Darwin was convinced that the loss of these tastes was not only a loss of happiness, but might possibly be injurious to the intellect, and more probably to the moral character.

没人规定要一样

a loss of 损失 相当于一个动词 和might相对应

不光和而且

was not only... but might be...
前后都是be

Darwin was convinced that tastes-loss was not only a happiness-loss, but might be injurious to intellect, and more probably to moral character.