Main problems with evolution: speciation

Photo: Hemp-nettle, by Ivar Leidus, CC BY-SA 3.0 via Wikimedia Commons.

Editor’s Note: We are delighted to present a series by biologist Jonathan Wells on the main scientific problems related to evolution. This is the seventh entry in the series, taken from the new book The Complete Guide to Science and Faith: Exploring the Ultimate Questions About Life and the Cosmos. Find the complete series to date here.

We know that speciation has happened because many new species have appeared in the history of life. Evolutionary biologist Ernst Mayr wrote: “Darwin called his excellent work About the origin of speciesfor he was fully aware that the transition from one species to another was the most fundamental problem of evolution.1 According to evolutionary biologist Douglas Futuyma, speciation “is the sine qua non of diversity” necessary for evolution. Speciation “stands on the border between microevolution – genetic changes within and between populations – and macroevolution”.2

But how does speciation occur?

Part of the problem is that the term species is notoriously difficult to define. A definition applicable to plants and animals will not necessarily work for bacteria, and definitions applicable to living things will not necessarily work for fossils. In 2004, several dozen definitions were used by biologists and paleontologists.3 The definition most often used by evolutionary biologists is the “concept of biological species”, according to which species are groups of natural populations that reproduce and are isolated from other such groups.4

If species are defined this way, then, in a sense, speciation has been observed in the laboratory. Normally, when two different species hybridize, either naturally or artificially, the hybrids are sterile because the maternal and paternal chromosomes are too dissimilar and cannot pair up during cell division. Sometimes, however, the hybrid undergoes chromosome doubling, or polyploidy. With matching sets of chromosomes that can undergo cell division, the hybrid can then be fertile and constitute a new species according to the concept of biological species. During the first decades of the 20th century, Swedish scientist Arne Müntzing used two species of plants to create a hybrid that underwent chromosome doubling to produce hemp-nettle, a member of the mint family that had previously been found in nature.5

Speciation by polyploidy is called secondary speciation to distinguish it from primary speciation — the splitting of a species into two. According to Douglas Futuyma, polyploidy “does not confer major new morphological characteristics…[and] does not cause the evolution of new genera” or higher levels in the biological hierarchy.6 So, although secondary speciation by polyploidy has been observed in flowering plants, it is not the solution to Darwin’s problem. The solution would be primary speciation by variation and selection, which has not been observed.

Darwin and the nascent species

In 1940, geneticist Richard Goldschmidt argued that “the facts of microevolution are not enough to understand macroevolution”. He concluded: “Microevolution does not lead beyond the limits of the species, and the typical products of microevolution, the geographic races, are not nascent species.”seven

Darwin used the term nascent species to designate a variety of a species which he thought was becoming a new species: “I believe that a well-marked variety may justly be called an incipient species.8 But how do you know if two varieties (or races) are becoming distinct species? Saint Bernards and Chihuahuas are two varieties of the canine species (Canis lupis familiaris) which, for anatomical reasons, do not intersect naturally. Are they on the way to becoming full-fledged species? The Ainu people of northern Japan and the !Kung of southern Africa are members of the human species (Homo sapiens sapiens). While people from both groups can undoubtedly interbreed, without modern technology, which allows massive movement of people around the world, they would be (for all intents and purposes) reproductively isolated geographically, linguistically and culturally. Are they then nascent species? Clearly, Darwin’s term nascent species is a theoretical prediction, not a proof.

Origin of a new species?

We sometimes read in the media that scientists have finally observed the origin of a new species. Such cases, however, are invariably either examples of incipient speciation or cases in which scientists have inferred from already existing species how they might have divided in the past.9 Observational evidence for primary speciation is still lacking.

In 1992, evolutionary biologist Keith Stewart Thomson wrote, “An unfinished business for biologists is the identification of the smoking gun of evolution”, and “the smoking gun of evolution is speciation, not local adaptation. and population differentiation. Before Darwin, Thomson explained, the consensus was that species could only vary within certain limits; indeed, centuries of artificial selection had apparently experimentally demonstrated such limits. “Darwin had to show that limits could be exceeded,” Thomson wrote, and “so can we.”ten

In 1996, biologists Scott Gilbert, John Opitz and Rudolf Raff wrote:

Genetics might be enough to explain microevolution, but microevolutionary changes in gene frequency were not thought to be able to turn a reptile into a mammal or a fish into an amphibian. Microevolution looks at adaptations that concern the survival of the fittest, not the arrival of the fittest.

They concluded: “The origin of species – Darwin’s problem – remains unsolved.”11

Primary speciation evidence

English bacteriologist Alan Linton searched for evidence of primary speciation and concluded in 2001:

None exist in the literature claiming that one species has been shown to evolve into another. Bacteria, the simplest form of independent life, are ideal for this kind of study, with generation times of twenty to thirty minutes, and populations reached after eighteen hours. But throughout the 150 years of the science of bacteriology, there is no evidence that one species of bacteria has changed into another…Since there is no evidence of species changes between simplest forms of single-celled life, it is not surprising that there is no evidence for prokaryotic evolution [e.g., bacterial] eukaryotic [e.g., plant and animal] cells, not to mention the whole range of higher multicellular organisms.12

In 2002, evolutionary biologists Lynn Margulis and Dorion Sagan wrote: “Speciation, whether in remote Galapagos, in the laboratory cages of fruit flies [those who study fruit flies]or in the cluttered sediments of paleontologists, has never yet been directly traced.13 So evolution’s smoking gun is still missing.

Followingthe last entry in the series, “Darwin’s One Wrong Argument”.

Remarks

  1. Ernest Mayr, The growth of biological thought (Cambridge, MA: Harvard University Press, 1982), 403.
  2. Douglas J. Futuyma, Evolution (Sunderland, MA: Sinauer Associates, 2005), 401.
  3. Jerry A. Coyne and H. Allen Orr, Speciation (Sunderland, MA: Sinauer Associates, 2004), 25.
  4. Mayr, The growth of biological thought, 273; Coyne and Orr, Speciation26-35.
  5. Arne Müntzing, “Cytogenetic investigations of Tetrait Galeopsis“, Heritage 16 (1932), 105-154.
  6. Futuima, Evolution398.
  7. Richard Goldschmidt, The material basis of evolution (New Haven, Connecticut: Yale University Press, 1940), 8, 396.
  8. Charles Darwin, The origin of species, 1st ed., 52, http://darwin-online.org.uk/content/frameset?pageseq=67&itemID=F373&viewtype=side (accessed August 23, 2020).
  9. Jonathan Wells, The Politically Incorrect Guide to Darwinism and Intelligent Design (Washington, DC: Regnery, 2006), 52-55.
  10. Keith Stewart Thomson, “Natural Selection and the Smoking Gun of Evolution”, American scientist 85 (1997), 516-518.
  11. Scott F. Gilbert, John M. Opitz, and Rudolf A. Raff, “Resynthesizing Evolutionary and Developmental Biology,” Developmental biology 173 (1996), 357-372.
  12. Alan H. Linton, “Scarce Research on Creator,” Times Higher Education Supplement (April 20, 2001), Book Section, 29.
  13. Lynn Margulis and Dorion Sagan, Acquiring genomes: a theory of the origins of species (New York: Basic Books, 2002), 32.