Evolution descent with modification.
Descent can happen only when one group of organisms gives rise to another.
Evolution describes change in allele frequencies in populations over time.
When one generation of organisms reproduces and creates the next, the frequencies of the alleles for the various genes represented in the population may be different
from what they were in the parent generation.
Frequencies can change so much that certain alleles are lost or others become fixed—all individuals have the same allele for that character.
Over many generations, the species can change so much that it becomes quite different from the ancestral species, or a part of the population can branch off and become a new species (speciation).
Gene flow - the change in allele frequencies as genes from one population incorporates into another.
Mutation always random with respect to which genes are affected, although the changes in allele frequencies that occur as a result of the mutation may not be.
Random mating - organisms participate in intrasexual selection, which represent competitive interactions between the same sex (male-to-male or female-to-female) and intersexual selection, which represents the selection of reproductive partners of the opposite sex.
This leads to the evolution of secondary sexual characteristics for organisms to persuade members of the opposite sex.
The mutual evolution between two species, which is exemplified by predator– prey relationships.
The prey evolves in such a way that those remaining are able to escape predator attack.
Eventually, some of the predators survive that can overcome this evolutionary adaptation in the prey population. This goes back and forth, over and over.
Two unrelated species evolve in a way that makes them more similar.
They are both responding in the same way to some environmental challenge, and this brings them closer together.
We call two characters convergent characters if they are similar in two species, even though the species do not share a common ancestor.
Two related species evolve in a way that makes them less similar.
Divergent evolution can lead to speciation (allopatric or sympatric).
Similar evolutionary changes occurring in two species that can be related or unrelated.
They are simply responding in a similar manner to a similar environmental condition.
Species a group of interbreeding (or potentially interbreeding) organisms.
Speciation the process by which new species evolve.
Main forms of speciation:
Allopatric speciation - Interbreeding ceases because some sort of barrier separates a single population into two.
The two populations evolve independently, and if they change enough, then even if the barrier is removed, they cannot interbreed.
Sympatric speciation - Interbreeding ceases even though no physical barrier prevents it.
Other important terms:
Polyploidy - A condition in which an individual has more than the normal number of sets of chromosomes.
Although the individual may be healthy, it cannot reproduce with nonpolyploidic members of its species.
This is unusual, but in some plants, it has resulted in new species because polyploidic individuals are only able to mate with each other.
Balanced polymorphism - This condition can also lead to speciation if two variants diverge enough to no longer be able to interbreed (if, e.g., potential mates no longer recognize each other as possible partners).
Adaptive radiation - a rapid series of speciation events that occur when one or more ancestral species invades a new environment.
Traits are said to be homologous if they are similar because their host organisms arose from a common ancestor (which implies that they have evolved).
For example, the bone structure in bird wings is homologous in all bird species.
The study of embryos reveals remarkable similarities between organisms at the earliest stages of life, although as adults (or even at birth) the species look completely different.
Human embryos, for example, actually have gills for a short time during early development, hinting at our aquatic ancestry.
Darwin used embryology as an important piece of evidence for the process of evolution.
Most organisms carry characters that are no longer useful, although they once were.
Sometimes an environment changes so much that a trait is no longer needed, but is not deleterious enough to actually be selected against and eliminated.
Darwin used vestigial characters as evidence in his original formulation of the process of evolution, listing the human appendix as an example.
Fossil record—the physical manifestation of species that have gone extinct.