How Evolution Happens

Evolution has occurred

"There is grandeur in this view of life, with its several powers, having been originally breathed by the Creator into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being evolved." -  The final sentence of "The Origin of Species" by Charles Darwin 1859.

Modern biogeography is based on the knowledge that evolution has occurred.

The process of evolution is "selection" and its observable product is speciation.

The Basic Concepts and Terms

A  group of organisms that have begotten each other as ancestor and descendant (either as individuals or as a group) along a continuum of time are called a LINEAGE.
A lineage that is made up of an ancestor and ALL of its descendants is called a CLADE.
Clados is latin for branch.
When a new branch forms in PHYLOGENY the process is called CLADOGENESIS
A PHYLOGENY is the actual history of cladogenesis in a clade.
A CLADOGRAM is a schematic representation of the phylogeny.
 

Evolution operates at many scales.

Lineages can change over time or they can split.  Lineage splitting is cladogenesis, simple change over time without splitting is called ANAGENESIS.
The two processes are intertwined and often confused with each other.  When you look atthe phylogeny of a group, you are almost certainly observing both.
 

When Cladogenesis occurs at the appropriate scale, we call it SPECIATION.

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