Natural selection
Darwin’s theory had two major tenets, one was that all living things (organisms) are related through common descent and the other was that natural selection was the main mechanism by which diversity in form and function among organisms although related, occurred.
" I am fully convinced that species are not immutable; but that those belonging to what are called the same genera are lineal descendants of some other and generally extinct species, in the same manner as the acknowledged varieties of any one species are the descendants of that species. Furthermore, I am convinced that Natural Selection has been the main but not exclusive means of modification.”
You can see the importance Darwin placed on this mechanism by noting that the extended title of the Origin of Species, includes this mechanism.
The Origin of species by Means of Natural Selection of The Preservation of Favoured Races in the Struggle for Life First edition. Charles Darwin. http://www.talkorigins.org/faqs/origin.html
Definition: Differential reproduction in response to some environmental pressure.
Look at classic presentation of concept.
Do you agree with the authors conclusion?
"If you have variation, differential reproduction, and heredity, you will have evolution by natural selection as an outcome. It is as simple as that."
Poll results:
I would like to see environmental pressure as part of the definition. Natural selection needs an "environment" that causes differential reproduction. It needs a story.
How would the "story" change if we started with more or less equal number of green and brown beetles on basically green shrubbery.
Why is natural selection not associated with survival in our working definition?
1. Obvious answer: If reproduction does not occur, even those that survive "best" do not pass their phenotype to the next generation, at least not via natural selection criteria.
2. Actually for Darwin, natural selection was survival of the fittest. This is because he saw sexual selection as something apart from natural selection.
Sexual selection, proposed by Darwin, The Descent of Man, and Selection in Relation to Sex.
"...My conviction of the power of sexual selection remains unshaken..." (C. Darwin, 1874, Preface) "We learn that the advantages which favored males derived from conquering other males in battle or courtship, and thus leaving a numerous progeny (male-male competition) are in the long run greater than those derived from rather more perfect adaptations to their conditions of life.We shall further see, and it could never have been anticipated, that the power to charm the female (female choice) has sometimes been more important than the power to conquer other males in battle" (Darwin, 1871, pg. 583)
Implies two major components to sexual selection, male-male competition and female choice.
Now sexual selection is considered a part of natural selection. But it remains one of most common instances in which selection for reproduction and survival may not be positively correlated. Males who fight or advertise via displays, may reproduce more than males that don't, but may actually not survive as long as those that don't.
Aside: Do sexual preferences with natural selection overtones exist in humans? https://pbsnc.pbslearningmedia.org/resource/tdc02.sci.life.evo.sweatytshirts/sweaty-t-shirts-and-human-mate-choice/
The non-trivia take home is the preference for potential "good genes" or in this instance the potential recombination of immune genes that could lead to more variability in young for resistance.