It looks, once again, like it is time to remind people that the terminology used to discuss evolution has definitions that are relevant to the context of the discussion. Personal and secret definitions of technical terminology confuse and obfuscate discussion. Most of us try and maintain openness and consistency in how we use these terms so that we can communicate effectively and get our points across to others.
Using accepted and widely used terminology properly is a rational thing to do in order to maintain the quality of the discussion and the debate.
I'll start with these often misused terms to set the pace. I'm sourcing Wikipedia for some since the information on there is valid, up to date, easily accessible, well-referenced and reasonably clear to layman as well as experts.
Genetic bottleneck.
A population bottleneck or genetic bottleneck is a sharp reduction in the size of a population due to environmental events such as famines, earthquakes, floods, fires, disease, and droughts; or human activities such as specicide, widespread violence or intentional culling, and human population planning.
Population bottleneck - Wikipedia
Since this describes a reduction in population number and genetic variation, it in no way resembles selection used in artificial breeding. A breeder selects traits that are useful to people and tries to propagate those traits into the population. A breeder of border collies does not try to decimate the border collie population in order propagate some new trait they have discovered. The genetic variation and population size of border collies is not reduced. In fact, variation is increased due to the introgression of the new trait and underlying genetics.
A genetic bottleneck is not a speciation event. The species remains the same prior to and just after the bottleneck event.
Adaptation.
Adaptation is an term used to describe several conditions of which only one condition is the adaptation of evolution.
Here I will reference the work of John Maynard Smith in his book describing the theory of evolution.
Physiological versatility is adaptation where rapid physiological adjustment allows an organism to avoid predation by altering its appearance or maintain it's internal environment under stress. Flat fish changing color or me shivering in the cold or sweating in the hot sun are examples. There is no change in my genetics causing or resulting from the adjusted physiology.
The second condition also often referred to as adaptation is developmentally flexible. Gradual changes in structure that better allow an organism to survive in a new environment. Growing calluses on the hands from continuous manual labor that protects the hands from wearing injury is an example. The individual undergoing this change does not have a concomitant alteration of their genes resulting in the altered structure.
The final definition of adaptation is a change in the genes that can proliferate or fix in a population over time under the protection of some relevant selection.
Straight from Maynard Smith. "An animal or plant is genetically adapted to particular conditions if it possesses characters suiting it for life in those conditions, and if it develops those characters in all or most environments in which it is able to develop at all."
An animal that evolves a trait for increased heat tolerance will maintain that trait even if it is placed in a colder environment for instance.
Evolution is not wished away into a cornfield by semantic word games replacing evolution with adaptation. Genetic adaptation is evolution.
Due to the common use of adaptation and that it can describe different conditions it is often a source of confusion for those untrained in biological science. That ambiguity has, as well, been exploited by those intent on using it as a means of misinformation regarding what evolution is.
Maynard Smith, John. 1993. The Theory of Evolution (Canto) 3rd Edition. Pages 32-34.
Biological fitness.
Fitness (often denoted w or ω in population genetics models) is the quantitative representation of individual reproductive success. It is also equal to the
average contribution to the
gene pool of the next generation, made by the same individuals of the specified genotype or phenotype.
Fitness (biology) - Wikipedia
It is not how athletic or weak an individual is. Nor does it denote cultural issues of wealth or poverty. Nor moral position or judgement.
It is a determination of how traits under given selection enable a net increase in reproductive success of members of a population. If, in a warm environment, those members of the population have genes that provide them with greater heat tolerance, they will reproduce with greater success than those members of the population without those genes. It is not to say that those members without the heat tolerance genes won't reproduce, just that on average under the selection of that aspect of climate, they will reproduce less. Under continued selection, the population will gradually evolve to those members with the genes for greater heat tolerance.
Move that population to a colder climate and the selection shifts it in favor of those with genetics to tolerate the cold.
All individuals are not equally fit. This is a claim without the support of evidence or experiment.
Natural selection.
The modern, and more fitting an proper, term describing the environment as it acts on the various genotypes and phenotypes found in a population.
Natural selection does not mean that the beautiful and strong will survive and the weak and ugly will not. It means that those with traits suiting them for survival in a given environment will have greater fitness for that environment and reproduce more successfully on average.
"Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations."
Natural selection - Wikipedia
Here is one experiment among many that demonstrate natural selection in a wild population.
Barrett, R.D.H., S. Laurent, R. Mallarino, S.P. Pfeifer, C.C.Y. Xu, M. Foll, K. Wakamatsu, J.S. Duke-Cohan, J.D. Jensen & HE. Hoekstra. 2019. Linking a mutation to survival in wild mice.
Science. 363(6426): 499-504.
https://hoekstra.oeb.harvard.edu/files/hoekstra/files/barrett2019sci.pdf
The environment under discussion is the total environment experienced by members of a population and includes the internal and external as well as the biotic an abiotic aspects. It is not simply the weather.
There is no evidence supporting change in a population is under the direction of the population. This has not been supported by the small body of work to that end and has been refuted by more recent work showing that directed change is actually mis-identified natural selection.
Maisnier-Patin, S. & J.R. Roth. 2015. The origin of mutants under selection: how natural selection mimics mutagenesis (adaptive mutation). Cold Spring Harbor perspectives in biology, 7(7), a018176.
https://cshperspectives.cshlp.org/content/7/7/a018176.full.pdf
At some point I would like to further discuss how making up taxonomy and randomly renaming a species just cause is not science and is only self-serving nonsense that doesn't enhance discussion.
