Average brain weights (grams) of mammals

Five selected mammals

Mammal Brain weight
Asian elephant 4603 g
Chimpanzee 440 g
Arctic fox 44.5 g
Ground squirrel 4 g
Mouse 0.4 g

On the original scale, it is impossible to get any idea of the distribution of brain weights of the smaller mammals — the skewness of the distribution prevents the smallest crosses from being distinguished. Click on crosses to identify the mammals with the biggest brain weights.

The top scale shows the logs (base 10) of the weights — click crosses to explain this.

Drag the slider to 'linearise the log axis'. The resulting dot plot is what would be obtained with a standard dot plot of the log data. Explain how this separates out the smallest mammals, allowing us to see whether there are clusters or outliers.


Select Five selected mammals from the pop-up menu. These five mammals have brain weights that differ by a factor of about 10 from each other. On the log scale, these mammals are (approximately) evenly spread out.

The complete data set contains 'average' brain weights of 62 selected mammals. (The author has no idea why these particular mammals were chosen in the original publication.)

The reduced data set contains brain weights of 5 mammals that differ by a factor of approx 10 from each other.