- 
spring fever 
- 
that's full of energy, vitality 
- 
and sexual appetite associated with spring 
- 
it's been written about for centuries 
- 
but does it really exist? 
- 
there's definitely something in this spring time air 
- 
a Canadian study showed a way that 
- 
teen pregnancy peaks in March 
- 
right around spring break 
- 
and another found that men 
- 
produce the most 
- 
and the healthiest sperm 
- 
in early spring 
- 
what's causing this seasonal shift? 
- 
Scientists think our increase in 
- 
energy and better mood 
- 
have to do with changes in hormone levels 
- 
an important one is melatonin 
- 
sometimes called the "sleep hormone" 
- 
it's released at night and helps us to fall asleep 
- 
when the nights are longer 
- 
we produce more melatonin 
- 
and in spring, as the night gets shorter 
- 
we produce less of it 
- 
may be explaining why we feel 
- 
more awake and more active 
- 
seratonin is another chemical 
- 
that affects our mood 
- 
it's known as the "happiness hormone" 
- 
and it's level risens in spring time 
- 
as it gets sunnier 
- 
and the pathologists think that 
- 
this changes in hormone levels 
- 
may have to do with survival and 
- 
reproduction 
- 
many animals lay low in the winter 
- 
using less energy because food is sacarce 
- 
early humans might have done the same 
- 
when food became more abundant in the spring 
- 
and it make sense that they become... 
- 
more.... 
- 
active 
- 
not surprisingly 
- 
as you move toward the equator 
- 
spring fever disappears 
- 
for example 
- 
scientists have noticed that seasonal changes 
- 
and the birth rates of field mice 
- 
flatten out 
- 
as you get closer to the equator 
- 
but sunshine may not be the only 
- 
spring time "pick me up" 
- 
for humans, the optimal temperature for 
- 
good mood is 72 degrees Fahrenheit 
- 
and let's face it 
- 
once the temperature starts to rise 
- 
we're wearing a lot less 
- 
for Scientific Americans and Instant Egghead 
- 
I'm Yasmin Tayag