Both. Humans have inborn tendencies to cruelty and compassion, honesty and deception, love and hate, peace and violence, and every other duality. Because both have their uses (sometimes deception or violence are morally necessary, for example). Most of what we are as moral persons is the product of our environment: how we are raised as kids, what we are taught, what we experience and learn, what we discover and realize. This process steers us more in one direction or another, or in no coherent direction at all. Accordingly, we should teach and encourage everyone to raise kids in the positive direction, and intervene when they are not. This could be done with a universally agreed set of values, like compassion, honesty, reasonableness, curiosity, courage, and self-reflection.
Humans evolved to flourish as moral persons rather than as immoral persons, so a sound and rich parental and community environment will almost always produce good people. But even then, as with defects of every other sort, physical and mental, some few will always fail to become healthy and normal. We call these persons psychopaths. But even psychopaths are not born evil. They are only born with the propensity, which must be cultivated by a bad parenting environment of inconsistent rewards and punishments. So even psychopathy could be reduced with better parenting and more school and community involvement in the upbringing of children. It could also some day be eliminated through genetic screening or genetic engineering. But ultimately, it is through improvements in parenting and school culture that we will make more good people than bad.