WEBVTT

00:00:05.690 --> 00:00:06.877
A spring fever

00:00:07.194 --> 00:00:09.997
that boost of energy,
vitality and sexual appetite

00:00:09.997 --> 00:00:11.400
associated with spring.

00:00:11.842 --> 00:00:13.888
It's been written about 
for centuries.

00:00:13.897 --> 00:00:15.045
but does it really exist?

00:00:15.351 --> 00:00:17.408
There's definately something 
in the springtime air

00:00:18.136 --> 00:00:20.099
A Canadian study showed that

00:00:20.099 --> 00:00:22.140
the rate of teen pregnancy 
peaks in March.

00:00:22.309 --> 00:00:23.702
Right around spring break.

00:00:24.043 --> 00:00:26.395
And another found, 
that men produce the most

00:00:26.395 --> 00:00:29.381
and the healthiest sperm 
in early spring.

00:00:29.550 --> 00:00:31.452
What's causing this seasonal shift?

00:00:31.743 --> 00:00:34.605
Scientists think, that our 
increased energy and better mood

00:00:34.605 --> 00:00:36.700
have to do with changes 
in hormone levels.

00:00:36.700 --> 00:00:38.460
An important one is melatonin

00:00:38.823 --> 00:00:40.638
sometimes called the "sleep hormone"

00:00:41.135 --> 00:00:43.537
It's realeased at night and 
helps us fall asleep.

00:00:43.833 --> 00:00:45.222
When the nights are longer

00:00:45.222 --> 00:00:46.601
we produce more melatonin.

00:00:46.601 --> 00:00:48.819
And in spring, as the nights get shorter,

00:00:48.937 --> 00:00:50.185
we produce less of it.

00:00:50.448 --> 00:00:53.366
Maybe explaining why we feel 
more awake and more active.

00:00:53.497 --> 00:00:56.000
Serotonin is another chemical 
that affects our mood.

00:00:56.396 --> 00:00:58.229
It's known as the "happiness hormone"

00:00:58.933 --> 00:01:01.694
And its levels arise 
in spring time as it gets sunnier.

00:01:01.694 --> 00:01:04.535
Antrophologists think that 
these changes in hormone levels

00:01:04.535 --> 00:01:06.936
may have to do with 
survival and reproduction.

00:01:06.936 --> 00:01:09.287
Many animals lay low in the winter

00:01:09.287 --> 00:01:11.404
using less energy because food is scarce.

00:01:11.404 --> 00:01:13.660
Early humans might have done the same.

00:01:13.660 --> 00:01:16.233
And when food became 
more abundant in the spring,

00:01:16.233 --> 00:01:19.035
it makes sense, 
they become more... active.

00:01:20.439 --> 00:01:22.935
Not surprisingly, 
as you move toward the equator,

00:01:22.944 --> 00:01:24.438
spring fever disappears.

00:01:24.720 --> 00:01:26.983
For example, scientists have noticed

00:01:26.983 --> 00:01:30.581
that seasonal changes in 
the birth rates of field mice flatten out

00:01:30.581 --> 00:01:32.434
as you get closer to the equator.

00:01:32.550 --> 00:01:34.219
But sunshine may not be the only

00:01:34.219 --> 00:01:35.429
springtime "pick-me-up".

00:01:35.902 --> 00:01:39.654
For humans, the optimal temperature 
for good mood is 72F.

00:01:40.133 --> 00:01:41.948
And let's face it,

00:01:41.948 --> 00:01:43.510
once the temperature starts to rise,

00:01:43.944 --> 00:01:45.680
we're wearing a lot less.

00:01:46.242 --> 00:01:48.499
For Scientific American's 
Instant Egghead,

00:01:48.499 --> 00:01:49.889
I'm Yasmin Tayag