Monkey See Monkey Do and Berry Eating

There is much to explore in this scene.  There’s the fur pattern of the Vervet monkey, and the beautiful color of the berries.There’s the question of what makes the berries blue, red, purple or pink?

And there’s the way monkeys imitate each other’s berry choice. When a Vervet monkey sees several others eating a blue berry, he tends to eat blue beries. If the monkey moves to a new group where they eat pink berries, the monkey starts eating pink berries. So found an experiment with Vervet monkeys. This revealed that these monkeys are susceptible to peer pressure. 



Peer Pressure

We can imagine this peer pressure as each monkey imitating the most common behavior of their neighbors. Say they have three neighbors eating blue berries and two neighbors eating pink berries. Then the majority of neighbors are eating blue berries.  

If monkeys follow the simple rule “imitate the majority of neighbors,” what would result? We can code this simple rule in Scratch to see what happens. First, we make lots of monkey “clones.” We assign a random half to eat pink, and the rest to eat blue berries. We ask all monkey clones to count neighbors eating blue and count neighbors eating pink.

If more neighbors are eating blue berries, the counting monkey will eat blue berries in the next time step. Likewise, if more neighbors are eating pink, the monkey will switch to pink.

What happens in a large group following this rule? It turns out blue and pink cluster into groups.  Blue eaters are mostly next to other blue eaters, pink eaters mostly next to pink eaters. Try the Scratch model here.


Initial random assortment of monkeys

Soon, berry eating behavior clusters

We can better see the patterns by making more monkeys and just drawing circles to represent each monkey eating that berry color. First, pink and blue berry eating monkeys are distributed randomly. After a while, pink and blues cluster.

Below is the key code. See all code and run the Scratch model here.

What might happen if monkeys have three colors of berries to choose from?

We want each monkey to switch to the berry color eaten by most of its neighbors.

Below shows the result. First, monkeys eating three colors of berries are distributed randomly (below left).

At each time step, monkeys switch to the berry eaten by the majority of neighbors.

After a number of time steps, monkey peer pressure results in clustering.

Initial random distribution.

Clustering resulting from peer pressure.

We’ll also explore the beauty of the berries and the monkeys. You can paint berries using blueberry pastes prepared as acidic and basic mixtures.

To better understand what “acid” and “base” mean, you can play around with our Scratch model of a strong acid and strong base (a simpler case  than for a weaker acid and base).  

Blueberries contain anthocyanins which are bright purple in acid environments and dark blue in more basic solutions. 

So, the blueberries serve as a rough acid-base indicator. Crushed blueberry with a little acid (lemon juice) added works as red-purple paint (we found that crushed freeze-dried berries work best to make a paint paste). With a base added, the blueberry paste works as a darker blue. We exploit that contrast to paint a blueberry!

We found that freeze dried blueberries work best. But if you prefer fresh blueberries, just crush them, mash them into a paste and use those in place of the freeze-dried blueberries described below. 


Blueberries as paint and acidity detector

The “anthocyanin” in blueberries turns red-purple in more acidic solutions. More acidity means more free hydrogen ions, causing anthocyanins to take in hydrogen ions, shifting the color towards red. If you grind blueberries and add lemon juice (acidic), it turns reddish purple.

Anthocyanins in blueberries turn darker blue in less acidic solutions. Add baking soda, which is the opposite of acidic (called “basic”), to a second batch of ground blueberries, it turns dark blue. Anthocyanins lose hydrogen ions in more basic solutions (the basic solution eats up free hydrogen ions), resulting in the shift to blue.

To better understand what “acid” and “base” mean, you can play around with our Scratch model (This Scratch model is for a strong acid and strong base, which is a simpler case  than for a weaker acid and base).   

With a spoon or back of a knife, crush blueberries in two separate bags. Freeze dried blueberries (shown in picture) work very well for this.

Spoon in some baking soda to one bag of crushed berries.

Mix in drops of water until it is has a paint-like thickness. Try painting a test spot to see how it works. Add water as needed. Squeeze the bag to mix further.

Into another bag of crushed berries, squeeze some lemon juice. 

With a cleaned paint brush, mix in the lemon juice. Try painting a spot on a test sheet of paper. You can mix further by squeezing the bag.

With the above two berry paint colors, try painting a blueberry your own way.


A Blueberry Painting Made with Blueberry Juice

  1. Make a simple shape using the red-purple acidic berry paste, thinned with water. Don’t paint areas that you want to be white. Clean brush well with soap and water. Let dry.
  2. With a clean brush, add bluish shadows with the basic blue “paint” you made with blueberry and baking soda. Use curved brushstrokes that follow the curved shape of the berry. Clean the brush with water between painting layers so you don’t contaminate the blueberry paint. Experiment!
  3. Painting acidic red-purple color over the basic blue paint increases the acidity, making it more red. See the red-purple stripes in the cast shadow of the berry (below). Play with the acid/base reactions until you get the color combination you want. Less ripe berries have more red. Ripe berries are a deeper blue. Some berries have both colors. Have fun!

4. To blend colors or soften outlines, apply clean water with a clean brush. Remove excess water with paper towel. If the color is too dark, add clean water to the painting and remove color with a paper towel.

Draw a Vervet Monkey Eating Berries

We provide this sketch outline as a start for your drawing so you can focus on the fine shades of coloring and drawing the fur patterns and textures.

We begin with the background. Simple layering of green shades in simple leaf shapes will create the vibrant, green foliage for the Vervet monkey.

Next, layering transparent colors will give the face and fur a realistic effect.

We take you from the first layers of color used to create the lush green foliage of the tree to the detailed layering of tones in the monkey’s expressive face and the texture of its soft fur.

Finally, we add the many colors of the ripening berries. 

We include a printed version of the drawing, so you don’t have to draw. You can focus on working with the online program instead and get a good result.

Step by step instructional movie below (part 1 is 13 minutes, part 2 is 14 minutes).   

Here is part one (above) and part two (below) of how to draw a Vervet monkey. You will be using kleki.com free software.