When fall starts, and the weather starts to get colder (or its supposed to) and you notice that the way the earth looks is changing, you may notice that your mood has also changed substantially. As the seasons change, so do the way humans act, feel and interact.

According to LiveScience, “There is evidence of seasonal peaks in suicides, which occur more frequently in summer, and birth rates, which also tend to peak in spring and summer. Both, however, are influenced heavily by other factors, according to a chapter on chronobiology that Provencio contributed to “Comprehensive Textbook of Psychiatry” (Lippincott Williams & Wilkins, 2008)”

There is actual  scientific evidence that humans are more likely to get less happy during the fall and winter season. According to a study on human behavior based on seasons, humans are more likely to suffer from seasonal affective disorder, or SAD starting during late fall and early winter. “A 2001 study published in the journal Archives of General Psychiatry, found that people suffering from SAD secreted the hormone melatonin for longer periods during winter nights than during summer nights, a fluctuation also seen among mammals whose behavior varies seasonally. Normally, human production of melatonin, which regulates sleep and is called the hormone of darkness, does not vary with the seasons.” says Life Science.
Science can also explain why some people can stay up at all hours of the night, whereas others have to be in bed before midnight. “Everybody’s clock doesn’t tick on a 24-hour rotation, however. The average human day – as generated by our primary circadian pacemakers, called the suprachiasmatic nuclei and located in the hypothalamus of the brain – lasts about 24 hours and 11 minutes, although it can be longer or shorter for individuals. Light “resets” this internal clock, so our bodies are in synch with the time of day, according to Provencion.” This explains why some people are more likely to stay up at all hours of the night. They have a longer natural cycle. ” says Life Science. As daylight savings occurs and the nights get longer and the days get longer, this affects how the human population and animal population functions.

“Scientists have shown that mood can change with the seasons, as well as metabolism (it’s easier to gain weight in the winter). The activity of human genes also changes with the seasons, and so can immune system activity,” says the Huffington Post. The study also talks about how even the way humans perceive colors changes from summer to winter.

You may not have even realized that your mental state or physical state has been changing though the seasons, or maybe you never really understood why you were more sad during the winter, but now you know, you could just be suffering from SAD, or Seasonal Affective Disorder.