# How many cells are there in the human body?

The other day, Amanda, who is currently teaching AP Biology, noted that among the various sources she had at hand, including a couple of textbooks, the number of cells that make up human body seemed to range from about five trillion to fifty trillion with a scattering of numbers in between. It is not clear why this number matters but I suppose if we want to impress students with the smallness of cells and the complexity of life it is worth pointing out, and if it is worth pointing out it might be worth getting it right. So, how many are there?

I believe the correct answer is in the upper end of the range Amanda cited, and here’s why.

According to various sources, the following is more or less true:

Adult people (for our present purposes) weigh between 60 and 90 kg. (I’m ignoring small populations here because this is mainly for American Audiences.) The amount of bone in a body … the non-cellular part … is between 14 and 20 percent. The amount of blood that is not cellular (i.e, that is water) is about 5% of the total body mass. The mass of a typical body cell is about one gram times ten to the negative nine, or one nanogram.

… do the math …

I get about 46 to 68 trillion.

Bigger people (using these weight ranges) would have a larger proportion of lean mass in bone, and if some off that extra mass in the range of human weights is increased fat percentage, then some of that mass is accounted for by either more fat cells or enlarged fat cells. For these and other reasons, as mass goes up the rate of additional cells goes down, so the higher end of that range is probably an exaggeration. There are other things in the body that need to be subtracted as well, including connective tissue that has very few cells in it, bacteria welcome and unwelcome alike, etc. etc.

Which brings us to a comfortable estimate of “about 50 trillion, give or take a few trillion.”

Is that satisfactory?

You can get most of the base numbers here, of course.

### Other posts of interest:

Also of interest: In Search of Sungudogo: A novel of adventure and mystery, which is also an alternative history of the Skeptics Movement.

Photo Credit: jurvetson via Compfight cc

# LeRoy Bell’s Music

As you know, my nephew, LeRoy Bell, was a contestant on the XFactor singing contest. You may also know that he was voted off the show last week. I’m not going to say much about that other than to note that LeRoy was NOT the 8th or 9th best singer in the group. He was clearly in the top three, and he was voted off prematurely. But that’s how these things work. In the end, America will Choose. A Country Western Act.

Anyway, I thought that by way of acknowledgment of LeRoy’s Talents I’d point you to his previous work. It’s all good. You can get his CD’s or download individual songs on iTunes (I assume) or Amazon or wherever you download his stuff. Personally, I like the CD’s because then I really own them.

# Mitt Romney for President!

You’ve gotta respect a guy who has no spine.

# Beep Beep!!!

The trick is, slowing them down enough, and speeding yourself up enough, then you can catch the turkeys.

Yeah, I know, it’s an ad, but it’s a good one.

# Icicles of death!

Check out this astonishing bit of film from David Attenborough:

I’m pretty sure this is from Harry Potter.

# A Tutorial in Human Behavioral Biology

If you read only one book this holiday season, make it all of the following twenty or so!

But seriously … I’d like to do something today that I’ve been meaning to do, quite literally, for years. I want to run down a selection of readings that would provide any inquisitive person with a solid grounding in Behavioral Biological theory. At the very outset you need to know that this is not about Evolutionary Psychology. Evolutionary Psychology is something different. I’ll explain some other time what the differences are. For now, we are only speaking of fairly traditional Darwinian behavioral theory as applied generally with a focus on sexually reproducing organisms, especially mammals, emphasis on humans and other primates but with lots of birds because they turn out to be important.
Continue reading A Tutorial in Human Behavioral Biology

# I want to be in charge of the music

There was a certain amount of Christmas shopping over the weekend, and I have to say the music was over the top this year. Or maybe I’m just getting more sensitive. In any event, it was driving me nuts.

So, I decided that I want to be in charge of the music from now on. And here is the playlist for the remainder of the holiday season:
Continue reading I want to be in charge of the music

# MEETUP: Friday, December 2’nd, Bar Abilene, Minneapolis

To preserve sanity in the event of changing plans or other contingencies, I’ll send you HERE to get the details. Check bat at that location for updates, should there be any.

# Be There Now: Friday, Bar Abilene, Minneapolis

This is almost like a Free Thought Blogs meetup, because there will be three or four of us Free Thought Bloggers there. If you are in the Twin Cities, go to Pharyngula and tell PZ he needs to come on over! (I have no idea what his plans are at the moment.)

To preserve sanity in the event of changing plans or other contingencies, I’ll send you HERE to get the details. Check bat at that location for updates, should there be any.

# Are you are real skeptic, or are you just faithing it

And by faithing it, I mean using faith rather than critical analysis of the available information to make important decisions about what to regard as valid.

# Kevin Drum on Black Friday’s Origin

The term “Black Friday” is said to refer to the day that so many people shop in US retail stores, the day after Thanksgiving, that retailer’s ledgers go from red (debit) to black (profit). But this appears to be a more recent use of the term which has been in use since the middle of the last century to mean something different. It was still used by retailers and other concerned with the hoardes of people shopping on Thanksgiving weekend, but not in relation to the ledger books. Rather, “Black Friday” was a bad day because it was when all those obnoxious shoppers, brats in tow, came into the downtown shops (in those days there were downtowns with shops) and annoyed everybody. And, the term seems to have been born and used for a long time nearly exclusively in Philadelphia. The term may have even started with the city police. And, the big Army Navy game held on that weekend was related to the crowds.

… all the evidence points in one direction. The term originated in Philadelphia in the 50s or earlier and wasn’t in common use in the rest of the country until decades later. And it did indeed refer to something unpleasant: the gigantic Army-Navy-post-Thanksgiving day crowds and traffic jams, which both retail workers and police officers dreaded. The retail industry originally loathed the term, and the whole “red to black” fairy tale was tacked on sometime in the 80s by an overcaffeinated flack trying to put lipstick on a pig …