The Evolutionary Paradox of Our Sense of Smell
Dr. Stuart Firestein is the Chair of Columbia University's Department of Biological Sciences. His colleagues and he study the vertebrate olfactory receptor neuron as a model for investigating general principles and mechanisms of "signal transduction" — the ways in which chemicals, such as neurotransmitters, hormones, and peptides with membrane receptors, exert their influence in the brain and nervous system. He hypothesizes that the olfactory neuron is uniquely suited for these studies since it is designed specifically for the detection and discrimination of a wide variety of small organic molecules, i.e. odors.
Question: Is olfaction a more primitive or sophisticated sense?
Stuart Firestein: So olfaction is quite a remarkable sense actually. It’s often called the most primitive sense, the ability to detect chemicals in the environment and of course in biology the word primitive has a kind of a funny connotation. On the one hand you might say primitive meaning well the simplest or the most rudimentary, which is the typical meaning of the word primitive. But in biology of course because things happen over evolutionary time the more primitive something is the longer it has had to evolve and become "better," if you will, more perfected if you will. And so this idea that the olfactory sense is the most primitive may also make it in some ways that most sophisticated.
Question: How does olfaction work on a neurological level?
Stuart Firestein: The olfactory sense works by having this thin tissue lining the region of your nose way up at the top with a set of cells which are called olfactory sensory neurons. The important thing there is they are true neurons, that is brain cells. They’re like the cells in your brain inside your skull, but they’ve kind of been pushed out into the top of your nose where they have the ability now to come into contact with odors in the environment or odors in food as I just mentioned to you.
These cells have the remarkable ability to detect and discriminate among a tremendous variety and number of chemical compounds out there in the world, which we call odors. There are at least 10,000, maybe 100,000 of them. There is certainly 10,000 identified odors because this is what we can find in the catalogs of flavor and fragrance companies and these are mostly only the good odors. There is probably another 10,000 bad-smelling odors as well and then many new odors are created every day.
Most odors are small molecules. They’re what we call organic molecules in that they’re made up of carbon, but they’re relatively small. They’re volatile. They float around the air and they come up into your nose and can be trapped on the surface of these specialized neurons, olfactory sensory neurons, trapped by receptors that are on the surface of these cells. These receptors can be thought of as a kind of a lock-and-key mechanism, at least to a first approximation. If you imagine that the receptor is a lock then a key is the odor molecule and if the odor molecule has the right shape, it fits into the lock and activates the cell. It tells the cell "I’ve found something that fits my receptor and I’ll change my electrical qualities and signal the brain that I’ve found a molecule that fits." On the other hand, you might have another receptor shaped like this and this molecule won’t fit in it, but this molecule fits nicely. And so we’re able to discriminate between different odors based on their shape and other chemical properties that make them either bind to or not bind to, fit or not fit into one of these receptors or locks. What's remarkable about the olfactory system is the number of locks that we make, the number of receptors.
So in a mouse or a rodent or a dog there are nearly a thousand different types of these proteins, of these receptors on the surface of all these cells, these millions of cells in your nose. Each one of those protein receptors, each one of those locks if you will, is encoded by a gene in your genome. Even in humans we have fewer receptors, but we still have quite a large number, about 450 of them.
So let me put that in a little bit of perspective: we have about 25,000 genes that make up our whole genome. The whole plan for what we are is 25,000 genes in our genome, so that means... and that is typical of most mammals. A mouse or a rat is about the same. So in humans that means that nearly 2% of the genes in our genome are devoted to our sense of smell, devoted to making these receptors. That is about 1 out of every 50 genes. In a mouse or a rat it’s almost 5% or about 1 out of every 30 genes devoted to making receptors in your nose. So clearly there is an evolutionary commitment to the sense of smell, if you will.
Recorded September 22, 2010
Interviewed by Andrew Dermont
Olfaction may be both the most primitive and the most sophisticated of our five senses.
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A trio of intriguing galaxy clusters<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yNDQzNDA0OS9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYxNTkzNzUyOH0.0IRzkzvKsmPEHV-v1dqM1JIPhgE2W-UHx0COuB0qQnA/img.jpg?width=980" id="d69be" class="rm-shortcode" data-rm-shortcode-id="2d2664d9174369e0a06540cb3a3a9079" data-rm-shortcode-name="rebelmouse-image" />
The three galaxy clusters imaged for the study
Mapping dark matter<span style="display:block;position:relative;padding-top:56.25%;" class="rm-shortcode" data-rm-shortcode-id="d904b585c806752f261e1215014691a6"><iframe type="lazy-iframe" data-runner-src="https://www.youtube.com/embed/fO0jO_a9uLA?rel=0" width="100%" height="auto" frameborder="0" scrolling="no" style="position:absolute;top:0;left:0;width:100%;height:100%;"></iframe></span><p>The assumption has been that the greater the lensing effect, the higher the concentration of dark matter.</p><p>As scientists analyzed the clusters' large-scale lensing — the massive arc and elongation visual effects produced by dark matter — they noticed areas of smaller-scale lensing within that larger distortion. The scientists interpret these as concentrations of dark matter within individual galaxies inside the clusters.</p><p>The researchers used spectrographic data from the VLT to determine the mass of these smaller lenses. <a href="https://www.oas.inaf.it/en/user/pietro.bergamini/" target="_blank" rel="noopener noreferrer">Pietro Bergamini</a> of the INAF-Observatory of Astrophysics and Space Science in Bologna, Italy explains, "The speed of the stars gave us an estimate of each individual galaxy's mass, including the amount of dark matter." The leader of the spectrographic aspect of the study was <a href="http://docente.unife.it/docenti-en/piero.rosati1/curriculum?set_language=en" target="_blank">Piero Rosati</a> of the Università degli Studi di Ferrara, Italy who recalls, "the data from Hubble and the VLT provided excellent synergy. We were able to associate the galaxies with each cluster and estimate their distances." </p><p>This work allowed the team to develop a thoroughly calibrated, high-resolution map of dark matter concentrations throughout the three clusters.</p>
But the models say...<p>However, when the researchers compared their map to the concentrations of dark matter computer models predicted for galaxies bearing the same general characteristics, something was <em>way</em> off. Some small-scale areas of the map had 10 times the amount of lensing — and presumably 10 times the amount of dark matter — than the model predicted.</p><p>"The results of these analyses further demonstrate how observations and numerical simulations go hand in hand," notes one team member, <a href="https://nena12276.wixsite.com/elenarasia" target="_blank">Elena Rasia</a> of the INAF-Astronomical Observatory of Trieste, Italy. Another, <a href="http://adlibitum.oats.inaf.it/borgani/" target="_blank" rel="noopener noreferrer">Stefano Borgani</a> of the Università degli Studi di Trieste, Italy, adds that "with advanced cosmological simulations, we can match the quality of observations analyzed in our paper, permitting detailed comparisons like never before."</p><p>"We have done a lot of testing of the data in this study," Meneghetti says, "and we are sure that this mismatch indicates that some physical ingredient is missing either from the simulations or from our understanding of the nature of dark matter." <a href="https://physics.yale.edu/people/priyamvada-natarajan" target="_blank">Priyamvada Natarajan</a> of Yale University in Connecticut agrees: "There's a feature of the real Universe that we are simply not capturing in our current theoretical models."</p><p>Given that any theory in science lasts only until a better one comes along, Natarajan views the discrepancy as an opportunity, saying, "this could signal a gap in our current understanding of the nature of dark matter and its properties, as these exquisite data have permitted us to probe the detailed distribution of dark matter on the smallest scales."</p><p>At this point, it's unclear exactly what the conflict signifies. Do these smaller areas have unexpectedly high concentrations of dark matter? Or can dark matter, under certain currently unknown conditions, produce a tenfold increase in lensing beyond what we've been expecting, breaking the assumption that more lensing means more dark matter?</p><p>Obviously, the scientific community has barely begun to understand this mystery.</p>
Astronomers spot an object heading into Earth orbit.
Minimoons<p>Scientists have confirmed just two prior minimoons. One was <a href="https://en.wikipedia.org/wiki/2006_RH120" target="_blank">2006 RH120</a>, which orbited us from September 2006 to June 2007. The other was <a href="https://en.wikipedia.org/wiki/2020_CD3" target="_blank">2020 CD3</a>, which got stuck in the 2015–2016 timeframe, and is believed to gotten away in May 2020.</p><p>2020 SO, the new kid on the block, is expected to arrive in October 2020 and pop out of orbit in May 2021.</p><div id="37962" class="rm-shortcode" data-rm-shortcode-id="f4c0fc8a2cba6536ea4cd960ebed3e6e"><blockquote class="twitter-tweet twitter-custom-tweet" data-twitter-tweet-id="1307729521869611008" data-partner="rebelmouse"><div style="margin:1em 0">Asteroid 2020 SO may get captured by Earth from Oct 2020 - May 2021. Current nominal trajectory shows shows capture… https://t.co/F5utxRvN6Z</div> — Tony Dunn (@Tony Dunn)<a href="https://twitter.com/tony873004/statuses/1307729521869611008">1600621989.0</a></blockquote></div>
Identifying 2020 SO<p>The first clue 2020 SO isn't your ordinary asteroid is its exceptionally low velocity. It's traveling much more slowly that a typical asteroid — their <a href="https://www.lpi.usra.edu/exploration/training/illustrations/craterMechanics/" target="_blank">average rate of travel</a> <a href="https://www.lpi.usra.edu/exploration/training/illustrations/craterMechanics/" target="_blank" rel="noopener noreferrer"></a>is 18 kilometers (58,000 feet) per second. Even <a href="https://en.wikipedia.org/wiki/Moon_rock" target="_blank">moon rocks</a> sent careening into Earth orbit by impacts on the lunar surface outpace pokey 2020 SO.</p><p>For another thing, 2020 SO has an orbital path very similar to Earth's, lasting about one Earth year. It's also just slightly less circular than our own orbit, from which it's barely tilted off-axis.</p><p>So, what is it? <a href="https://cneos.jpl.nasa.gov/ca/" target="_blank">NASA estimates</a> that the object has dimensions very reminiscent of a discarded Centaur rocket stage from the <a href="https://en.wikipedia.org/wiki/Surveyor_2" target="_blank" rel="noopener noreferrer">Surveyor 2 mission</a> that landed an unmanned craft on the moon. Back in the day, rocket stages were jettisoned as craft were aimed toward their desired position. This stuff, if released high enough, remains in space. It appears that this Centaur rocket, launched in September 1966, is now making its way back homeward, at least for a little bit.</p><p>When 2020 SO arrives at its closest point in December, the rocket is expected to be about 50,000 kilometers from Earth. Its next closest approach is much further: 220,000 kilometers, in February 2010.</p><img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yNDQzMDk3NC9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYyODg1MTQ1MX0.HGknDwqp0GmeuczKY_AS7vrPG7KMFUc_XO95tNoI2xo/img.jpg?width=980" id="e5cda" class="rm-shortcode" data-rm-shortcode-id="85eb1f790d8c3ee5b261f7ba13eaa5e1" data-rm-shortcode-name="rebelmouse-image" alt="Centaur rocket stage" />
Centaur rocket stage
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