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Did humans lose a sixth sense?

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  • Jeroen Kumeling
    Did humans lose a sixth sense? Sensory nerve cells from the vomeronasal organ By BBC News Online Science Editor Dr David Whitehouse Our distant ancestors may
    Message 1 of 1 , Dec 16, 1999
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      Did humans lose a sixth sense?


      Sensory nerve cells from the vomeronasal organ


      By BBC News Online Science Editor Dr David Whitehouse

      Our distant ancestors may have had a sixth sense that modern humans have
      lost because of a genetic mutation.

      Some researchers believe that the vestige of an organ that we all have in
      our noses was once responsible for detecting chemical signals given off by
      other humans. Some even think that it still influences our behaviour.

      Located just behind our nostrils are two tiny pits called the vomeronasal
      organ (VNO). The organ contains nerves that respond to chemicals called
      pheromones that are secreted by many animals. Whether humans do so as well
      is a matter of conjecture.

      In many creatures, pheromones trigger a variety of instinctive behaviours
      such as aggression and mating.

      Mouse gene

      Professor Catherine Dulac of the Harvard Medical School and researchers have
      isolated in mice a gene that she believes plays a major role in the
      detection of pheromones.



      Professor Dulac: Pheromones may play an as yet unappreciated role in human
      behaviour

      Humans have the gene as well but in a mutated form that may make it useless
      for detecting pheromones. This suggests we may once have had the ability to
      pick up the delicate chemical language of pheromones but have now lost it
      because the VNO cannot develop and function properly.

      The researchers are currently making a careful search for other human genes
      that we may use to detect pheromones other than the one we share with mice.
      Rats and mice have well-developed VNO's containing millions of nerve cells.
      The human VNO is different - it may work in the same way or it may not.

      Pheromones from insects and rodents are known but so far nobody has been
      able to find one from humans, despite the scent products that can be bought
      with names like Desire.

      Menstrual cycles

      There is some evidence that pheromones are at work in humans. Some research
      suggests that the female menstrual cycle can be advanced or retarded by
      sniffing the scent from other females captured via underarm pads. However,
      some scientists believe that the VNO is not responsible for detecting these
      scents. Instead, they are picked up by the so-called main olfactory system
      which runs our general sense of smell.



      Frogs are stimulated by pheromones

      Some scientists have speculated that the signals from the main olfactory
      system, situated further up the nose than the VNO, go to higher regions of
      the brain where scents can be associated with memories. Signals from the
      VNO, however, if it works, may be routed directly into brain regions
      responsible for more unconscious and instinctive behaviour.

      The team at the Harvard Medical School and the Massachusetts General
      Hospital have isolated a molecule, called TRP2, that acts as a trigger for
      pheromone reception on the VNO. It works in mice and rats but apparently
      humans do not have either the same molecule or the nerve connections found
      in rodent that are sensitive to pheromones.

      Professor Dulac believes that talk of a sixth sense is nonsense but that
      pheromones may play an as yet unappreciated role in human behaviour.
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