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野生的黄瓜中含有一种很苦的物质——糖甙(dài),它可以防止其他动物吃掉它的种子,从而利于繁殖后代。在长期人工选择下,黄瓜逐渐向人需要的方向发展,苦味物质逐渐消失。但也有许多黄瓜的瓜柄处还残留一些葡萄糖甙,因而很苦。有些黄瓜不是长柄端处苦,而是整条瓜都很苦,这又是为什么呢?原来生物的演化方向有两种,一种是向前发
Wild cucumber contains a bitter substance - glycosides (dài), which can prevent other animals from eating its seeds, which will help breed offspring. Under the long-term artificial selection, cucumbers gradually evolve toward people’s needs, and the bitter substances gradually disappear. But there are also a lot of cucumber handle still some glucoside residues, and therefore very bitter. Some cucumbers are not long-handled end bitter, but the whole melon are bitter, which is why? The original biological evolution of two directions, one is forward