Download Chapter 22 Species and Their Formation

Chapter 22
Species and Their Formation
Biology 101
Tri-County Technical College
Pendleton, SC
Biological Species
 Species are independent evolutionary units
 Used to use morphological concept to assign
organisms to a species (Linnaeus)
 Biological species concept introduced by Ernst
Mayr in 1940
 Species are groups of actually or potentially
interbreeding natural populations which are
reproductively isolated from other such groups
Species, cont.
 “Actually and potentially” assert that, even if some
members of species are NOT in the same place (at
same time) and hence unable to mate, they should
NOT be placed in separate species if they are like to
mate if they were together
 “Natural” is important because only in nature does
exchange of genes affect evolutionary processes
Species, cont.
 Interbreeding of two different species in
captivity does NOT affect evolution
 Gene exchange is MAIN REASON why
species are cohesive units
 Are some limitations to biological species
concept

Speciation often very gradual process
Species, cont.
 If barrier divides one population into two,
the daughter population may evolve
independently long before they become
reproductively incompatible
 May also become reproductively
incompatible before they evolve any
noticeable morphological differences
 Short chapter, there is no Student Self
Assessment in any form for this chapter