Nietzsche on 'historical philosophizing'

An extract from the work of Friedrich Nietzsche
Egon Schiele, Portrait of Eduard Kosmack (1910)
From Friedrich Nietzsche, Human, All Too Human (translated by R. J. Hollingdale):
'All philosophers have the common failing of starting out from man as he is now and thinking they can reach their goal through an analysis of him. They involuntarily think of 'man' as an aeterna veritas, as something that remains constant in the midst of all flux, as a sure measure of things. Everything the philosopher has declared about man is, however, at bottom no more than a testimony as to the man of a very limited period of time. Lack of historical sense is the family failing of all philosophers; many, without being aware of it, even take the most recent manifestation of man, such as has arisen under the impress of certain religions, even certain political events, as the fixed form from which one has to start out. They will not learn that man has become, that the faculty of cognition has become; while some of them would have it that the whole world is spun out of this faculty of cognition. Now, everything essential in the development of mankind took place in primeval times, long before the 4,000 years we more or less know about; during these years mankind may well not have altered very much. But the philosopher here sees 'instincts' in man as he now is and assumes that these belong to the unalterable facts of mankind, and to that extent could provide a key to the understanding of the world in general: the whole of teleology is constructed by speaking of the man of the last four millennia as of an eternal man towards whom all things in the world have had a natural relationship from the time he began. But everything has become: there are no eternal facts, just as there are no absolute truths. Consequently what is needed from now on is historical philosophizing, and with it the virtue of modesty.'