This old common question is still not clear to me. I got this explanation:
Bananas go through a unique process known as negative geotropism. Instead of continuing to grow towards the ground, they start to turn towards the sun. The fruit grows against gravity, giving the banana its familiar curved shape.
But why? The answer lies in the botanical history of the banana. It originated in the middle layer of the rainforest, where there is little sunlight. If the fruit were to grow towards the small amount of light that penetrates sideways through the vegetation, the plant could overbalance and topple over.
So bananas developed a way of growing towards the light without destabilising the plant.
So, evolutionarily, the bananas are 'forced' to grow towards the light. But how is this capabilty 'grown into' the banana? Is it something epigenetic or is it just light that attracts them? So how does this mechanism works?