The dirt is just a collection of debris over the years.
It's certainly more common with dirt roads outside, rather than it being paved and somewhere to clean back to.
Here's a good vid showing doors raised over time as the street level rises
https://www.youtube.com/watch?v=fz4ZdXpri04

For cities that have been inhabited for a long period of time, a lot of it is literally just people dropping litter, or similar. For most of the history of human cities, getting rid of waste was not something anyone really made happen, they just relied on rain to wash stuff away, and for heavier solid waste, it just sat there. If you pulled an old building down to put a new one up in its place, you would clear out the bigger bits of rubble, but a lot would just sit there, or get pushed into the street.

For a while I lived in a city in the UK with a ~1000 year old church. You had to go down four or five steps from modern street level to get to the churchyard. The churchyard and church itself have been in continual use and kept maintained over that period. That land is an example of somewhere in a built up area that has indeed been kept free from junk and debris for 1000 years.

10 heads in a row is not a big deal given enough trials... that's what happens.

We are building/living on a sea of dead debris.

If it goes far back enough you’ll have to start digging through a few thousand years of dust and dirt and so on.

I assume that you’d have to keep digging out the buildings assuming a society lived in the same buildings for those thousands of years.

Geology and specifically formations under the earths surface can provide far more detail than I.

> It may be something more akin to flipping 50 or 100 heads in a row.

50 heads in a row has a chance of 1 in a quintillion. Are you sure that's the chance to get an advantageous mutation?

[removed]

Yeah, other post above are right with the water way thing, most cities were built near the ocean or river systems on account of transportation. London goes down deeper than I ever imagined. I went 250m below street on one visit. Just fascinating what's down there.

[removed]

It’s complicated.

On the one hand, chickenpox vaccination means that there will eventually be fewer elderly people who carry chickenpox virus in their nerves, who are susceptible to virus reactivating and causing shingles.

On the other hand, it’s possible that for today’s older adults (who are too old to have been vaccinated as children) who still carry the virus, they’re exposed to less chickenpox in the environment (because fewer children are infected) so they have less immune boosting and the virus may be better able to reactivate. And in fact there has been a gradual increase in shingles for many years now, in many countries; especially in people between 30-60, i.e. those who probably didn't get chicken pox vaccine as children and who aren't old enough to get the shingles vaccine.

On the third hand, there’s apparently something else that may be increasing shingles incidence, other than vaccination. The increasing frequency started before the childhood vaccine was available, and doesn't parallel vaccine usage in general; so while it's possible that's one cause, it's not likely to be the only cause. Other explanations are basically handwaving, "better identification", or "unknown risk factors".

>One theory is that childhood varicella zoster virus vaccination has decreased the circulation of wild-type varicella virus [19, 20]. Without this exposure, the general population receives less exogenous immune boosting against varicella, increasing the risk of virus reactivation [19, 20]. However, studies have shown that the incidence of HZ has been increasing in the United States since before varicella vaccination introduction and is similar in countries with and without varicella vaccination [7, 21, 22]. Enhanced awareness of HZ by patients and healthcare practitioners, increased surveillance, and improved electronic health record coding practices are other potential drivers of the increasing number of HZ cases among middle-aged adults.

--Herpes Zoster and Postherpetic Neuralgia: Changing Incidence Rates From 1994 to 2018 in the United States

Also see

• Modelling varicella vaccination – What does a lack of surge in herpes zoster incidence tell us about exogenous boosting?
• The impact of the varicella vaccination program on herpes zoster epidemiology in the United States: a review

[deleted]

[removed]

Where cities are built on wetlands or above shallow aquifers (which historically accounts for a LOT of cities, for ease of access to water), the answer is subsidence. Soil acts like quicksand to buildings over long periods of time, if it is saturated with water. Chicago is a good modern example of this.

Related to this, researchers have found that higher temperatures cause more human males to survive gestation. They believe temperature acts as a stressor during pregnancy.

"The temperature coefficients (Table 1) suggest that a 1°C increase in annual temperature predicts one more male than expected for every 1,000 females born in a year. The median annual number of female births over the test period was 167,046. A rise of 1°C would, therefore, imply preservation of ≈167 males in the median year."

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2538905/

[removed]

[deleted]

[removed]

Imagine living in a city with no sewer system. A lot of waste is disposed on the streets regularly. I am thinking oof examples in European Antiquity here. So, in addition to chamber pots and kitchen rubbish, there would be various animal droppings. If roads are not paved, when it's the rainy season, streets become very muddy. So some more earth or gravel is put on the streets to make them less muddy. Because of This, the street level slowly rises up. So maybe what once was your ground level entrance now lies one step under the streetlevel.

When looking at the history of citis, you often find recordings of fires throughout parts of the city. Moreover, there might be destruction through earthquakes, flooding or war. When you have a lot of destroyed buildings, it is often easier to flatten the rubble out and build your new homes on top. Sometimes, the structures on the ground floor survive, but as the accumulations in the streets rose, what was once a ground floor now becomes a cellar.

Building activities without technical or mechanical help are much more difficult,

Depends on the city but many ancient cities were purposefully buried as part of expansion.

Some cities in the US are built on top of their predecessors. There are parts of downtown Seattle that are underground but accessible. You can even take a tour. Pick up "Four Lost Cities: A Secret History." It's a light history of four ancient cities that were abamdoned.

[removed]

[removed]

The mutations are random, but the fact that it’s a successful strategy is not random.

[removed]

Even today, some people have lost their driveway and walkways to overgrowth, and fallen leaves. https://youtu.be/FEI6mUmOTaI

That stuff turns to soil. Sooner or later, your Machu Picchu is covered into jungle.

Good location (waterways, trade routes) and some laziness will have builders building on top of what was once there

source for the human nasal passages thing? never heard that one before.

>in humans, all babies start off development as females.

I've seen this said a few times, and I'm always curious why the common early development pathway is considered female rather than ungendered?

It doesn't seem like enough to say that it requires activation of masculinising hormones to start being male, since presumably there are any number of hormonal triggers required on either path to spur development