Botanist Phil Gates explains just why crab apples have a sour taste when their cousins taste so sweet
Crab apples are eaten by birds that disperse their seeds. Because birds are insensitive to those fruits sour taste, there has been no selection pressure to evolve the ability to accumulate soluble sugars in their flesh – which is what make other fruits palatable to mammalian seed dispersers with a ‘sweet tooth’.
Research by Dr Barrie Juniper at Oxford University suggested that our cultivated sweet apple Malus pumila is not descended from the sour crab apple Malus spestris. Instead, it evolved from a distant ancestor that appeared about 10 million years ago in their droppings. With the advent of agriculture about 10,000 years ago, we began selecting even sweeter varieties from the pool of feral apples, and learned to graft them to perpetuate the sweetest.
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