The basic building blocks of humans are cells. When embryos are first fertilised, they're all the same. But after three weeks, they begin to specialise and clump together to form the various bits of the body. 

人体结构最基本的组成是细胞。当胚胎刚受精时，它们的细胞是完全相同的。但三周后，细胞会开始分化并分别凝聚形成人体的各个部分。 

The secret to learning how humans are built [lies] deep in the heart of these cells. Specifically, the Human Cell Atlas project aims to find out which genes are turned on at what times and in which locations. Researchers have now published details of how this happens in skin. This raises the possibility of eventually slowing down the signs of ageing. 

了解人体构造的秘密就藏在这些细胞深处。具体来说，人类细胞图谱项目的目标就是找出基因会在何时何处被激活。研究人员目前已经公布了这一过程在皮肤中如何进行的细节。这一发现可能增加了最终延缓衰老迹象的可能性。

词汇表

building blocks 基本组成
cells 细胞
embryos 胚胎
fertilised 受精
specialise （细胞）分化
clump together 聚成一团
Atlas 图谱
genes 基因
ageing 衰老，老化