Posted: May 22nd, 2023

mammals with longer sleep patterns are species whose ancestral lineage was exposed to greater pathogens

Further evidence that supports this hypothesis includes a study performed by Beizaeipour and others. This study consisted of triggering sleep response in Drosophila flies through stimulation of the immune response. Although Drosophilae are not mammal, genetically they are very similar and the results from this experiment are analogous to mammalian studies. “The observation that the immune response promotes sleep in Drosophila demonstrates an additional feature of insect sleep that is shared with that in mammals” (Beizaeipour et al 2010: 119).

In this study, scientists inoculated flies with gram-negative Escherichia coli and monitored how the immune response to infection affected sleeping patterns. Sleep state was indicated by zero activity in the flies. According to results, Drosophila was found to enter a sleep state within one hour following bacterial inoculation. Control flies with little or no infection spent an average of twenty minutes in a sleep state. On the other hand, infected flies showed sleep states averaging to ninety minutes. These results are rather astounding considering the short lifespan of Drosophila.

These findings support the conclusion that sleep enhances immune defense. Because animals subject themselves to this dormant low energy state, the mammals channel resources internally and “adapt” to the selective pressures exerted by pathogens infecting bodily systems. It is possible that antigenic challenge from pathogens selects for increased white blood cell counts, which ultimately selects for increased sleep length.

Therefore, mammals with longer sleep patterns are species whose ancestral lineage was exposed to greater pathogens. Figure 2 illustrates the findings of Barton and others, which shows the direct correlation between white blood cell count and length of sleep in the studied mammals. Additionally, figure 3 shows the correlation between bacterial infection and Drosophila sleep period. As you can see, pathogens play a significant part in mammalian sleep patterns.