Poisonous stings

The poisonous sting has evolved at least eleven times independently:

1. in jellyfish and its relatives
2. in spiders
3. in scorpions
4. in the centipede
5. in insects
6. in molluscs (family Cone shells) 
7. in snakes
8. in the group of sharks (the rays)
9. in bony fish (stonefish)
10. in mammals (the platypus male) and
11. in plants (nettle).

When I say "independently", I mean that it has appeared in different places, in different animals, for different purposes, with different chemicals an stings, and in different epochs. In other words, it was not invented once by a common ancestor and then inherited by the kin, but devised anew eleven times to respond to the need for defense in the predator-prey fight. 
What do you think?

Agriculture and politicians

Before the invention of agriculture we were all hunter-gatherers. In a society like this, everyone must pitch in: every day you have to hunt and gather food, and it cannot be stored. This type of society does not permit the existence of "lazy" people, all healthy hunter-gatherers are required to devote much of their time to get food.

The introduction of agriculture allowed the large scale production and storage of food, facilitating, in turn, the existence of "liberated" people who did not work in the collection and could pursue other trades such as entering into politics. In a word, it allowed the existence of full-time bureaucrats and hereditary chiefs. The existence of surplus also led to the creation of taxes, of course in kind, to keep this staff not working.

These complex political units of agricultural societies are better able to wage a war of conquest than an equalitarian a horde of hunters-gatherers.

And so here we are today, where we have large production and storage, important taxes and a large number of professional bourocrats. Yes, I know whom you're thinking of: the King of Spain and his family.

Do you like hairy women?

I'm in the swimmning pool. Humans expose their skin. There is one fact which, being so widely known, no one notices: the females of the human species have little body hair. The little they have is so carefully removed. There is a whole industry devoted to hair removal. 

Are women aware of why they do not want body hair?

Darwin attributed to sexual selection the loss of body hair in humans. He assumed that ancestral males chose  females without body hair.When one sex's preferences evolve more than the other in a certain direction (in this case to hair loss), the other sex is "dragged through the slipstream". That is, partial nudity of the man had been dragged by the total nudity of women, but never fully reached it, which is why men are still more hairy than women.

Innovations in the preferences of males of a species, and corresponding changes in the appearance of female, is mutually reinforcing, in a runaway process that inextricably link them in and drag them farther and farther in the same direction. This tendency serves no compelling reason, it is merely a fortuitous path that has taken the evolutionary trend.

(In the picture: nehandertal woman)

Recommended reading: The Origin of Man by Charles Darwin

Little humans

We can say that humans have the right size to work as we do. With half of our size (in my case would be 84 cm) we could not wield a mace for hunting large animals (as the kinetic energy would decrease between 16 and 32 times), we could not bring enough momentum to spears or arrows, we could not cut or open wood with primitive tools, or extract minerals with picks and drills (all activities were essential in our historical development).

If we had the size of an ant, things would be even more complicated. Small animals live in a world dominated by surface forces that do not affect us for practical purposes. A man the size of an ant could wear clothes, but the surface adhesion forces would prevent him fom removing them. He could not light a fire, since a stable flame has to be several millimeters in length. He could mold gold leaf  thick enough to produce a book appropriate to his size, but the surface tension would prevent him from turning the pages.

Our skills and behaviors are finely attuned to our size.