0:00:05.700,0:00:06.670
spring fever

0:00:07.069,0:00:08.669
that's full of energy, vitality

0:00:08.928,0:00:11.338
and sexual appetite associated with spring

0:00:12.072,0:00:13.742
it's been written about for centuries

0:00:13.742,0:00:14.822
but does it really exist?

0:00:15.032,0:00:17.992
there's definitely something in this spring time air

0:00:18.082,0:00:20.132
a Canadian study showed a way that

0:00:20.382,0:00:22.022
teen pregnancy peaks in March

0:00:22.142,0:00:23.692
right around spring break

0:00:23.692,0:00:25.302
and another found that men

0:00:25.302,0:00:26.262
produce the most

0:00:26.391,0:00:27.951
and the healthiest sperm

0:00:28.017,0:00:29.047
in early spring

0:00:29.291,0:00:31.501
what's causing this seasonal shift?

0:00:31.849,0:00:33.309
Scientists think our increase in

0:00:33.329,0:00:34.589
energy and better mood

0:00:34.589,0:00:36.659
have to do with changes in hormone levels

0:00:36.659,0:00:38.329
an important one is melatonin

0:00:38.389,0:00:40.709
sometimes called the "sleep hormone"

0:00:40.759,0:00:43.099
it's released at night and helps us to fall asleep

0:00:43.099,0:00:44.649
when the nights are longer

0:00:44.769,0:00:46.339
we produce more melatonin

0:00:46.883,0:00:48.963
and in spring, as the night gets shorter

0:00:49.094,0:00:50.344
we produce less of it

0:00:50.434,0:00:51.914
may be explaining why we feel

0:00:51.914,0:00:53.654
more awake and more active

0:00:53.693,0:00:55.313
seratonin is another chemical

0:00:55.403,0:00:56.613
that affects our mood

0:00:56.943,0:00:58.703
it's known as the "happiness hormone"

0:00:58.703,0:01:00.453
and it's level risens in spring time

0:01:00.453,0:01:01.583
as it gets sunnier

0:01:01.739,0:01:03.459
and the pathologists think that

0:01:03.459,0:01:04.649
this changes in hormone levels

0:01:04.649,0:01:06.449
may have to do with survival and

0:01:06.490,0:01:07.300
reproduction

0:01:07.320,0:01:09.110
many animals lay low in the winter

0:01:09.110,0:01:11.200
using less energy because food is sacarce

0:01:11.200,0:01:13.000
early humans might have done the same

0:01:13.040,0:01:15.660
when food became more abundant in the spring

0:01:16.167,0:01:18.157
and it make sense that they become...

0:01:18.195,0:01:18.875
more....

0:01:19.465,0:01:20.065
active

0:01:20.295,0:01:21.155
not surprisingly

0:01:21.155,0:01:22.905
as you move toward the equator

0:01:22.905,0:01:24.255
spring fever disappears

0:01:24.458,0:01:25.238
for example

0:01:25.439,0:01:27.739
scientists have noticed that seasonal changes

0:01:27.759,0:01:29.489
and the birth rates of field mice

0:01:29.489,0:01:30.269
flatten out

0:01:30.474,0:01:32.264
as you get closer to the equator

0:01:32.264,0:01:34.014
but sunshine may not be the only

0:01:34.014,0:01:35.454
spring time "pick me up"

0:01:35.601,0:01:37.561
for humans, the optimal temperature for

0:01:37.561,0:01:39.547
good mood is 72 degrees Fahrenheit

0:01:40.207,0:01:41.403
and let's face it

0:01:41.533,0:01:43.520
once the temperature starts to rise

0:01:44.173,0:01:45.533
we're wearing a lot less

0:01:45.533,0:01:47.923
for Scientific Americans and Instant Egghead

0:01:48.085,0:01:49.515
I'm Yasmin Tayag