There's no 'ism' like sexism

In German man is not the same as Mann, and Germans presumably have no PC qualms about words formed with the morpheme man (if there are any – my specialist knowledge of German is limited, but the same must apply to many other words derived from PIE languages)  that refer to humanity as a whole..

In English, though, things are not so clear. On the one hand, traditionalists who insist on chairman to refer to a woman protest on linguistic grounds that the suffix -man does not refer to the gender of the occupant of that position (ignoring the fact that centuries of Anglo-Saxon culture have exploited just this ambiguity). On the other hand, strident feminists perpetrate linguistically naïve solecisms like herstory. Many English speakers insist on using chair, in the chairman case, when a woman takes the position (often betraying their cause by reverting to the [apparently] gender-marked form when the woman chair is replaced by a man).

<irrelevant_quibble water_holding="not really">
If a female chairman is a chair, what's a female spokesman? A spoke?
</irrelevant_quibble>

What can be said in public has certainly changed in my lifetime; but that 65 years is only a fairly placid codicil  to a much longer story. Here's what happened to mankind.

The 65 years from 1708 to 1773 marked a rise of many times the rate of recent decline (by eye, I'd estimate that the early rise is about six times as steep as the recent decline).

Meanwhile, what has happened to the PC replacement for mankind? It was fairly (surprisingly?) popular in the 18th century, but then tailed off throughout the 19th and most of the 20th. Then, in the late 1980s, the frequency rises steeply. It is tempting to think that the decline in mankind is directly related to the rise in humankind.

But on that scale, the demise of mankind looks terminal.  It was so popular in the late 18th century that at the beginning of the 21st it looks nearly extinct.  If you take a step forward (if you'll excuse the art gallery metaphor) and look more closely at the latest numbers (as shown on the right), the story is not quite so clear. They have fallen all right, but they have levelled off.

Presumably this means that there there are some dyed-in-the-wool mankind-users who have been unaffected by the rise in humankind.

But this isn't raking up the accursed sycamore seeds that threaten to increase the (already extreme) bio-diversity of my "lawn".

b
PS And here's a clue:

Can Mister Messy be the guilty party? (9)

Update: 2016.11.11.18:15 – Added PPS
PPS I meant to add that all those word frequency graphs come fro the Collins English Dictionary.  Sadly, they stop  at 2008, and the axes aren't usefully labelled.

Update: 2016.11.14.11:45 – Reinstated the latest picture (which was there once, but had disappeared).