<story><title>Plants repeatedly got rid of their ability to obtain their own nitrogen</title><url>https://arstechnica.com/science/2018/05/plants-repeatedly-got-rid-of-their-ability-to-obtain-their-own-nitrogen/</url></story><parent_chain><item><author>chiefalchemist</author><text>&amp;gt; &amp;quot;Use it or lose it&amp;quot; applies to genes as much as (or maybe even more than) anything else. Genes involved in biological processes are lost if the trait they confer is unused or unnecessary.&amp;quot;&lt;p&gt;Why would this be true? Can&amp;#x27;t a gene be dormant? Or perhaps over-ridden but another gene or genes?&lt;p&gt;Or is, over the long haul (read: __many__) years any and all genes will naturally mutate (that is, be lost). Then if the &amp;quot;replacement&amp;quot; is more advantageous, the replacement will persist.&lt;p&gt;Fair enough. But that&amp;#x27;s not use it &amp;#x2F; lose it per se. It&amp;#x27;s still in use, but less so (and is over time replaced).</text></item></parent_chain><comment><author>azernik</author><text>It&amp;#x27;s that second one. Geneticists talk about genes being &amp;quot;conserved&amp;quot; when they are needed, and use the level of conservation to understand how essential a gene is to the functioning of an organism. For example, hemoglobin genes are &lt;i&gt;highly&lt;/i&gt; conserved across all animals, because any mutation there is likely to produce an unviable organism.&lt;p&gt;If something is &lt;i&gt;not&lt;/i&gt; conserved by selection, then the default is for it to be overwritten. So more like &amp;quot;need it or lose it&amp;quot;. But I feel like that&amp;#x27;s pretty close to the article&amp;#x27;s phrasing.</text></comment>
<story><title>Plants repeatedly got rid of their ability to obtain their own nitrogen</title><url>https://arstechnica.com/science/2018/05/plants-repeatedly-got-rid-of-their-ability-to-obtain-their-own-nitrogen/</url></story><parent_chain><item><author>chiefalchemist</author><text>&amp;gt; &amp;quot;Use it or lose it&amp;quot; applies to genes as much as (or maybe even more than) anything else. Genes involved in biological processes are lost if the trait they confer is unused or unnecessary.&amp;quot;&lt;p&gt;Why would this be true? Can&amp;#x27;t a gene be dormant? Or perhaps over-ridden but another gene or genes?&lt;p&gt;Or is, over the long haul (read: __many__) years any and all genes will naturally mutate (that is, be lost). Then if the &amp;quot;replacement&amp;quot; is more advantageous, the replacement will persist.&lt;p&gt;Fair enough. But that&amp;#x27;s not use it &amp;#x2F; lose it per se. It&amp;#x27;s still in use, but less so (and is over time replaced).</text></item></parent_chain><comment><author>samatman</author><text>It&amp;#x27;s simpler than this: If you can obtain a nutrient from the environment, then the machinery to make it yourself breaking won&amp;#x27;t kill you.&lt;p&gt;Same way mammals keep losing vitamin C synthesis when they settle on a diet that&amp;#x27;s rich in it.&lt;p&gt;This isn&amp;#x27;t &amp;quot;use it or lose it&amp;quot; this is just &amp;quot;lose it and don&amp;#x27;t die&amp;quot;. Having the synth path is better, dying is worse.</text></comment>