The old replaces the new
Used to reference the fact that new things grow and replace old things. Also refers to metabolism in biology
Neutral
世界上总是以新的代替旧的，总是这样不停地新陈代谢 | Shìjiè shàng zǒng shì yǐ xīn de dàitì jiù de, zǒng shì zhèyàng bù tíng de xīnchéndàixiè
All over the world, new things always replace old ones. It's always developing like this
[Source]
它促进新陈代谢，让人感到更有活力 | Tā cùjìn xīnchéndàixiè, ràng rén gǎndào gèng yǒu huólì
It speeds up the metabolism and makes people feel more energetic
[Source]
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This is an HSK chengyu
Uncertain -- Either my resources all attributed this chengyu to different people or this information has been lost to history
This origin of this chengyu is uncertain, so I won't associate it with any particular story