Darwinian orthodoxy suggests that by a gradual process of Natural Selection either one of these two types was evolved from the other, or both from a third type. I cannot imagine that anyone familiar with the facts would propose the first hypothesis in the case of _Lychnis_, nor can I conceive of any process, whether gradual or sudden, by which _diurna_ could have come out of _vespertina_, or _vespertina_ out of _diurna_. Both however may no doubt have been derived from some original third type. It is conceivable that _Lychnis macrocarpa_ of Boissier, a native of Southern Spain and Morocco, may be this original form. This species is said to combine a white flower (like that of _L. vespertina_), with capsule-teeth rolled back (like those of _diurna_).[10] But whatever the common progenitor may have been, if we are to believe that these two species have been evolved from it by a gradual process of Natural Selection based on adaptation, enormous assumptions must be made regarding the special fitness of these two forms and the special unfitness of the common parent, and these assumptions must be specially invoked and repeated for each several feature of structure or habits distinguishing the three forms. Why, if the common parent was strong enough to live to give rise to these two species, is it either altogether lost now, or at least absent from the whole of Northern Europe? Its two putative descendants, though so distinct from each other, are, as we have seen, able often to occupy the same ground. If they were gradually derived from a common progenitor--necessarily very like themselves--can we believe that this original form should always, in all the diversities of soil and situation which they inhabit, be unable to exist? Some one may fancy that the hybrids which are found in the situations occupied by both forms are this original parental species. But nothing can be more certain than that these plants are simply heterozygous combinations made by the union of gametes bearing the characters of _diurna_ and _vespertina_.[11] For they may be reproduced exactly in F_{1} or in later generations of that cross when it is artificially made; when bred from their families exhibit palpable phenomena of segregation more or less complex; and usually, if perhaps not always, they are partially sterile.[12] In a locality on the Norfolk coast that I know well, there is a strip of rough ground chiefly sand-bank, which runs along the shore. This ground is full of _vespertina_. Not a hundred yards inland is a lane containing _diurna_, and among the _vespertina_ on the sand-bank are always some of the hybrid form, doubtless the result of fertilisation from the neighbouring _diurna_ population. Seed saved from these hybrids gave _vespertina_ and hybrids again, having obviously been fertilised by other _vespertina_ or by other hybrids, and I have no doubt that such hybrid plants if fertilised by _diurna_ would have shown some _diurna_ offspring.