By Jean-Louis Santini
Washington (AFP) - The human nose can distinguish at least one trillion different odors,
millions more than previously estimated, US researchers said
Thursday.
For decades, scientists
accepted that humans could detect only 10,000 scents, putting the sense of smell well below
the capabilities of sight and hearing.
"Our analysis shows that the human capacity for discriminating smells is much larger than
anyone anticipated, said study co-author Leslie Vosshall, head of Rockefeller
University's Laboratory of Neurogenetics and Behavior.
The previous estimate for the nose's capabilities -- which are
carried out with the help of 400
olfactory receptors -- dated to the 1920s and was not
backed by data.
Researchers have estimated that the human eye and its mere three receptors can
distinguish several
million colors and that the ear
can discriminate 340,000
sounds.
"For smell,
nobody ever took the time to test," Vosshall said.
To conduct their research, scientists subjected 26 participants to mixtures made with 128
different odorant molecules that individually might evoke
grass, citrus or various chemicals, but were combined in groupings of up to 30.
"We didn't want them to be explicitly recognizable, so most
of our mixtures were pretty
nasty and weird," Vosshall said.
"We wanted people to pay attention to 'here's this really complex thing
– can I pick another complex thing as being different?'"
Volunteers would sample
three vials of scents at a time -- two that were the same
and one that was different -- to see if they could detect which was the
outlier, completing 264 such comparisons.
Although volunteers'
abilities varied greatly, they could on average discern the
difference between vials with up to 51 percent of the same components, with
fewer volunteers detecting a difference once the mixtures shared more
components.
Researchers then extrapolated
how many odors the average person could detect if all
possible combinations of the 128 odorants were sampled, coming to their
estimate of at least one trillion.
Lead researcher Andreas Keller, also of Rockefeller University,
said the number is almost
certainly too low given that there are numerous other odorants that can mix in
countless ways in the real world.
He said our
ancestors relied more on the sense of smell, but that refrigeration and
the development of
personal hygiene have limited odors in the modern world.
"This could explain our attitude that smell is unimportant, compared to hearing and
vision," Keller said.
He added that upright
posture, which raised humans' noses far from the ground where
odors often emanate, may also have contributed.
The sense of smell
is closely linked to human behavior and the researchers
stressed that studying it could shed light on how the human brain processes
complex information.
The study was published in the journal Science.
NOTE/FYI: I
don't believe it and as anyone who knows me can tell you, I am part dog.
Numbers too large; glib academic extrapolating trickery in search of additional
grant money. A gift to bloggers
nonetheless.
The Lodge: Smell
Of A Friend (Link)