Nature, for the sake of evolution, wants everyone to reproduce.
In the case of fruit-plants, reproduction happens when seeds of their fruits are planted.
And since plants can’t move around planting their seeds, they depend on animals and birds.
When animals or birds eat fruits, they mostly eat their seeds too and then travel far and wide.
When these animals or birds defecate (poop) in another place, the fruit-seeds get planted in new areas with natural fertilizer and moisture, leading to reproduction.
However, these seeds would be useless if they can’t fight the acidic juices found inside the stomachs of animals and birds.
The seeds, therefore, have to develop a strong protective layer on the exterior and this happens during the last stages of a fruit’s development.
Even when the seed doesn’t have to go through the stomach acids (is dropped or thrown away), it needs a certain level of maturity before it can sprout.
Before this stage is reached, the plant must ensure that the fruit doesn’t get noticed by animals or birds; otherwise, all the energy that went into making fruit will be wasted.
So, to protect the fruits from immature consumption, plants keep them green – a color that blends with the background of leaves.
But this method may not be foolproof as some animals/birds may still find the fruit.
So, plants use a second layer of protection – during the early stages of ripening, the fruit combines certain substances (tannins & alkaloids).
These substances have a sharp and bitter taste that not only makes the fruit unworthy-of-eating but also protects it from infections.
As the fruit continues to grow, it fills itself with things like water, sugar, minerals, and vitamins; and tannins and alkaloids disappear.
The fruits also emit fragrance to attract animals and birds to eat them and disperse their seeds.
Very well explained. I love to read your posts.
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