The importance of these statements has sometimes been overrated and still more often underestimated. Anaximander has been called a precursor of Darwin by some, while others have treated the whole thing as a mythological survival. It is therefore important to notice that this is one of the rare cases where we have not merely a _placitum_, but an indication, meagre though it be, of the observations on which it was based, and the line of argument by which it was supported. It is clear from this that Anaximander had an idea of what is meant by adaptation to environment and survival of the fittest, and that he saw the higher mammals could not represent the original type of animal. For this he looked to the sea, and he naturally fixed upon those fishes which present the closest analogy to the _mammalia_. The statements of Aristotle about the _galeus levis_ were shown long ago by Johannes Müller to be more accurate than those of later naturalists, and we now know that these observations were already made by Anaximander. The manner in which the shark nourishes its young furnished him with the very thing he required to explain the survival of the earliest animals.[141] Footnote 141: On Aristotle and the _galeus levis_, see Johannes Müller, “Ueber den glatten Hai des Aristoteles” (_K. Preuss. Akad._, 1842), to which my attention has been directed by my colleague, Prof. D’Arcy Thomson. The precise point of the words τρεφόμενοι ὥσπερ οἱ γαλεοί appears from Arist. _Hist. An._ Ζ, 10. 565 b 1, οἱ δὲ καλούμενοι λεῖοι τῶν γαλεῶν τὰ μὲν ᾠὰ ἴσχουσι μεταξὺ τῶν ὑστερῶν ὁμοίως τοῖς σκυλίοις, περιστάντα δὲ ταῦτα εἰς ἑκατέραν τὴν δικρόαν τῆς ὑστέρας καταβαίνει, καὶ τὰ ζῷα γίνεται τὸν ὀμφαλὸν ἔχοντα πρὸς τῇ ὑστέρᾳ, ὥστε ἀναλισκομένων τῶν ᾠῶν ὁμοίως δοκεῖν ἔχειν τὸ ἔμβρυον τοῖς τετράποσιν. It is not necessary to suppose that Anaximander referred to the further phenomenon described by Aristotle, who more than once says that all the γαλεοί except the ἀκανθίας “send out their young and take them back again” (ἐξαφιᾶσι καὶ δέχονται εἰς ἑαυτοὺς τοὺς νεοττούς, _ib._ 565 b 23), for which compare also Ael. i. 17; Plut. _de soll. anim._ 982 a. The _placenta_ and umbilical cord described by Johannes Müller will account sufficiently for all he says. At the same time, I understand that deep-sea fishermen at the present day confirm this remarkable statement also, and two credible witnesses have informed me that they believe they have seen the thing happen with their own eyes. [Sidenote: Theology.]