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.

【翻译】达尔文认为，失去了这些兴趣（或鉴赏力）不仅是失去了快乐，而且可能会伤害心智，更有可能有损品德。

【分析】这是一个复合句。简单明了的理解是：

Darwin（主语）was convinced （谓语） 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.（宾语）

详解如下：

1. was convinced（系表结构），理解为“及物用法”，that从句为其宾语。在表意上相当于believed，翻译成“相信”、“认为”均可。

2. 在that宾语从句中，包含着not only...，but (also)...两个并列成分。the loss of these tastes是主语，意为“对这些兴趣/爱好/鉴赏力的丧失”。

3. be injurious to：对......有损，有害。

4. more probably to：为more injurious probably to 的省略说法。