The Mechanics Of Evolution

The Mechanics of Evolution Interaction of Natural Selection and Inheritance (Genetics)

Lifeforms are not immutable; they change.

Natural Selection and how it works

The basics are pretty simple:

In each species, there is variation in traits. For example, some beetles are green and some are brown.

There is differential reproduction. Since the environment can't support unlimited population growth, not all individuals get to reproduce to their full potential. In this example, green beetles tend to get eaten by birds and survive to reproduce less often than brown beetles do.

There is heredity. The surviving brown beetles have brown baby beetles because this trait has a genetic basis.

End result: The more advantageous trait, brown coloration, which allows the beetle to have more offspring, becomes more common in the population. If this process continues, eventually, all individuals in the population will be brown.

If you have variation, differential reproduction, and heredity, you will have evolution by natural selection as an outcome. It’s as simple as that.

We can make it more complicated.

... the outward physical manifestation of internally coded, inheritable, information.

That is, it is comprised of both a phenotype and a genotype.

The "outward, physical manifestation" of the organism The physical parts, the sum of the atoms, molecules, macromolecules, cells, structures, metabolism, energy utilization, tissues, organs, reflexes and behaviors. Anything that is part of the observable structure, function or behavior of a living organism.

This is the "internally coded, inheritable information" carried by all living organisms. This stored information is used as a "blueprint" or set of instructions for building and maintaining a living creature. These instructions are found within almost all cells (the "internal" part), they are written in a coded language (the genetic code), they are copied at the time of cell division or reproduction and are passed from one generation to the next ("inheritable"). These instructions are intimately involved with all aspects of the life of a cell or an organism. They control everything from the formation of protein macromolecules, to the regulation of metabolism and synthesis.

The relationship between the two is simple! The

codes for the

We can make it more complicated. Fitness describes how good a particular genotype is at leaving offspring in the next generation relative to how good other genotypes are at it. So if brown beetles consistently leave more offspring than green beetles because of their color, you'd say that the brown beetles had a higher fitness.

Fitness is a relative thing. A genotype's fitness depends on the environment in which the organism lives.

The Fitness Concept Fitness is a handy concept because it lumps everything that matters to natural selection (survival, mate-finding, reproduction) into one idea. The fittest individual is not necessarily the strongest, fastest, or biggest. A genotype's fitness includes its ability to survive, find a mate, produce offspring — and ultimately leave its genes in the next generation.

An adaptation is a feature that is common in a population because it provides some improved function. Adaptations are well fitted to their function and are produced by natural selection. Adaptations can take many forms: a behavior that allows better evasion of predators, a protein that functions better at body temperature, or an anatomical feature that allows the organism to access a valuable new resource — all of these might be adaptations. Many of the things that impress us most in nature are thought to be adaptations.

Adaptation

Microevolution and its processes Microevolution is evolution on a small scale — within a single population. That means narrowing our focus to one branch of the tree of life.

Mutation Some "green genes" randomly mutated to "brown genes" (although since any particular mutation is rare, this process alone cannot account for a big change in allele frequency over one generation).

Migration (or gene flow) Some beetles with brown genes immigrated from another population, or some beetles carrying green genes emigrated.

Genetic drift When the beetles reproduced, just by random luck more brown genes than green genes ended up in the offspring. In the diagram at right, brown genes occur slightly more frequently in the offspring (29%) than in the parent generation (25%).

Natural selection Beetles with brown genes escaped predation and survived to reproduce more frequently than beetles with green genes, so that more brown genes got into the next generation.

Macroevolution and its processes Macroevolution is evolution on a grand scale — what we see when we look at the over-arching history of life: stability, change, lineages arising, and extinction.

Macroevolution generally refers to evolution above the species level. So instead of focusing on an individual beetle species, a macroevolutionary lens might require that we zoom out on the tree of life, to assess the diversity of the entire beetle clade and its position on the tree.

Natural Selection: A Summary 1. 2. 3. 4. 5. 6. 7. 8.

All species produce offspring at a faster rate than food supplies can increase. Except for identical twins, no two individuals are exactly alike. In each generation, more individuals are produced than can survive. Individuals that possess certain traits have an advantage over those that do not. The environment determines whether a trait is beneficial. Traits are inherited and passed on to the next generation. Over time, successful variations accumulate in a population, and a new species may appear. Geographical isolation may lead to the formation of a new species.

Mechanism of Evolutionary Change by Natural Selection 1. 2. 3.

A trait must be inherited in order to have importance in natural selection. Natural selection cannot occur without variation in inherited characteristics. Fitness is a relative measure that will change as the environment changes.