Hybridization and Polyploidy

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Excerpt In previous installations of this column, we have discussed the fact that brand-new species of plants and animals suddenly appear in the fossil record bearing remarkable similarities to related species. Automatically credited to Darwinian evolution... Continue reading

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This article was first published in the May 2006 ABR Electronic Newsletter.


In previous installations of this column, we have discussed the fact that brand-new species of plants and animals suddenly appear in the fossil record bearing remarkable similarities to related species. Automatically credited to Darwinian evolution, in many cases these new species, similar to but noticeably different from their near relatives, are actually the result of hybridization between two different species within the greater created kind (the Hebrew miyn of Genesis 1:11, translated genus in the Latin Bible). Several examples of this, occurring before scientists' very eyes, have been mentioned in this column.

Robbin C. Moran, Curator of Ferns at the New York Botanical Garden, has observed this phenomenon with common ferns and lycophytes, a genus of plants that, like ferns, reproduce via spores. In an article in the journal Natural History, Moran pointed out that scientists who study ferns now make use of reticulograms, scientific diagrams that "depict the relationships between species and their hybrids, showing which species have come together to form which hybrids" (Moran 2004: 55). Reticulograms also show which hybrids are sterile (producing non-viable offspring), or fertile (producing viable offspring). According to Moran, almost all hybrids start off as sterile, but if they double their number of chromosomes through a process called polyploidy, "they automatically become fertile" (ibid.).

According to Moran, a large number of species have popped into existence through hybridization and polyploidy rather than through Darwinian evolution. Referring to the second volume (Pteridophytes and Gymnosperms) of the Flora of North America, published in 1993, which was the first scientific treatise on plants to include reticulograms, Moran wrote: "Of the 420 species of ferns and lycophytes described in the treatise, about a hundred originated as hybrids and later became fertile through polyploidy" (ibid.).

Plant polyploidy happens in nature when an abnormality occurs in the cell division that produces spores. Usually, a spore gets only one chromosome from each pair of chromosomes in the parent plant, but sometimes that doesn't happen, and instead a spore gets a full contingent of chromosomes (meaning two of each pair). Once this abnormal spore germinates, the resultant eggs and sperm also carry the double contingent of chromosomes. "That," says Moran, "sets the stage for polyploidy" (ibid. 56).

Hybrids, on the other hand, come about when the sperm from one species of fern fertilizes the egg of another species. The resultant hybrid grows into a normal plant, but it is sterile. This is because during the cell division that produces reproductive spores, the chromosomes of the two parent plants don't pair up properly (if at all), and are then distributed unequally to the daughter cells (ibid.). Often, however, polyploidy steps in to work with hybridization to create new species within the greater fern miyn. Moran explains:

If polyploidy leaves two copies of each chromosome in a hybrid's cells, each chromosome gets a partner that is an exact duplicate of itself. During spore formation in the hybrid, normal pairing of chromosomes can take place, and the chromosomes can be distributed equally to the spores. The new plant is now fertile, able to disperse and reproduce, SOMETIMES BEYOND THE RANGES OF ITS PARENTS (Ibid. [emphasis added]).

This fits in well with a Genesis framework: after the original creation of plants "according to their miyn/genus/kind," the fern miyn/genus began to spread across the globe, undergoing a combination of hybridization and polyploidy as the years progressed, with each new fern species spreading slightly farther than the geographical range of its parent species. Appearing in the fossil record, this would certainly create the impression that these new species sprang up as the result of evolution, when it could just as well have been what is still occurring today for scientists to witness and report on: the creation of new species through hybridization that produces viable offspring via polyploidy.

Recommended Resources for Further Study

     
The Myth of
Natural Origins
The Big Argument The Genesis Record

Reference
Moran, Robbin C. 2004. "Dispatches from the Fern Frontier." Natural History 113, no. 8.

Stephen Caesar holds his master's degree in anthropology/archaeology from Harvard. He is a staff member at Associates for Biblical Research.

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