How Many Monkeys

Every week at the Thursday Night Volunteer Repair Parties at Bike Works, we put down the tools for a few minutes to introduce ourselves and chat a little. There is always a question for each person to answer to help get to know people, to get us talking. Usually it's a bicycling question, but not always. Sometimes it's very serious, other times funny, often it's about a favorite food or favorite ride.

A couple of weeks ago a volunteer named John asked the group this question:
How many monkeys do you think there are in the world?

It was a fun question.

There were guesses as high as 3 billion and as low as 100,000. Most people guessed between 5 and 80 million. I guessed "under one million". But here's the thing: John doesn't know the real answer, he just uses it as an ice breaker.

 Well, this data geek couldn't let that THAT go... so when i got home i started searching and creating a data model. I surveyed the primate fact sheets at animal info.org and the Univ of Wisc Primate Info Net. I included some mathematically modeled estimates since some species don't have detailed population numbers on the factsheets, but the numbers seem pretty solid.

There are three genii of primates: Lemurs, Monkeys (distinguished by having a tail) and Apes (distinguished by not having a tail). I have removed one of the species of ape from the totals, and have listed it as separate category: Homo sapiens.

There are 67 species of monkey. I found primate fact sheets on 24 of those species (18 of which are endangered).  There are currently 826,166 individuals among those 24 species. Mathematically modeling (using the median), for the species missing fact sheets, gives an estimated total of about 950,000 monkeys in the world.

There are 15 species of ape (excluding humans). I found primate fact sheets on 10 of those species (9 of which are endangered). There are currently 691,525 individuals among those 10 species. Mathematically modeling (using the median), for the species missing fact sheets, gives an estimated total of about 810,000 apes in the world.

There are 24 species of lemur. I found primate fact sheets on 4 of those species (almost all of the 24 are critically endangered). Among those 4 species there are currently 51,180 individuals. Mathematically modeling (using the median) for the species missing fact sheets gives an estimated total of about 100,000 lemurs in the world.

There are roughly 7,100,000,000 humans in the world.

So i found that there are several answers to John's question. How Many monkeys are there in the world?

• 950,000 - if we use only the genus Monkey.
  
• 1,750,000 - using the standard colloquial definition, (monkeys and non-human apes).
  
• including Lemurs, there are just under 2 million non-human primates in the world.
  

It's very disturbing to me that on this planet for every monkey there are about 3,800 human beings!!!

	distinction	species w #	species	actual count	est total (using median)
monkeys	have tail	24	67	826,166	950,000
apes	no tail	10	14	691,525	810,000
total		34	81	1,517,691	1,760,000
lemurs	3rd family	4	24	51,180	100,000
humans	apes			7,100,000,000	7,100,000,000