I have collected some examples of speciation that are handy to have available when a creationist claims there are none.
We have of course directly observed the emergence of new species, conclusively demonstrating common descent, a core hypothesis of evolutionary theory. This is a much a "proof" of evolution as dropping a bowling ball on your foot "proves" gravity.
Edit 2018, this is a real classic. Darwin's Finches had a recent rapid speciation by hybridization;
Here is another. These are gall flies diverging based on host plant selection which is similar to Apple Maggot Fly (Rhagoletis pomonella discussed below;
Craig, T. P., Itami, J. K., Abrahamson, W. G., & Horner, J. D. (1993). Behavioral evidence for host-race formation in Eurosta solidaginis. Evolution, 1696-1710.
There was a very odd example just pointed out to me that could not have occurred in nature, "Laboratory synthesis of an independently reproducing vertebrate species"
Here we report the generation of four self-sustaining clonal lineages of a tetraploid species resulting from fertilization of triploid oocytes from a parthenogenetic Aspidoscelis exsanguis with haploid sperm from Aspidoscelis inornata.
A multi-species review is;
Abrahamson, W. G., Eubanks, M. D., Blair, C. P., & Whipple, A. V. (2001). Gall flies, inquilines, and goldenrods: a model for host-race formation and sympatric speciation. American Zoologist, 41(4), 928-938.
Here is one I had missed before now (14 Aug, 2014):
"Speciation By Hybridisation In Heliconius Butterflies" Jesús Mavárez, Camilo A. Salazar, Eldredge Bermingham, Christian Salcedo, Chris D. Jiggins and Mauricio Linares, Nature, 441: 868-871 (15th June 2006)
I want to add a link to Cornell University biologist Allen MacNeill's blog article on the emergence of new species.
A new emerging species is added to the list from a recent publication, “Hybrid speciation in sparrows I: phenotypic intermediacy, genetic admixture and barriers to gene flow” (JO S. HERMANSEN, STEIN A. SÆTHER, TORE O. ELGVIN, THOMAS BORGE, ELIN HJELLE, GLENN-PETER SÆTRE, Molecular Ecology, Volume 20, Issue 18, pages 3812–3822, September 2011). What makes this particular example interesting is four fold. First, it is a bird species, and vertebrate examples are less common. Second, it resulted from a hybrid between two similar species, which has not been considered a likely pathway to speciation in vertebrates. Third, the researchers have been able to identify the actual genetic differences between the three species. Finally, the event is incomplete, and still in process.
A large review of multiple species is, Sergey Gavrilets and Jonathan B. Losos "Adaptive Radiation: Contrasting Theory with Data" Science 6 February 2009 323: 732-737
Some specific examples for plants, insects, fish, birds, lizards and mammals follows.
Here are five examples sampled from: "Observed Instances of Speciation" by Joseph Boxhorn, 1995
Evening Primrose (Oenothera gigas)
While studying the genetics of the evening primrose, Oenothera lamarckiana, de Vries (1905) found an unusual variant among his plants. O. lamarckiana has a chromosome number of 2N = 14. The variant had a chromosome number of 2N = 28. He found that he was unable to breed this variant with O. lamarckiana. He named this new species O. gigas.
Vries, H.D., 1905. Ueber die Dauer der Mutations-periode bei Oenothera Lamarckiana. Berichte der Deutschen Botanischen Gesellschaft, 23, p.382.
(Added April 11, 2011)
The former “Answers in Genesis” gang claims they have found a problem with using O. gigas as an example of polyploidal speciation. There are so many good examples of new species emerging, both in the wild, and in laboratories, that I would not want to use one that is incorrect.
The notorious creationist website “Creation Ministries,” disputes O. gigias as a valid example of polyplodial speciation. (Feedback, March 31, 2007 “Speciation Observed? Was this Evolution?” http://creation.com/evolution-by-fiat-and-faith#specob As I have found them to be grossly wrong on many occasions, I also checked their citation list. The creationist claim that O. gigas is not an example of speciation has only two supports; an article in 1943, and that they did not find botanical materials named O. gigias in on-line Botanical nomenclature reference collections. Oenothera names are a mess, but not as bad as Asteracea. O. gigias was apparently found to be a synonym, and is disused. This is trivial, and does nothing to change using the spontaneous emergence of the tetraploidal new species.
The “Creation Ministries International” phonies also cited a 1943 plant genetics article, “An amphidiploid in the F1 generation from the cross Oenothera franciscana x Oenothera biennis, and its progeny” (Davis, B.M., Genetics 28(4):275–285, July 1943). It is available on-line in PDF at: http://www.genetics.org/cgi/reprint/28/4/275.pdf
Read it for yourselves, if you like. It has nothing relevant to de Vries, or his O. gigias being used as valid examples of speciation. This is the sort of misrepresentation typical from professional creationists, who expect their followers to lack either the education, or motivation to actually dig through the science.
For a more recent review of the role polyplodial plants play in evolution, read;
"Duplicate genes increase expression diversity in closely related species and allopolyploids" Misook Haa, Eun-Deok Kima and Z. Jeffrey Chen, PNAS February 17, 2009 vol. 106 no. 7 2295-2300
And, here is a broader review on plant evolution and genome doubling that is also a bit easier to read;
"Genetic and epigenetic alterations after hybridization and genome doubling" Ovidiu Paun, Michael F. Fay, Douglas E. Soltis, and Mark W. Chase, Taxon. 2007 August; 56(3): 649–56.
Kew Primrose (Primula kewensis)
Digby (1912) crossed the primrose species Primula verticillata and P. floribunda to produce a sterile hybrid. Polyploidization occurred in a few of these plants to produce fertile offspring. The new species was named P. kewensis. Newton and Pellew (1929) note that spontaneous hybrids of P. verticillata and P. floribunda set tetraploid seed on at least three occasions. These happened in 1905, 1923 and 1926.
Owenby (1950) demonstrated that two species in this genus were produced by polyploidization from hybrids. He showed that Tragopogon miscellus found in a colony in Moscow, Idaho was produced by hybridization of T. dubius and T. pratensis. He also showed that T. mirus found in a colony near Pullman, Washington was produced by hybridization of T. dubius and T. porrifolius. Evidence from chloroplast DNA suggests that T. mirus has originated independently by hybridization in eastern Washington and western Idaho at least three times (Soltis and Soltis 1989). The same study also shows multiple origins for T. micellus.
Dobzhansky and Pavlovsky (1971) reported a speciation event that occurred in a laboratory culture of Drosophila paulistorum sometime between 1958 and 1963. The culture was descended from a single inseminated female that was captured in the Llanos of Colombia. In 1958 this strain produced fertile hybrids when crossed with conspecifics of different strains from Orinocan. From 1963 onward crosses with Orinocan strains produced only sterile males. Initially no assortative mating or behavioral isolation was seen between the Llanos strain and the Orinocan strains. Later on Dobzhansky produced assortative mating (Dobzhansky 1972).
Apple Maggot Fly (Rhagoletis pomonella)
Rhagoletis pomonella is a fly that is native to North America. Its normal host is the hawthorn tree. Sometime during the nineteenth century it began to infest apple trees. Since then it has begun to infest cherries, roses, pears and possibly other members of the rosaceae. Quite a bit of work has been done on the differences between flies infesting hawthorn and flies infesting apple. There appear to be differences in host preferences among populations. Offspring of females collected from on of these two hosts are more likely to select that host for oviposition (Prokopy et al. 1988). Genetic differences between flies on these two hosts have been found at 6 out of 13 allozyme loci (Feder et al. 1988, see also McPheron et al. 1988). Laboratory studies have shown an asynchrony in emergence time of adults between these two host races (Smith 1988). Flies from apple trees take about 40 days to mature, whereas flies from hawthorn trees take 54-60 days to mature. This makes sense when we consider that hawthorn fruit tends to mature later in the season that apples. Hybridization studies show that host preferences are inherited, but give no evidence of barriers to mating. This is a very exciting case(Rhagoletis pomonella). It may represent the early stages of a sympatric speciation event (considering the dispersal of R. pomonella to other plants it may even represent the beginning of an adaptive radiation).
What I find personally fascinating is that the increasing genetic isolation of the two races of R. pomonella has led to the reproductive isolation/speciation of the parasitic wasp Diachasma alloeum (Hymenoptera: Braconidae) which feeds on the rapidly evolving fly. (See "Sequential Sympatric Speciation Across Trophic Levels" Andrew A. Forbes, Thomas H.Q. Powell, Lukasz L. Stelinski, James J. Smith, Jeffrey L. Feder, Science 6 February 2009 323: 776-779).
So, even when there might still be limited inter-fertility in the diverging, R. pomonella, there is already a related speciation in an associated insect.
Here are two speciation examples sampled from: "Some More Observed Speciation Events, 1992-1997" by Chris Stassen, James Meritt, Anneliese Lilje, L. Drew Davis
Rapid speciation of the Faeroe Island house mouse, which occurred in less than 250 years after man brought the creature to the island. (Test for speciation in this case is based on morphology. It is unlikely that forced breeding experiments have been performed with the parent stock.) Reference: Stanley, S., 1979. Macroevolution: Pattern and Process, San Francisco, W.H. Freeman and Company. p. 41
Formation of five new species of cichlid fishes which formed since they were isolated less than 4000 years ago from the parent stock, Lake Nagubago. (Test for speciation in this case is by morphology and lack of natural interbreeding. These fish have complex mating rituals and different coloration. While it might be possible that different species are inter-fertile, they cannot be convinced to mate.) Reference: Mayr, E., 1970. Populations, Species, and Evolution, Massachusetts, Harvard University Press. p. 348
Nevo, E., 1991, Evolutionary Theory and process of active speciation and adaptive radiation in subterranean mole rats, spalax-ehrenbergi superspecies, in Israel, Evolutionary Biology, Volume 25, pages 1-125.
There is a large literature on new species emerging among newly introduced colonies of Anole lizards. Here are just a few examples:
Anolis oculatus undergoes rapid subpopulation isolations following drought, or the introduction of a preditor, Anolis sagrei. Reference: Roger S. Thorpe "Population Evolution and Island Biogeography" Science 16 December 2005 310: 1778-1779
New species of Anolis on Indian Ocean Islands. Reference: Marguerite A. Butler, Stanley A. Sawyer, Jonathan B. Losos "Sexual dimorphism and adaptive radiation in Anolis lizards" Nature 447, 202 - 205 (10 May 2007)
Anurag A. Agrawal "Phenotypic Plasticity in the Interactions and Evolution of Species" Science 12 October 2001 294: 321-326
This next one is very interesting. It is a vertebrate (a lizard species), and the new species was produced experimentally as a hybrid cross. This is the same kind of genetic novelty as found in plants, e.g. Evening Primrose (Oenothera gigas) that I mentioned earlier.
"Laboratory synthesis of an independently reproducing vertebrate species" Aracely A. Lutesa, Diana P. Baumann, William B. Neaves, and Peter Baumann (Published online before print PNAS May 4, 2011, doi: 10.1073/pnas.1102811108)
Speciation in animals commonly involves an extrinsic barrier to genetic exchange followed by the accumulation of sufficient genetic variation to impede subsequent productive interbreeding. All-female species of whiptail lizards, which originated by interspecific hybridization between sexual progenitors, are an exception to this rule. Here, the arising species instantaneously acquires a novel genotype combining distinctive alleles from two different species, and reproduction by parthenogenesis constitutes an effective intrinsic barrier to genetic exchange. Fertilization of diploid parthenogenetic females by males of sexual species has produced several triploid species, but these instantaneous speciation events have neither been observed in nature nor have they been reconstituted in the laboratory. Here we report the generation of four self-sustaining clonal lineages of a tetraploid species resulting from fertilization of triploid oocytes from a parthenogenetic Aspidoscelis exsanguis with haploid sperm from Aspidoscelis inornata. Molecular and cytological analysis confirmed the genetic identity of the hybrids and revealed that the females retain the capability of parthenogenetic reproduction characteristic of their triploid mothers. The tetraploid females have established self-perpetuating clonal lineages which are now in the third generation. Our results confirm the hypothesis that secondary hybridization events can lead to asexual lineages of increased ploidy when favorable combinations of parental genomes are assembled. We anticipate that these animals will be a critical tool in understanding the mechanisms underlying the origin and subsequent evolution of asexual amniotes.
The is also discussed on the Web at Panda's Thumb, and Nobel Intent.
One more on fish;
Andrew P. Hendry, John K. Wenburg, Paul Bentzen, Eric C. Volk, Thomas P. Quinn "Rapid Evolution of Reproductive Isolation in the Wild: Evidence from Introduced Salmon" Science 20 October 2000: Vol. 290. no. 5491, pp. 516 - 518
So, common descent is established by direct observation of speciation, and various selective pressures are seen to be effective. Depending on population size, and starting variability, selective pressures can be strongly acting resulting in rapid emergence of new species.