The possibility of biological transfer between planetary bodies is seldom factored into life detection strategies, although the actuality of such an event would have profound implications for how we interpret potential biosignatures found on other worlds. This article addresses the possibility of life on Mars in the context of a biological transfer and an independent genesis of life. The phylogenetic tree of life on Earth is used as a blueprint to interpret evidence of life and as a guideline to determine the likelihood that potential biosignatures could be expressed by martian organisms. Several transfer scenarios are considered, depending on the timing of transfer with respect to the evolution of life on Earth. The implications of each transfer scenario and an independent genesis of life on the biochemical nature of the resulting martian organisms are discussed. The analysis highlights how conceding the possibility of a biological transfer has practical implications for how we search for evidence of life, both in terms of the quality of potential biosignatures and the likelihood that certain biosignatures might be expressed. It is concluded that a degree of uncertainty on the origin of martian organisms might be unavoidable, particularly in the absence of a biochemical context.

中文翻译：

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火星上的生命：独立起源还是共同祖先？

行星体之间生物转移的可能性很少被纳入生命探测策略，尽管这种事件的实际情况将对我们如何解释在其他世界发现的潜在生物特征产生深远的影响。本文讨论了在生物转移和生命独立起源的背景下火星上生命的可能性。地球上生命的系统发育树被用作解释生命证据的蓝图，并用作确定火星生物可能表达潜在生物特征的可能性的指南。考虑了几种转移情景，这取决于与地球上生命进化有关的转移时间。讨论了每个转移场景和独立生命起源对由此产生的火星生物的生化性质的影响。该分析强调了承认生物转移的可能性对我们如何寻找生命证据具有实际意义，包括潜在生物特征的质量和某些生物特征可能表达的可能性。结论是，火星生物起源的一定程度的不确定性可能是不可避免的，特别是在没有生化背景的情况下。在潜在生物特征的质量和某些生物特征可能被表达的可能性方面。结论是，火星生物起源的一定程度的不确定性可能是不可避免的，特别是在没有生化背景的情况下。在潜在生物特征的质量和某些生物特征可能被表达的可能性方面。结论是，火星生物起源的一定程度的不确定性可能是不可避免的，特别是在没有生化背景的情况下。