EVOLUTION 1B

1 EJC H2 Biology T2W1 Evolution 1B Evolution 1B 1. Introduction What are species, exactly? Defining and recognising a species has been a controversial issue for a long time. There are many definitions for the concept of species. There is no universal species concept – one that applies to all organisms. Instead, scientists have been proposing dif ferent species concepts for years, and each is based on slightly different biological reasoning. Species concepts do not only define what a species is, but by defining what a species is, they also clarify what speciation is. 2. Learning Outcomes (h) Explain t he various concepts of the species (biological, ecological, morphological, genetic and phylogenetic concepts) (j) Explain how new species are formed with respect to geographical isolation (allopatric speciation) and behavioural or physiological isolation withi n the same geographical location (sympatric speciation) 3. References Campbell, N.A. and Reece, J.B. (2008). Biology, 9th edition. Pearson. Contents 1. Introduction ............................................................................................................... 1 2. Learning Outcomes.................................................................................................... 1 3. References ................................................................................................................. 1 4. Concepts of Species ................................................................................................... 2 5. Speciation .................................................................................................................. 5

2 EJC H2 Biology T2W1 Evolution 1B 4. Concepts of Species Biological species concept A species is a group of organisms capable of interbreeding and producing fertile, viable offspring . Organisms of the same species are reproductively isolated from those of a different species. (Note: For most purposes, the biological species concept is used.) Advantage: To determine if organisms are of the same species, they can be studied to see if they can interbreed and produce fertile, viable offspring. Limitation: 1) This definition of species cannot be applied to asexually reproducing organisms and extinct species whose breeding behaviour cannot be observed in nature. 2) In plants, two different species can mate and give rise to viable hybrids offspring that are potentially fertile because t hey are capable of polyploidy. Polyploidy is rare in animals. Genetic species concept A species is a group of genetically compatible interbreeding organisms in a natural population that is genetically isolated from other such groups. Organisms in a species have sufficient similarity in their DNA sequences and share the same number of chromosomes. The focus on genetic isolation rather than reproductive isolation distinguishes the Genetic Species Con