<p>Natural selection occurs because organisms with traits that help them survive and reproduce tend to have more offspring. In doing so, they will pass more copies of their inheritable traits on to the next generation. This process causes advantageous traits to become more common over time, while disadvantageous ones become rarer.<sup class="reference" id="_ref-Futuyma_0"><a title="" href="http://en.wikipedia.org/wiki/Evolution#_note-Futuyma"><font color="#0066cc">[1]</font></a></sup><sup class="reference" id="_ref-0"><a title="" href="http://en.wikipedia.org/wiki/Evolution#_note-0"><font color="#0066cc">[2]</font></a></sup><sup class="reference" id="_ref-1"><a title="" href="http://en.wikipedia.org/wiki/Evolution#_note-1"><font color="#0066cc">[3]</font></a></sup> Over many generations, this process can produce varied <a title="Adaptation" href="http://en.wikipedia.org/wiki/Adaptation"><font color="#0066cc">adaptations</font></a> to environmental conditions.<sup class="reference" id="_ref-understandingevolution_0"><a title="" href="http://en.wikipedia.org/wiki/Evolution#_note-understandingevolution"><font color="#0066cc">[4]</font></a></sup> As genetic differences in and between populations of a species accumulate, this <a title="Species" href="http://en.wikipedia.org/wiki/Species"><font color="#0066cc">species</font></a> may split into <a title="Speciation" href="http://en.wikipedia.org/wiki/Speciation"><font color="#0066cc">new species</font></a>. The similarities between organisms suggest that all known species are <a title="Common descent" href="http://en.wikipedia.org/wiki/Common_descent"><font color="#0066cc">descended from a single ancestral species</font></a> through this process of gradual divergence.<sup class="reference" id="_ref-Futuyma_1"><a title="" href="http://en.wikipedia.org/wiki/Evolution#_note-Futuyma"><font color="#0066cc">[1]</font></a></sup><sup class="reference" id="_ref-2"><a title="" href="http://en.wikipedia.org/wiki/Evolution#_note-2"><font color="#0066cc">[5]</font></a></sup><sup class="reference" id="_ref-3"><a title="" href="http://en.wikipedia.org/wiki/Evolution#_note-3"><font color="#0066cc">[6]</font></a></sup></p>

<p>The <a title="Theory" href="http://en.wikipedia.org/wiki/Theory"><font color="#0066cc">theory</font></a> of evolution by natural selection was first put forth in detail in <a title="Charles Darwin" href="http://en.wikipedia.org/wiki/Charles_Darwin"><font color="#0066cc">Charles Darwin</font></a>'s 1859 book <em><a title="The Origin of Species" href="http://en.wikipedia.org/wiki/The_Origin_of_Species"><font color="#0066cc">On the Origin of Species</font></a></em>. In the 1930s, Darwinian natural selection was combined with <a title="Gregor Mendel" href="http://en.wikipedia.org/wiki/Gregor_Mendel"><font color="#0066cc">Mendelian</font></a> <a title="Mendelian inheritance" href="http://en.wikipedia.org/wiki/Mendelian_inheritance"><font color="#0066cc">inheritance</font></a> to form the <a title="Modern evolutionary synthesis" href="http://en.wikipedia.org/wiki/Modern_evolutionary_synthesis"><font color="#0066cc">modern evolutionary synthesis</font></a>.<sup class="reference" id="_ref-understandingevolution_1"><a title="" href="http://en.wikipedia.org/wiki/Evolution#_note-understandingevolution"><font color="#0066cc">[4]</font></a></sup> With its enormous explanatory and <a title="Predictive power" href="http://en.wikipedia.org/wiki/Predictive_power"><font color="#0066cc">predictive power</font></a>, this theory has become the central organizing principle of modern biology, providing a unifying explanation for the <a title="Biodiversity" href="http://en.wikipedia.org/wiki/Biodiversity"><font color="#0066cc">diversity of life</font></a> on Earth.<sup class="reference" id="_ref-4"><a title="" href="http://en.wikipedia.org/wiki/Evolution#_note-4"><font color="#0066cc">[7]</font></a></sup><sup class="reference" id="_ref-5"><a title="" href="http://en.wikipedia.org/wiki/Evolution#_note-5"><font color="#0066cc">[8]</font></a></sup><sup class="reference" id="_ref-6"><a title="" href="http://en.wikipedia.org/wiki/Evolution#_note-6"><font color="#0066cc">[9]</font></a></sup></p>

<p><a id="History_of_evolutionary_thought" name="History_of_evolutionary_thought"></a></p>

<h2><span class="mw-headline">History of evolutionary thought</span></h2>

<li><a class="external text" title="http://www.rationalrevolution.net/articles/understanding_evolution.htm" rel="nofollow" href="http://www.rationalrevolution.net/articles/understanding_evolution.htm"><font color="#0066cc">Understanding Evolution: History, Theory, Evidence, and Implications</font></a> Deals heavily with the history of thoughts about evolution </li>

</ul>

</span>