What if the earth was a DnD world?

[Steerpike]

After you get the basic sketch of the animal, it seems like you might as well just throw the MM into the trash.

I tend to agree, Polycarp. At best I think the rules ballpark how tough/dangerous a given monster is - the basic sketch as you say, which could be somewhat "ecologically relevant." But the stats rarely give any indication of things like how much and how often a monster needs to eat and drink to survive, gestation periods, sex ratios, mating habits, litter sizes, lifespans and expectancies, mortality rates amongst offspring, common diseases, and lots and lots of other super-significant things. Any attempt to construct a "speculative-realist ecology" would need to consider factors like this as much or more than how many d6s of fire-breath a creature is capable of spewing.

Also, it's worth noting that for a number of monsters, it's implied that "a wizard did it"... hence necessitating that powerful wizards capable of creating new species pre-exist the monsters.

[Xeviat]

I think the monster's stats help when comparing it to other things within the world that also have stats. Longbows deal 1d8+dex mod damage in the current edition. Using the stats of a guard, who would have +3 to hit and deal 1d8+1 damage with said longbow, a lightly trained army is going to have a hard time with a dragon. They only hit 10% of the time, so it's going to take 704 attacks from those guards to bring a dragon down. Considering the dragon's breath weapon is a whopping 90-ft cone, it's going to take a lot of soldiers. But it's not an unmanageable amount. We mustered armies of tens of thousands back in the day, and it only takes 16 years to raise a soldier instead of the 800+ years it takes to raise an ancient dragon.

It definitely means people would be very urban. Farming would be difficult, and we'd probably have ring cities like Attack on Titan. Hah.

[Polycarp]

I think the monster's stats help when comparing it to other things within the world that also have stats.

Maybe I'm unclear on the original question.

If the original question amounts to "what would historical Earth be like with dragons (or any other fantasy creature)," then stats of any kind are useless to us, because stats have no relevance outside of a game.  There are no natural 20s to help you kill that dragon; if the arrows can't penetrate the hide, they just can't, and you're going to fry, because physics is an unforgiving bastard.

If the original question is actually "what if historical Earth was literally a D&D campaign and played with D&D rules," then stats might matter, but then nothing makes sense because D&D is so remote from reality.  WW1 probably wouldn't have touched off in Belgrade in the first place, because Franz Ferdinand was obviously far too high level an Aristocrat to be killed by a single pistol shot. :P  History is totally derailed even if you don't add any fantasy elements because you've substituted game mechanics for physical reality.

[Steerpike]

WW1 probably wouldn't have touched off in Belgrade in the first place, because Franz Ferdinand was obviously far too high level an Aristocrat to be killed by a single pistol shot.

Unless Gavrilo Princip was a high-level Assassin and had used Death Attack!  :P

This almost comes down to a question of "D&D metaphysics." Are the rules in D&D the "Platonic reality" of the world whose inner logic should govern things like how societies and ecologies function, or are they the opposite - just crude mathematical models used by the DM as a means of simplifying the world for game purposes? I generally hold to the latter. A longsword doesn't "really" do 1d8 damage because it's a longsword, it cuts flesh, and damage and hit points are weird abstractions players use to gauge what's happening in the game-world rather than physical qualities that actually exist in the game-world.

[Xeviat]

... Aristocrat to be killed by a single pistol shot. :P  History is totally derailed even if you don't add any fantasy elements because you've substituted game mechanics for physical reality.

OH, definitely the real world would be using different mechanics, with attacks from surprise as auto crits and crits being essentially fatal. But Franz probably wasn't a "high level" aristocrat in 5E terms; he wasn't a hero.

Only heroes and big animals have mutliple hit dice. Remember, a standard person is walking around with 1d8 hp, which means the 1d8 longsword, even wielded by someone with an average strength, can severely maim someone with one hit, and can kill with a crit (you're insta dead if an attack drops you to 0 and deals enough additional damage equal to your max hp). With a typical person walking around with 4 HP, even a dagger at 1d4 is a threat.

Once you go past first level, the whole thing falls apart; that's where it's a game and where HP represent luck, endurance, and plot armor.

If we're going to talk about what D&D monsters would be like in the real world without some kind of metric for comparing and contrasting them, then I'm not really sure how we're going to talk about it.