# 8 Billion and Growing

Sometime late last year the human species reached a new milestone: there are now over 8 billion people living on Earth! This is more than double the population that existed fifty years ago, and our species doesn’t seem to have any plans to stop there. In fact, maybe demographers, experts in the study of statistics relating to human populations, predict that we will hit 10 billion people sometime in the 2050s.

The reasons for the population increase make a lot of sense. Better access to medicine and more effective treatments have decreased child mortality and increased people’s life expectancy. At the same time, better sanitation has led to a higher quality of life, while increasing crop yields have helped to feed the surging population in many countries. Interestingly, most experts expect the population increase to slow over the next few decades, before eventually capping around 10.4 billion people in 2100.

One thing that many people have in common is difficulty in visualizing large numbers. A small group of 5 friends, a classroom with 25 students, and even an assembly with 500 students make sense, but things start to get harder to visualize after that. An outdoor concert might have 5000 attendees, while some of the largest sports stadiums hold around 100,000 fans. This method, breaking down large numbers into a more commonly encountered scenario can be a great strategy for visualizing data. However, things start to get even more difficult when we start dealing with numbers in the billions and beyond. Here are a few crazy numbers about humans:

• 3.72 × 1013 – The estimated number of cells in the human body
• 1× 1014 – The estimated number of neuronal connections in a human brain
• 3.22 × 109 – The total number of base pairs in the human genome
• 2.5 to 3 x 109 – Total heartbeats in a lifetime

It can be enlightening to think about these sorts of huge numbers as you work through biology labs. How many bacteria are in a colony (~3.3×109, in case you are curious)? How many copies of a plasmid are in a solution, or how many strands DNA did you load into an agarose gel? How many individual antibodies are found in each well of your ELISA plate? Let us know if you have a favorite biology number!