Another argument that creationists use regarding the flood is population statistics. Here is a summary of the argument that I received in a post from a creationist. I was able to find the original source which I’ve referenced.
"World population growth rate in recent times is about 2% per year. Practicable application of growth rate throughout human history would be about half that number. Wars, disease, famine, etc. have wiped out approximately one third of the population on average every 82 years. Starting with eight people, and applying these growth rates since the Flood of Noah's day (about 4500 years ago) would give a total human population at just under six billion people. However, application on an evolutionary time scale runs into major difficulties. Starting with one "couple" just 41,000 years ago would give us a total population of 2 x 10^89. The universe does not have space to hold so many bodies."
I can't help but point out that this is really a uniformitarian argument from people who protest against uniformitarianism.
The larges problem with this argument is that we know that the human population did not grow at all for much of human history!
The reason this statement is true is because, before the invention of agriculture about 12,000 years ago, humans were hunter-gatherers. Hunter-gatherers forage and hunt in a particular area without domesticating either the plants or the animals in that area. That sort of society is necessarily largely migratory. Once the food supply gets small in the area where the group is currently residing, it must move to another area.
Migration causes problems for growing populations. As a population gets larger, they have to migrate more often because the amount of food in any area stays constant but the larger population uses it up at a faster rate. If they migrate more often, they must migrate over a larger area. Inevitably they run into other migrating bands of humans who don’t like the intrusion. Those contacts result in battles which tend to keep the population down.
Migration is also difficult for families with a number of smaller children. Most human migration was by foot which meant that small children had to be carried. A single individual can’t carry large numbers of children. Typically a single parent can only carry a single child over long distances. Even more typically only the women carry a child. Therefore a family in a hunter-gatherer society is restricted to one child at a time that cannot walk long distances on its own. In order to allow the family to survive, the horrendous practice of infanticide was often practiced by these migratory humans in order to keep the populations in check.
Simply put, hunter-gatherer societies require stable populations with effectively zero growth rates. The rate of population growth in the 21st century is due to modern agriculture but also to the industrial revolution allowing much more widespread distribution of foods.
Another problem for the population growth argument is that it actually underestimates the human population at various times throughout human history.
Basically what the creationists are doing is taking two points – a population of only eight people in 2600 BCE and a population of 6 billion in 2000. Then you apply a single geometric growth curve that matches those two numbers. Then voila!
But that same growth curve gives population estimates for interim points as well. Here are some that are not realistic:
1. The Great Pyramid was constructed in 2566 BCE. According to the formula, there were 17 people alive on Earth at that time.
2. The Trojan War took place in 1185 BCE. At that point there were only 5000 people alive on the entire Earth.
3. The First Olympic Games took place in 776 BCE. There were only 32,971 people alive on the entire Earth at that time.
4. In 28 BCE, the Emperor Augustus had a census of Roman citizens. He counted 70 - 100 million people. Yet according to the creationist formula, only 586,678 people were alive on the entire Earth.
The problems are obvious; none more so than having the Great Pyramid built when there was a world-wide population of only 17 people! Any consistent population growth rate beginning from only eight people 4500 years ago simply doesn’t work.
A final point: if such statistics really could be used to determine things such as the age of the Earth, then none of us is more than a few days old! That’s because all of us have E coli bacteria in our guts. Such bacteria can reproduce more than once an hour. If you were to count the number of E coli bacteria in your body and use the same sorts of population growth calculations that Henry Morris uses, if we were more than a week old then our bodies should contain nothing but such bacteria! Clearly that is ridiculous.
 Morris, Henry, Scientific Creationism (El Cajon, CA: Master Books)
 http://www.rtis.com/nat/user/elsberry/evobio/evc/argresp/populate.html, referenced on April 29, 2008