No one has ever seen one species arise from another.
I. Is observation of speciation required?
Most of the evidence for speciation is indirect, as must be the case since (a) speciation typically does not occur on human timescales, and (b) where it does, we must be watching carefully over an extended period of time to notice. This does not make the evidence for speciation weak: on the contrary, it is by far the best explanation for all of the data we have, including the anatomical, molecular, and biogeographical correspondences among organisms. To insist that only direct observation of a speciation event qualifies as evidence for speciation is to misunderstand the nature of scientific evidence and of evidence more generally, akin to arguing that theories about the past cannot be scientific, because the past cannot be observed.
The above notwithstanding, there are examples of observed speciation. Two articles from the talk.origins archive (Boxhorn 2004, Stassen et al.) give numerous examples. Some examples in the articles are inferred rather than observed, and some (see part IV below) are incorrect, but most are what they claim to be. Readers who look at critiques of those two articles should be cautious: the stated intent of the articles is to offer examples of observed speciation, but creationists tend to criticize the articles for not doing something other than that stated intent. Such creationists, given the observed instances of speciation that they asked for, react by imposing arbitrary new constraints (no hybridization, for instance), or retreat to demanding direct observation of something that evolutionists think rarely, if ever, occurs on a human timescale or in a single speciation event (such as massive changes in morphology).
III. Giving credit where it is due
The young-earth creationist organization Creation Ministries International has completely disavowed this argument (CMI n.d.).
IV. Erratum regarding Weinberg et al. (1992)
For a long time, I offered Weinberg et al. (1992) as my primary case example of observed speciation. The paper reports what was thought to be the rapid speciation of Nereis acuminata within the laboratory. However, a reader eventually pointed out to me that the conclusions of the paper were overturned by a later paper co-authored by Weinberg (Rodríguez-Trelles et al. 1996). My thanks go out to the reader for helping to ensure the accuracy of this guide, and my apologies go out to everyone else. I hope everyone understands that this is the way to do it: when someone shows that you have made a mistake, you need to acknowledge it—most of all to yourself—rather than double down.
Boxhorn J. 2004. Observed instances of speciation. http://www.talkorigins.org/faqs/faq-speciation.html. Spotted 21 Nov 2014.
CMI. n.d. Arguments we think creationists should NOT use. creation.com/arguments-we-think-creationists-should-not-use. Spotted 21 Nov 2014.
Stassen C, Meritt J, Lilje A, and Davis LD. 1997. Some more observed speciation events. http://www.talkorigins.org/faqs/speciation.html. Spotted 21 Nov 2014.
Rodríguez-Trelles F, Weinberg JR, and Ayala FJ. 1996. Presumptive rapid speciation after a founder event in a laboratory population of Nereis: allozyme electrophoretic evidence does not support the hypothesis. Evolution 50(1):457-461.
Weinberg JR, Starczak VR, and Jorg D. 1992. Evidence for rapid speciation following a founder event in the laboratory. Evolution 46(4):1214-1220.
Last updated: 21 Nov 2014
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