the next generation. It's a good thing for the survival of the individuals of the 'tribe' and thus the 'tribe' as a whole. Chaos is not.
What exactly does it mean to "behave like animals"?
I have seen animals show expressions of compassion, love, hurt, sorrow, fear, pride, anger, joy, companionship, protectiveness, ingenuity, skill... All of them "human" characteristics, but to a different degree than in us. I would rather call them all "animal characteristics which are often more evolved in humans".
"But humans are not animals - we are elevated to a different level - we are spiritual creatures".
Yes - animals do not and cannot appreciate art, music, poetry, history, beauty etc. the way that humans can (or at all). So yes, humans are different from animals.
Similarly, babies do not and cannot appreciate art, music, poetry, history, beauty etc. the way that adults can (or at all). So yes, adults are different from babies.
The difference lies in level of development. As adults, we have developed the capacity to appreciate all those things babies can't.
As human beings, we have developed higher intelligence and self-awareness/consciousness that makes us able to appreciate all those things animals can't. We are not (solely) governed by instincts anymore.
Granted - animals can be violent, murderous, "immoral"(!), etc. But are those things not found in humans as well? But usually, in humans, they are suppressed or done away with altogether because we are "grown ups". We can plan for the future, and therefore know our actions will have consequences outside of the act itself.
So - morality then:
(Some) animals are 'immoral' by human standards. What are the human standards of morality, though? The human standards change through time, place, culture, religion and situation. Once, polygamy was not considered immoral. Later, it was (in some places). Once, slavery was OK. Today, it would be considered immoral and wrong. Once, women were more or less property. Not more than about 100 years ago (depending on country) they were not considered fit to vote. In most of the world, this would now be considered wrong.
What about killing, lying, stealing, cheating?
Do we really need a God - a "parent" - to tell us these things are wrong? Why are they wrong? Solely because a God said so? This God would have to have a reason, though, right? It would be logical to assume that laws were given by God because they would be good for us, both as individuals and as a society, not for some arbitrary reason, right? If you give your children rules, they are probably there to protect them and help them, not because you simply want to exert power over them?
So.
These things then are not wrong simply and only because God says so, but because they would have negative consequences in the short and/or long term, on an individual or societal level. Therefore - they are just as wrong through an evolutionary world view (if they can be shown to have negative consequences).
Beauty then? What is the purpose of beauty from an evolutionary view point? What is beauty? Beauty is a subjective - but often still common - rating of how appealing an object (or subject) is. In animals, driven by instincts, beauty in a potential mate is a sign of good health and survivability. "Beauty" there is what is colorful, fully formed, elaborate - any sign that the potential mate is healthy. Humans, because of their intelligence, self awareness and detachment from pure instincts, may transfer this to any object, like a beautiful painting or a sunset.
Now - from a theist's point of view, this may seem rather 'dull' and uninspiring.
But is 'beauty' more beautiful if there is a God? What is the 'opposing view' to evolution here? The other explanation? The 'opposing view' of the theist is that what is beautiful is what God has told us is beautiful. Or to put it more delicately and poetic; "What God has bestowed on us". Being created by a God, we have then been 'programmed' with a set of "rules" for what things we should consider beautiful, since we are created in God's image. If you are a theist and disagree with this, then you too will have to come up with a non-theistic theory of why we find certain things beautiful. If not God-given during creation of mankind, then why and how exactly? If God-given, we have just as little say in what is beautiful as with evolution theory, and no explanation of why.
Becoming an atheist is far from easy. As a post-theist atheist, you do not simply toss out everything you've ever learned about morality, what's right and what's wrong. To the contrary - in the process, you find yourself constantly coming across topics you once had a sure-fire answer to: "God has said...". As an atheist, when those topics come up - arbitrarily and infrequently and as a surprise - you suddenly have to come up with a reason of your own for why this specific action should be considered right or wrong. And you may find that you disagree with "your former self" - but some times you may still agree. And you may even disagree with other atheists.
What is morality? What is it that is moral? As mentioned - this depends.
-Say you went to a country where scratching an itch was considered falling for temptation, and you came from a country where doing so is perfectly natural. Even when trying to live by that country's rules, it's almost inevitable that you would eventually - without even thinking of it - scratch an itch. In doing so, you would be considered weak and immoral in this country, and you would be met with appalled looks and raised eyebrows. You would perhaps tell them "Sorry, but scratching an itch isn't hurting anybody?", and they would answer "First of all, this is God's law, and He knows what's best. And besides - if you continually scratch an itch, your skin will be damaged, and you will be more prone to disease. If we all did it, the whole community would be at risk".
So - it depends.
In the above scenario, the atheist may scoff at the "It's God's law" explanation, but might agree in theory with the other explanation. He would still continue to scratch his itches at home though, because he knows that in most cases, with limited scratching, there would be no danger to him or the community. He has come to his own conclusion based on what's real and applicable to him, not by some divine, rigid, dogmatic law unchanged for centuries.
This is what the atheist has to do constantly. At least if he/she has had a different world view before, as most here have. Following the above illustration it should also be added that if you are the one defining what is to be considered immoral, you'll have no problems finding immoral people.
One could go through most or all other characteristics in the same manner as I have done with 'beauty' and 'morals' above; love, poetry, music etc. The question would be: Are these things more amazing or great if there is a God out there? Are they less amazing or great to the atheist? Less important?
How come God is the full stop answer? If it originates from God it's great, but if it originates from our own experiences over thousands of years, it's not? If a very powerful entity tells us how and what to think, that's great, but if we came to these conclusions based on experience, it's not?
Can evolutionists just as well behave like animals, since they say we came from animals? Are they trying to make a monkey out of you?
Can adults just as well behave like infants since they 'came from' infants? Are adults trying to make an infant out of you?
No - we have grown to another level of consciousness and responsibility, not by supernatural means, but natural, both as adults and as humans.
Can theists just as well behave like God since they say we came from God?
[edited] Sorry, I see now that I may have been equaling evolution with atheism a little too much in this post; after all there are many Christian and other theist evolutionists. I write from my own point of view. [/edited]