I was trying to think of parallels in nature to the human city, where a species can completely rearrange its environment.  Does an ant colony get close to that?  Digging tunnels and caverns, stockpiling food, growing gardens?  A colony does have a remarkable resemblance to a city, but I think it stops at the structural basics.  The human city is on a scale of influence that its functioning affects a far greater number and variety of flora and fauna.  Monstrous constructions of concrete, pavement, and steel wind across the surface of the earth, creating a sinuous solid tube of noise, rubber grit, and exhaust.  Cities displace streams, rivers and create their own weather as parking lots and concrete absorb and release more heat than trees, grass and water.  Exhaust gasses from vehicles, 5 lanes wide and at a dead stop, collect in valleys near the cities, showing as the brown haze in the air and poorer health in the local flora and fauna (including humans).  Leaving city boundaries, sometimes even by as little as 30 minutes, can feel like a completely natural environment with no human influence ever before.  I've been mountain biking and hiking on the North Shore of Vancouver for 14 years now, and I'm always amazed where I find decade old tree stumps, lumber harvested in a forest full of trees you can't wrap your arms around.  I grew up in Alaska where you can find rockpiles, paths and even old vehicles in remote valleys.  And now, with global warming (assuming the debate about whether it is of natural original or from human efforts settles on the human symptom), I think it is safe to say that nowhere on this planet has been left unaltered, except maybe the darkest depths of the ocean.

I can't condone a complete dismissal of the city.  Take 6.5 billion people, spread them across the Earth's 150 million square kilometers of land, and you'll find 12.5 thousand people per square kilometer.  Each person gets 78 square meters, basically a 9x9 meter (30ft) square.  Ugh.  Amusingly, that is about 1/4 the size of a standard house lot in 'downtown' Vancouver.   Imagine having to ask for permission to cross a chunk of land every 9 meters.  Europe's densification is impressive.  Cities stop at farm fields, reducing the suburban sprawl, and suburban commute.  But my answer isn't densification (though that definitely helps), my answer is to weigh what I eat, what I consume, what I purchase against a 'need' and a 'why.'  It is far from foolproof, and can backfire, but it keeps me conscious of my rate of consumption, the rate of how fast I use my earth and pump effects back into it.  So much of human society is based on growth.  Growth of assets, growth of families, growth of societies.  The Earth doesn't grow as fast as we do, the rainforests don't expand at the same rate as our cities.  I would think that if human growth was paced to the ancient, ever changing but inexorably slow genetic adaptation machine, that human influence wouldn't be as adverse, that the Earth could play the dynamic card and throw in an ice age or two to slow us down.  We aren't giving her the chance to even think about playing that card, unless she has some surprises up that atmospheric sleeve.

I have to smile when I think of the estrogen and testosterone bumping and grinding against each other.  That play, that game, is too successful within the creativity of the human race to protect its proliferation.  Humankind is playing the game of genetics and biology that created it, but with an overwhelmingly successful disregard of the ebb and flow of food and shelter that binds other species.  At least, a disregard for the ebb and flow of food and shelter until we run out of room on this limited ecosystem of rock and carbon known as Earth.