(peaceful classical music)
(squeak)
- Why hello there Brain Stuff.
I wanted to talked to you
about one way that mice could
be considered more highly
evolved than humans.
Nipples!
Where as human males
develop a pair of nipples,
or sometimes more, that generally serve
no biological function.
Male mice exit the womb
with their bellies smooth
and nipple free.
So why do men have nipples?
Three or four weeks after conception
all human embryos develop
parallel mammary ridges
called milk lines.
They extend from the top of the chest
to the lower abdomen.
It's not until week seven or so
that genes in the
embryo's sex chromosomes,
you know usually XX or XY, kick in.
They're what cause a formation
of sexual dimorphism.
The physical traits that
distinguish biological males
from biological females.
But those genes don't tinker with
the already developing milk lines.
The milk lines naturally
recede as the fetus grows,
leaving behind nipples.
Now in mice, mammary tissue also forms
in both male and female embryos
during early pregnancy.
But according to Yale University research,
first published in 1999,
a particular protein
stops the process in male mice.
Just a few days after the mammary tissue
starts to form.
It produces a protein known
as parathyroid hormone-related peptide,
or PTHrP.
In male embryos, this protein signals
the mammary cells to
form hormone receptors
that attract the male hormones
already circulating in the embryo's blood.
Those hormones shut down
the mammary growth process
and degenerate what
tissue is already formed.
Leaving the dude rodents
nipple-less by birth.
Mice are among an elite group of mammals
with such efficient male
nipple destroying genes.
Horses and platypuses are in there too
and that sounds like a real fun party.
(thud)
Human males lacking anyway such system
are left with tissue that's even capable
of producing milk under
the right circumstances.
So, that's how men have nipples.
But, why?
Well, nipples and healthy
breast development
are closely linked with
female reproductive success.
So closely linked that
biologists figure it
was more evolutionarily advantageous
for all embryos to develop breast tissue
whether they'd wind up using it or not.
So ladies and gents, would
you breast feed a baby?
Let me know in the comments.
Actually, don't let me
know, I don't wanna know.
Learn lots more about male milk production
in my article Why do men have nipples?
on howstuffworks.com
Because apparently I'm pretty fascinated
with all things nipple related.
Again, another thing I shouldn't
have said on camera.
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