无生源论或化学进化论在自然科学中是指一种阐释从无机物中产生地球生命起源的理论。在米勒-尤列实验——该实验模仿了早期地球的环境，科学家发现通过与生命无关的自然化学反应能够产生被称为“生命原材料”的氨基酸。在生命体中，这些氨基酸组合成蛋白质；而蛋白质的构造则又是由核酸所决定。所以，地球上的生命是如何起源的问题最后就归结为核酸最初是如何产生的。

科学家认为地球上的首批生命应该是单细胞原核生物。迄今所发现的最古老的微生物化石距今已有35亿年，仅比地球产生稍晚数亿年。距今24亿年时，无机矿物和沉积物中碳、铁和硫同位素的稳定比例表明此间已经存在生命活动，生物标记物也证明了光合作用的存在，这些都说明此时地球上已经广泛分布着生命。

Spontaneous generation or anomalous generation is an obsolete body of thought on the ordinary formation of living organisms without descent from similar organisms. Typically, the idea was that certain forms such as fleas could arise from inanimate matter such as dust, or that maggots could arise from dead flesh. A variant idea was that of equivocal generation, in which species such as tapeworms arose from unrelated living organisms, now understood to be their hosts. Doctrines supporting such processes of generation held that these processes are commonplace and regular. Such ideas are in contradiction to that of univocal generation: effectively exclusive reproduction from genetically related parent(s), generally of the same species.