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A common misunderstanding –even made by some experts– is that a species evolves, or worse, an individual creature evolves. Strictly speaking individuals do not evolve. They can however leave many offspring with variable traits that differ from their parents and from one another.
Now this inherent variability of sexually reproducing populations is a key ingredient in how members of the same species may, over time, differ from their ancestors. It is the variability when combined with sexual selection and genetic drift that explains the shifts we see among the offspring from several generations. Here is where a poorly expressed idea that species evolve over time comes from; the tendency of offspring to resemble, but not actually possess precisely the same inheritance as their parents.
Over subsequent generations slight changes in the variability of chromosomes and the expression of traits on those chromosomes will cause organisms to pass on a different set of variable traits to their children from the one's that they inherited from their parents.
Because not all members of a breeding population will contribute reproductively to the next generation some variability is lost. But equally important is the fact that these contributions from reproductively successful creatures really vary so that shifts over time in the surviving population may lead to diverging traits. These differences make traits so variable from ancestral traits that people mistakenly say a "species evolved" over time.
That idea is a mistake. Accurately stated: populations vary, breeding populations comprise a species, but species do not evolve–that is change themselves over time. Even the discoverer of natural selection Alfred Russell Wallace mistakenly believed that plants and animals change in ways to "perfectly fit their new environments." The error is in confusing future potentiality with past performance and then attributing to breeding members of a population a characteristic behavior they do not actually possess. What a breeder does possess is a variability in the chromosomes that may be or may not be of value to an offspring. When conditions change those traits that were selected for may or may not adapt a creature to the shifting situation.
Instead, as selection pressures increase when conditions change different variations survive in a population. Some variations are beneficial, others are not, some are just neutral. Because not all variations are bred–and thus passed along–into the next generation, a discernible difference emerges over time in the progeny populations.
The most that can be said is that many offspring don't survive to pass on their varied traits, those that do survive to reproduce create a slightly different population.
That population has a different mix of genetic characteristics than the preceding contributing generation, so change is ever so slightly shifted from one generation to the next. When isolated for any long period of time populations may diverge more obviously in shape and behavior -- but they do not really "evolve."
Mistaken notions of Darwinism in the popular mind.
New ways to think about the natural world.
The world is not the product of freely chosen paths from a host of opportunities, as some argue.
The reason that variation and thus freedom of choice is circumscribed is because those creatures that existed before us influence and constrict what can occur. Which is to say that within the further confines of chemical and physical restraints, one generation is dependent on what it inherited and finds useful from the prvious generation.
Within these confines there is wide variability, but that variation is not inexhaustible. Then there exists an unpredictable range of opportunities created by surroundings and other creatures that is called a milieu and in that setting there exists contingent probability for one breeding population to survive. Not all breeding polutaions survive, so that the outcome is contingent on both physical changes in the surroundings and capabilities of the survivors to adapt and adapt well beyond the capability of their competitors.
Contingent meaning a future condition that is not with any certainty likely based on current situations.
Populations and population-based concepts
Populations vary because individuals in those populations have different chromosomes inherited from many different ancestors.
population thinking correctly replaces typological thought
The world is not understood in terms of abstract groups of things, instead it is the outcome of the reproductive capacities and fertile potential of the preceding generations.
Since Plato and Aristotle typological thought --or thinking according to type--has dominated the natural sciences in which beings are separated into classes of things based on apparent similarities and contradistinctions. Instead descent places all creatures into lineages based on descent from common parents or the fact that beings have a similar ancestry.
Things in this world are not capable of being exactly meshed with other other creatures of the conditions of their existence, instead they approximate functions that meet their own and one another's needs.
The restraints mentioned above are not factors that predict the outcome of the future -- instead they are limitations dictated by the physical , chemical and biological features of the material universe.
Things descend from a common ancestor from which these parents the many offspring vary enormously. They do not evolve, they do not will themselves to be for or less fit. The variability among different surviving offspring leads to subtle and even abrupt changes in the subsequent generations. Thus creatures descend sharing common origins and possessing the same basic but variable traits.
Since Darwin did not, as Newton had done, evoke God as the origin of the laws of variability and chance the matter arose of where morality in such a world where fortune or luck appears to replace progress and perfectibility orinates. Many found and still find Darwin's replacement of God's special creation with natural selection an offensive idea because it challenged the notion of non-situational ethics with situational morality, or worse no moral system at all to guide humans and separate human creatures from the animals driven by instincts.
Joseph Siry, written discourses
Analyses can be found in the following pages: