Question: Okay, I just asked a [question](https://worldbuilding.stackexchange.com/questions/82436/would-humankind-remain-the-dominat-species-in-a-world-with-twice-as-big-animals), in which mother nature transformed all animals (or brain containing living beings, if that fits better for you) into a being twice as big in order for them to kill of humankind, recovering the ecosystem.

Well, with twice the heigth, length and width, it's actually eight times the size ($2^3$).

The question was, if humankind could remain as the dominant species and the answers made it clear: Yes, easily.

But it got me thinking. Would the result be the same, if all animals would have turned twice as big at the year 0?

The rules are the same: 

* This transformation happened worldwide at the same time and only took about a minute.
* The physical abilities (strength, speed etc.) scale accordingly to the size and the animals are able to handle the gained mass just as good as their reallife counterparts.
* Mother Nature DO provide the earth with enough food to feed the bigger animals. After all, she wants to keep her children alive, killing only humankind. 
Well, carnivore don't need changes, as their prey scale accordingly. Let's just say the vegetable food grows faster, there is more of it or it provides more of whatever keeps the animals alive. (Doesn't really matter, the question is about the fight between humankind and animals)
* The earth was EXACTLY ours until the year 0.

With all that: Would humankind still be able to become the dominant species in the year 2000 (or earlier), or wouldn't they be able to handle the changes?

Answer: 
Unless the animals are magically guided to specifically attack human beings, no way.

Specifically, humans already did this once, about 12 thousand years ago. The giant ground sloths, giant rodents, regular lions and tigers on the American continent were systematically wiped out for practical or culinary reasons in the centuries following human arrival.

Humans needed flint, sticks, fire, and language. They still have all these things in the year 0, but now they also have armies, written language, boats, and metals.

If you would like a specific example: The [polar bear hunters of Zhokov island](https://polarbearscience.com/2013/02/18/the-ancient-polar-bear-hunters-of-zhokhov-island-siberia/). 397 polar bear skulls, hunted with bone and stone tools.
Pretty sure this will be closed soon. So I'll try to help you. First, you really can't just double the sized of animals and have them move or even exist the same way. As you pointed out their volume goes up with the cube while their surface area only goes up with the square. This is a big deal for energy exchange. Also, why didn't the humans double in size? Anyway, none of that really matters. Humans rule because we can manipulate tools. We routinely bring down larger animals (and sometimes fall prey to them) with all of them the size they are now. We still win. I use the term 'win' loosely here, since I can't say for certain that our reign will be as long or as fruitful as those that preceded us.

Also, if you are going to write this into a world, you should really work on your grammar. I'm not intending to be cruel here, just pointing it out. Sorry.