A religious sect that contends that space travelers created the human race by cloning themselves declared Friday that the first cloned human had been born, but it offered few details and no evidence to support the claim.

答案：
A religious sect that contends that space travelers created the human race by cloning themselves declared Friday that the first cloned human had been born, but it offered few details and no evidence to support the claim.

要点：句子的框架是A religious sect… declared … that …, but it offered…。这个句子中，由but连接了两个并列分句。在前一个分句中，由that引导的定语从句that contends that… by cloning themselves修饰先行词a religious sect，而定语从句中又包含了that引导的宾语从句作动词contends的宾语。

译文：一个宣称人类是由外星人克隆而成的邪教组织于星期五宣布第一个克隆人已出生，但它没有谈及过多细节，也没有提供任何证据。