Species and speciation IntroductionSpeciesis a taxonomic concept used in Biology to refer to a population of organismsthat are in some important ways similar. The idea of species has a longhistory. After thousands of years of use, the concept remains central tobiology and a host of related fields, and yet also remains at times ill-definedand controversial. In this article, the formation and evolution of new specieswill be discussed. Species concepts Thereare mainly five concepts of species.
Biological concept of speciesBiologicalconcept of species is the most commonly used concept. It defines a species as agroup of populations whose members have the potential to interbreed in natureand produce viable, fertile offspring but do not produce viable, fertileoffspring with members of other such groups. (Jane B. Reece, 2015) Members of abiological species are defined in terms of reproductive compatibility. Geneflow is the transfer of alleles between populations. Gene flow occurs betweenthe different populations of a species and the ongoing exchange of alleles tendsto hold the populations together genetically. Individuals who mate and producefertile offspring are considered belong to same species. For example, althoughhorse and donkey can mate and produce mules, mules are non-fertile offspring,so horse and donkeys are still different species.
Ecological concept of speciesTheEcological Species Concept defines a species in terms of its ecological niche,i.e. the sum of how members of the species interact with the non-living andliving parts of their environment. (Jane B. Reece, 2015) For example, twospecies of Galapagos finches may be similar in appearance but distinguishablebased on what they feed on, so they are consider being different species. Thisis less commonly used because niches are generally difficult to identify as it involvesthe interaction between the organism and its environment.
Morphological concept of speciesTheMorphological Species Concept defines a species in terms of its body shape andother structural features. (Jane B. Reece, 2015) This was wildly usedin past day because at that time, molecular biology was no so developed andpeople can only distinguish different species by observing their appearances.
However, this is less useful than the biological concept of species becausesometimes the same living environment give different species similarappearances, so they may be mistakenly regarded as same species while there isno gene flow among them. Morphological concept of species is still wildly usedin daily life but it is less convinced than biological concept. Phylogenetic concept of speciesThePhylogenetic Species Concept defines a species as the smallest group ofindividuals who share a common ancestor, forming one branch on the tree oflife.
(Jane B. Reece, 2015) Genetic concept of speciesTheGenetic Concept of Species defines a genetic species as a group of geneticallycompatible interbreeding natural populations that is genetically isolated fromother such groups. (Jane B. Reece, 2015) Genetic conceptfocuses more on genetic isolation rather than what being discusses underbiological concept, reproductive isolation. Formation andevolution of new species Uniformitariansm and Darwin’s idea Uniformitariansmwas popularized by geologist Charles Lyell’s Priciples of Geology in 1830. He claimed that the earth’s historywas a slow, gradual process punctuated by occasional natural catastrophic events.(Wikipedia, 2018) Uniformitariansm hasthe assumption that natural laws are the same in different fields. Darwin washeavily influenced by Lyell’s idea and became a supporter of uniformitariansm.
Inthe aspect of evolution, he believed that the evolution process was also a slowbut continuous process. In1859, Darwin published On the Origin ofSpecies and stated his hypothesis of evolution in the book. This ushered ina scientific revolution—the era of evolutionary biology. He mainly addressedtwo ideas in the book, descent with modification and natural selection. Descentwith modification means that many species on earth today are descendants ofancestral species (Jane B. Reece, May 20, 2015) .
During the process,genetic changes occurred and led to the differences among species. Over time,populations were evolved to different species but they are related because theyhave a common ancestor. On the other hand, natural selection is the mechanismof those evolutionary changes. In other words, new species are formed base on ancestralorganisms, the force that driven them to evolve is natural selection. Thereare many evidence supporting Darwin’s idea, one of them is the fossil record.Although current found fossils do show the trend of continuous evolution ofspecies, there are still missing links in between. Darwin believed the missingstages were present but just not found by us.
However, some scientists proposedopposite opinions. Catastrophism to punctuated equilibriumCatastrophismwas popularized by George Cuvier, a French naturalist. He was strongly againstto Darwin’s evolution theory. He believed that the species that appeared asfossil will not evolve any more, until the species became extinct, its anatomywill remain unchanged. That was the former idea of punctuated equilibrium.
In1972, Niles Eldredge and Stephen Jay Gould proposed the ide of punctuated equilibrium.It stated that the evolution and formation of species was a sudden event butnot continuously evolved from the ancestral species. At certain occasion,evolution suddenly occurs at a rapid rate, new species burst out. After that,the species will enter a relatively constant phase where no evolution processtakes place, this is called the equilibrium.
The punctuated equilibrium theoryprovided an alternative explanation on the missing links in fossil records.Punctuated equilibrium is not a theory that against Darwin’s evolution theorybut an add-on to it. Modern evolutionary ideas and synthesisModernsynthesis compiles Darwin’s theory with Mendel’s genetics, redefined the theoryof evolution. The concepts in the modern synthesis theory are natural selection,genetic variations and isolation mechanisms that lead to speciation. (BYJU’s biology, February 23, 2017)Thenatural selection factory in modern synthesis theory is similar to Darwin’stheory, both of them agree that natural selection is the force that drivenevolution. Modern synthesis added on genetic variations concept to evolution.Base on Mendel’s theory and its extension, the recombination of new genotypesmany form new species. During meiosis, the crossing over process also allowsgene recombination.
Furthermore, mutations also caused variations in offspringthat may lead to the formation of new species. Thereare three main isolating mechanisms which give rise to speciation, namely, geographicalisolation, physiological isolation and behavioural isolation. Geographicalisolation gives rise to allopatric speciation. In allopatric speciation, geneflow is interrupted when a population is divided into geographically isolatedsubpopulations. Once geographic separation has occurred, the separated genepools may diverge. Different mutations arise, and natural selection and geneticdrift may alter allele frequencies in different ways in the separatedpopulations.
Reproductive isolation may then arise as a by-product of selectionor drift having caused the populations to diverge genetically. Physiologicaland behavioural isolation gives rise to sympatric speciation. In sympatric speciation,speciation occurs from a population that lives in the same geographic area andgene flow is interrupted by reproductive barriers.
In physiological isolation, matingis attempted but morphological differences prevent its successful completion.In behavioural isolation, courtship rituals that attract mates and otherbehaviours unique to a species are effective reproductive barriers, evenbetween closely related species. Such behavioural rituals enable materecognition – a way to identify potential mates of the same species.