Hybridization (Research Article)

Hybridization (Research Article)

We’ve referenced hybridization multiple times throughout this article series but not discussed what it is. To an extent that is not needed.  Most people somewhat intuitively know what a hybrid is. However, given what we discussed about species in earlier chapters, an in-depth analysis is needed to determine what we mean when we discuss hybridization.

Hybridization is the processes of two species or varieties breeding together to create an offspring or potentially a new variety or species.  Creating a hybrid is thus a reproductive process. No one disputes that. The term hybrid is somewhat unspecific, however.  Crossbreeding a Great Dane and German Sheppard dog will produce a hybrid, even though they are the same species, just like crossing a wolf and a coyote which are different species. This leads to inevitable confusion over whether two species are involved or not. In order to avoid confusion, I will refer to the result of breeding of two varieties as a mixta from the Latin “mixed” and retain hybrid for between species breeding for the moment. I will expound on this in a moment.

Interbreeding

What does hybridization imply? This question is surprisingly complex to answer.  The obvious answer is interbreeding between species.  Mayr pointed out the importance of interbreeding as part of a definition of species. “With increasing frequency since then, interbreeding has been considered a decisive criterion in species definitions.[1]” Yet this would seem to imply complete reproductive isolation in species in the natural world, something Coyne and Orr point out is not correct. “In our view, distinct species are characterized by substantial but not necessarily complete reproductive isolation[2].” They are probably closer to the truth in this regard, as species regularly interbreed and produce new species[3][4][5].  Coyne and Orr tacitly admit this. “Fusion of species through hybridization contradicts Mayr’s view that speciation is not complete until it is irreversible.[6]

Some of the more astute readers may have noticed that discussing hybridization in this manner is making a major assumption. Hybridization between species assumes that species actually exist as units of nature. As we demonstrated in previous articles, this is simply not true. Simpson called the species arbitrary[7].  Coyne and Orr admit that the reality of species cannot be proved[8]. One author recognized this problem, particularly when applied to asexual organisms. “Thus, it will be impossible to objectively draw the line between lineages that can be assigned to the species rank, those that merely represent variation within a species, and those that represent groups of species.[9]” Given that the vast majority of organisms on earth are asexual, this only extends the species problem. The author has essentially admitted that there is no true species for the vast majority of creatures on earth.  Yet if that as true, as mentioned before, there is no real species concept.  This places evolution in a difficult position because ““…Speciation continues to be so crucial a point as frequently to be considered virtually synonymous with evolution.[10]” If there are no real species, then there is no speciation, which means no evolution, by their own words.

Scientists have recognized the problem species represent to their dogma since at least the 1950s! One author went so far as to call the species concept completely false. “Such highly abstract fictions as “species”, in the conventional abstract sense, will only continue to obscure such discussions.[11]” Yet evolutionists continue to tout species as “real biological entities”[12]. This in spite of the fact that the species concept has been known not to exist for nearly seventy years! The reason for this is likely ideological rather than scientific. If speciation is removed, evolution has no mechanism. “In sexually reproducing organisms diversification in evolution is due to speciation.[13]” Remove speciation, and evolution no longer works.

Some evolutionists have attempted to salvage the species concept that they so desperately need by resorting to a callous pragmatism. They pull from the taxonomic species concept discussed in chapter two.  This concept originated with Darwin and glibly says that “…a species is a species if a competent systematist says it is.[14]“ While this is a very practical application, it does nothing for the reality of the species concept. In fact, resorting to this concept admits that the species is arbitrary in that it is defined by whatever scientist is looking at it.

This affects hybridization in a very unique way. If there are no true species, then what we have is not true hybridization, but mixta. Let me explain what I mean. Mixta is the breeding between two of the same type of organism, different varieties of the same species according to scientists.  Hybridization is the breeding between two species. However, if species are not a real concept, which it is not, then true hybridization does not exist.  All that exists is mixta, breeding within varieties of a higher grouping, in this case, the Biblical kind.

Note that I did not say that breeding between species does not happen. It clearly does.  However, hybridization as a concept is breeding between two distinct groups. As we have established, the species concept does not exist in nature.  It is arbitrary. So, breeding between species does happen, but it is not hybridization because species are not true distinct groupings.  True hybridization would be between two different groupings that are units of nature. As we established in preceding chapters, only the Biblical baramin are true units of nature, and thus are the only groupings that are not arbitrary. Thus, true hybridization would be breeding between the Biblical kinds, which has never been observed.

The mixta concept, on the other hand, is breeding within a grouping and thus works perfectly for our purposes.  The natural grouping, the created kind, allows for mixta to occur freely within them. Of course, in the post-fall, post-flood world, genetic variation may have occurred to reproductively isolated organisms. As part of the fallen world, every genome, including ours, undergoes breakdown, called entropy.  This breakdown may have helped contribute to post-flood speciation and reproductive isolation.

Defining Hybrids

This section could have been titled “Defining Mixta” and probably would have been more appropriate. However, since the ruling scientific paradigm is unlikely to adopt my proposed term anytime soon, I will use hybrid and mixta synonymously from this point forward unless I am speaking of proposed breeding between the kinds, where I will use “true hybrid” to emphasize what I mean.

The mixta represents any interbreeding between members of the same created kind. In order to understand this, we need to take it in context of what we observe in the natural world. For this example, we will take the bear baramin, or the Ursidae kind.  The bears were delineated their own kind as part of the Answers in Genesis Ark Encounter project. There is a wealth of hybrid data connecting the various species of bears with the exception of the panda[15].  In fact, there is strong genetic evidence that brown and polar bears regularly interbreed, despite being distinct species, and that their hybrids tend to live in brown bear territory, though polar bears do share some brown bear mitochondrial DNA.  In fact, one study demonstrated that nearly nine percent of the brown bear genome is from polar bears[16]. There is also evidence that polar bears and grizzly bears at least periodically interbreed in the wild[17].

From this interbreeding evidence, we can make some determinations. The above-cited bears share home ranges in at least some places. Where they overlap, they interbreed, in some cases regularly and freely. Take the brown bears for example. They have a widespread range across Eurasia, North America and even parts of China and the Middle East. Obviously, the Chinese bears are not interbreeding with polar bears. Their ranges do not overlap.  Nor are polar bears in Greenland interbreeding with brown bears. Again, ranges do not overlap. But where they do overlap, they mate. This is troublesome for the evolutionary species, but not to the baramin. These hybrids simply illustrate the mixta process that goes on within the created kinds.  It is likely that, were bear populations all found in a similar range, where they overlapped a population of bears would arise resembling the original created kind as the isolated populations freely hybridized and exchanged genetic information.

In an ultimate sense, hybridization between species, the mixta process, is a mixing of the genomes.  Recall from earlier we discussed members of genus Xiphophorus and their ability to freely hybridize and produce fertile offspring. There are twenty-eight species in the genus and at least some of them freely hybridize. They are kept in the pet trade and sold under the name’s swordtails and platys.  Having personally kept these, I can attest how easy it is to both keep and breed them. I can also attest how willingly they interbreed. In fact, hybrids of this genus are regularly used as research organisms, particularly for cancer research[18].  However, only a few species of Xiphophorus are widespread in nature and overlap one another. When they do overlap though, they interbreed freely[19].  This interbreeding process can produce new genetic species, as mentioned in a prior chapter, but just as often it produces mixta[20]. Mixta certainly could develop into a new species, if reproductively isolated and given at least a small population to work with. Marsh recognized this. “It is of great importance to observe the fact illustrated here that the most that hybridization can do in the matter of change is to give rise to another variant, in these instances called a “new species”, within some already existing kind.[21]”  This is particularly true since “In general, speciation is not directly observed but merely adduced after the fact.[22]” In fact, this quote illustrates that most of the time speciation is not observed. Evolutionists like to postulate that this is due to long ages, However, often the speciation process happens so fast that no scientist has a chance to observe it happen, such as in polyploid speciation which is, as mentioned previously, instantaneous.

Very few people question that species form. However, all speciation is in a genetic sense, is a loss of available variation when populations split.  On occasion, two of these populations come together, as they did in some species of Xiphophorus and breed together. This effectively increases the available genetic material to both species as they hybridize. Note that while the hybrid population gains genetic information, no truly new information is introduced.  If the geography changes and the species no longer overlap then the mixed population in the middle can either be absorbed into one species or, alternatively can form its own species.  Thus, the hybrid or mixta in the sense science considers it, is any breeding between two species distinct species. It has the potential to produce a new species as well if it becomes reproductively isolated.

However, because the species is arbitrary, practically defining a hybrid is next to impossible. One scientist’s hybrid might be another scientist’s purebred.  The squabble over guppies illustrates this well.  Endler’s livebearer (Poecilia wingei) is considered its own species and freely hybridized with guppies (Poecilia reticulata)[23]. However, in 2009, a third species was elevated from within P. reticulata called Poecilia obscura. The researchers noted that “P. obscura was most probably not recognized so far as a separate species, because these fish are not different from P. reticulata in the most obvious character of guppies, namely male coloration and pigmentation pattern most of them being linked to sex chromosomes.[24]” In other words, some scientists thought it was part of the P. reticulata species, while others did not and gave it a species of its own.  So, if P. obscura were to freely breed with P. reticulata is that a hybrid or simply breeding within the species? This is why the mixta concept works better for defining this kind of breeding. It is based in a non-arbitrary concept, the Biblical kind, rather than an arbitrary one.

Successful Hybridization

 This may seem like a meaningless question. After all, offspring is the test of hybridization, right? Unfortunately, it is not that simple.  What if the gametes fuse but the embryo dies in vitro? Is that successful hybridization? This question has puzzled baraminologists since Marsh. “True fertilization is necessary because in hybridization the union of gametes may result in an embryo which does not live beyond the gastrula stage; or the fetus may die at full period; or the hybrid may be a healthy individual in every way except it is sterile; or the hybrid may be a completely normal, fertile individual. The requirement for true fertilization is met when the chromosome groups of both parents take part in the formation of the early blastomeres of the embryo.[25]”  Marsh’s idea was that, so long as gametes fused and both parent’s DNA took part in the first few cell divisions, then the two creatures could successfully hybridize. However, in this, he was mistaken.

As noted in a previous article, researchers with less than correct ethics have combined hamster gametes with human gametes in the lab and produced several cell divisions[26]. This was also done with mice[27]. Since the Bible clearly delineates man as being made in the image of God, apart from the animals which were not, they are separate kinds and should not Biblically be able to interbreed[28]. Thus, based on the Bible, we must exclude simple fertilization as the delineator of a successful mixta.

Recognizing this, Siegfried Scherer proposed a slightly better definition. “Two individuals belong to the same basic type if embryogenesis of a hybrid continues beyond the maternal phase, including subsequent coordinated expression of both maternal and paternal morphogenetic genes.[29]” Essentially what Scherer means is that two species are the same kind if the fertilized egg continues development beyond a few cell divisions. While this definition is certainly better than the one proposed by Marsh, observational data to support it is lacking.

This is hardly surprising. The ruling paradigm devotes millions, perhaps billions of dollars every year to studying the evolution of everything from molecules to Mars so it is unsurprising they are unwilling to attempt to anything that might have to do with creation science.  However, this idea of Scherer’s can be tested.  Fertilization can be performed in the lab and the cells brought forward in the development process. Unlike humans, animal gametes can be combined, and the results disposed of after the completion of the experiment without any ethical implications or sin.  It would be nice to see some creation scientists testing this. I would expect that the cells would not be able to develop for more than a short period of time, perhaps a week or two in larger mammals, less in smaller creatures with shorter gestation or nesting times.

Wood and Murray discuss this hybridization problem in detail in their 2003 book.  Because of the problem of what makes a hybrid successful, along with the impossibility of using hybrid data on fossils, they reject hybridization as the gold standard, though they do regard it as valuable[30].  We have already discussed the numerous problems with their statistical methodology they proposed in place of hybridization, but is hybridization any better in light of the difficulties we have in defining its success?

The answer is a resounding yes, not because of what I say, but because of what the Bible says. Recall from article one that the Bible defined the kind as a reproductive grouping.  Thus, kinds were able to reproduce together in the beginning. This is God’s standard of a kind, not a man’s. Thus, referring to it as the gold standard is not a stretch at all. In fact, Wood’s attempt at a holistic approach is in opposition to the way the Bible defines the kind. I admire his attempt to approach the kind scientifically, but he has missed the point. From a natural scientific view, it is impossible to correctly understand the Biblical kind, because the kind was created supernaturally.  Once that is accepted presuppositionally, then the rest of the data falls into place, including hybridization[31].

Based on Scherer’s definition of hybridization success, what can we infer from observation of the natural world? Obviously, every mating attempt we observe cannot be traced to conclusion.  We cannot perform daily ultrasounds on a female animal in the wild to determine if fertilization is successful, or how far the fertilized egg develops.   Further, some creatures have complicated mating displays and dances where if one partner makes a false step, courtship ends[32][33].   In addition, some members of the same baramin will now prey on each other if given the chance. Any one of these cases could prevent members of the same kind from attempting to hybridize. This is why we desperately need laboratory embryogenesis studies on creatures suspected to be of the same created kind, but for which no hybridization data exists.

How then do we deal with these objections? The only way to deal with the impossibility of tracking reproductive activities in the wild is to perform the tests in the lab ourselves. However, the resources of creation scientists are stretched incredibly thin. Most double as full-time college professors and speakers, or dedicated writers, researchers and speakers and do not have the time or the facilities to perform this kind of research.  This situation needs to change if this work is to be performed. For it to change, we desperately need more creation scientists of all descriptions, but particularly in astronomy, paleontology, chemistry, zoology and botany.  Of course, lack of time is not an excuse and it would be good to see the few creation friendly universities to institute these kinds of programs.

Mating displays are troublesome, but not insurmountable.  The same mechanism can be employed to get around them. It is also not impossible at all for the creation model that species-specific mating displays could develop in the years after the flood. Creatures would have speciated rapidly after the flood and, as they spread from Ararat and became reproductively isolated, they would have adapted their behavior to fit their environment. This would have permitted the development of species-specific mating behavior.

Further evidence for this comes from the fact that at least some animals have the ability to alter their mating behavior to fit changes in their environment. Fiddler crabs, for example, will alter their mating and courtship in response to the presence of a predator[34]. Guppy males will alter their approach to winning a mate if there is a nearby predator[35].  Some moths do this as well[36]. These are just a few examples of animals altering their mating display in the presence of a predator and they do it intuitively.  Every member of the species does it automatically and is able to recognize the counterpart display in members of the same species.

This, however, does not explain why two members of different species interbreed. There could be a couple of natural reasons for this. The lack of a suitable mate is perhaps the most obvious reason but there are others. Unlike conscious humans who have the conscious ability to act against their natural urges, animals act solely on instinct. The urge to breed is strong in animals innately. This makes sense, given God made them in the beginning to fill the earth[37].  In order to do so, they would have needed to interbreed. Thus, an urge to do so makes perfect sense. Further, sensory failure could also be invoked as a mechanism for interbreeding.

Lack of a suitable mate is a legitimate hybridization reason. For example, there are three species of zebra found in Africa. Grevy’s zebra is fairly rare, with a small range in Kenya and Ethiopia. The plains zebra is much more abundant. However, where the ranges overlap, they freely interbreed[38]. Since zebra species are very similar to look at, it would not be surprising that the two interbreed. However, researchers do not postulate this as the reason. Instead, they propose that, because Grevy’s zebra has such a small population, it is willing to interbreed with something similar.  However, this is a hypothesis at best and has yet to be proven.

The breeding urge is perhaps the driver behind numerous particularly strange interspecific mating attempts. Such is the case in breeding attempts between sea otters and harbor seals. Were offspring to result from this mating, it would be the aforementioned “true hybrid”, i.e. the result of mating between two separate kinds. However, what generally occurs is a large, male otter attacks a juvenile female seal and forcibly attempts to breed with her, often killing her in the process[39]. This only makes sense if the urge to breed is overriding all other concerns in these males.  As noted above, the breeding urge is very strong. If no suitable females are available, then these males seem to be willing to breed with anything that resembles a suitable female.

However, in most cases, scientists are unable to explain why hybridization occurs. They toss out a lot of postulations, but generally are unable to come up with a solid answer. For example, in Spain, brown trout freely hybridize with Atlantic salmon, but scientists do not know why[40]. A study of reef wrasses came to the same conclusion. They proposed several different possibilities but did not nail it down to a final conclusion[41]. Numerous bird hybrids have the same issues[42].

In essence, evolutionists are attempting to reconcile two, irreconcilable concepts.  Their model requires that distinct species form. Their model also further demands that these species breed with each other and produce hybrids. These hybrids must be equally fit or perhaps more fit to their environment as their parent species. These hybrids must further be able to form new species with their own distinct genetic patterns. Yet because of their belief in natural selection, the vast majority of these hybrids must be unfit and die off.  As Coyne and Orr point out “Darwin realized that he asked his readers to believe both that most evolution is due to natural selection and that this evolution routinely yields species that produce unfit hybrids.[43]

While evolutionists attempt to force natural selection and hybridization to work together, it ignores the logical question of, should hybridization even occur if species are real? Evolutionary ideology seems to indicate the answer is no. “If they (populations) meet and overlap with no, or only the rarest, hybridization, then there is no doubt that they are behaving like good species.[44]”.  in other words, two species should not hybridize or only do so rarely for evolutionary taxonomy to work. As we have seen, this is not the case.  Hybridization only works if the species is an arbitrary grouping under a larger heading, between which no hybridization is possible.

This places evolution in a very difficult position.  If the species concept is real, then hybridization should not occur. Yet hybridization is what they believe helps form new species. Without hybridization, new species can form but are a net loss of information and thus do not progress evolution. Thus this is unacceptable to the evolutionist. If, however, the species concept is arbitrary, then speciation is equally arbitrary. This is equally catastrophic to evolution, because, as Mayr pointed out “And speciation, the production of new gene complexes capable of ecological shifts, is the method by which evolution advances.  Without speciation, there would be no diversification of the organic world, no adaptive radiation, and very little evolutionary progress.[45]” Thus the evolutionists are trying to have it both ways. They want speciation to be the mechanism of evolution, and hybridization to work simultaneously.  Hybridization or mixta does occur, but if the species concept is real, it should not. Yet if the species concept is not real, then evolution is dead.  They want to have both, but logically, this is impossible.

Creation and Hybridization

From a creation perspective, hybridization, the mixta concept works perfectly well. That hybrids appear and frequently thrive is no surprise to a person acquainted with the Biblical account of creation. In fact, in view of the original created kind, hybridization is expected to occur, and occur regularly, particularly in the post-fall and post-flood world. In both cases, a small population of animals was able to quickly diversify.  This would have happened as members of the same kind freely interbred, forming what evolutionists would call hybrids. As these hybrid populations spread out from one another, their available genetic information decreased. This led to certain traits becoming fixed, such as stripes in a zebra, or manes in male lions.  A fixed trait is a trait that does not vary largely within a population. While the exact pattern of zebra stripes and the size and color of a lion mane vary by the individual, zebras have stripes and male lions have manes, almost without exception.

Creationists recognize that hybridization is a factor in the speciation process[46]. Other than polyploidy, hybridization would have been the biggest contributor to early post-flood speciation.  However, after a few decades, hybridization would have become less frequent as animal populations spread and filled the earth. At that point, allele frequencies would have become fixed in many populations. Since there is no known process by which new information can arise in a genome, new species can arise one of three ways in the current world. Polyploid speciation, discussed previously, is instant but no new information is added to the genome.  Further reproductive isolation of a sub-population actually decreases the amount of information in the genome and results in even less variation.  Only mixta, the hybridization process, increases the available genetic information in the new species.  Thus hybridization seems the most valuable way to create a new species.

However, creating a new species is not enough for evolution. Evolution requires that whole new basic types are formed, not just new species.  They simply regard speciation as their mechanism. As we have demonstrated in this chapter, this is impossible. While speciation, by hybridization and other mechanisms does happen, it is not “synonymous with evolution” as Simpson claimed.

Conclusions

 Hybridization is a very interesting idea. However, true hybridization does not occur. Instead what we observe is mixta, breeding within a higher grouping: the baramin.  Hybridization does present it’s problems for the baramin concept, given the difficulty in defining its success or failure. It is likely even Scherer’s definition is not completely accurate and will need to be adjusted as more data becomes available. However, hybridization presents a far larger problem for the evolutionist than it does the creationist.  Hybridization should not happen in the evolutionary worldview, or at least not often. Certainly not often enough to produce new species, yet it does. This creates a problem for evolutionists. Either their dogma fails the hybridization test or it fails on speciation. They cannot have it both ways.  As such, the creation model works far better as an explanation for hybridization.

 

References

[1] Mayr, 1965

[2] Coyne and Orr, 2004.

[3] Meyer et al, 2006.

[4] Loren Rieseberg “Hybrid Origins of Plant Species” Annual Review of Ecology and Systematics Volume 28 (1997) Pages 359-389. https://pdfs.semanticscholar.org/1daf/ae0eaa3cd62772689eefa392ea855cad1985.pdf

[5] Mallet, 2007.

[6] Coyne and Orr, 2004.

[7] Simpson, 1961.

[8] Coyne and Orr, 2004.

[9] M.S.Y. Lee “Species concepts and species reality: salvaging a Linnaean rank.” Journal of Evolutionary Biology Volume 16 (2003) Pages 179-188. https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1420-9101.2003.00520.x

[10] Simpson, 1961.

[11] Benjamin H. Burma “Reality, Existence and Classification: A Discussion of the Species Problem.” Madrono Volume 12, No. 7 (1954) Pages 193-209. https://www.jstor.org/stable/41422819?read-now=1&seq=17#page_scan_tab_contents

[12] Aelys M. Humphreys and Timothy G. Barraclough. “The evolutionary reality of higher taxa in mammals.” Proceedings of the Royal Society B Volume 281, No. 1783 (2014) Pages 1-10. https://royalsocietypublishing.org/doi/pdf/10.1098/rspb.2013.2750

[13] Panchen, 1992.

[14] A.J. Cain Animal Species and Their Evolution Princeton: Princeton University Press, 1954.

[15] Lightner, 2012.

[16] James Cahill, Ian Stirling, Logan Kistler, Rauf Salamzade, Erik Ersmark, Tara L. Fulton, Mathias Stiller, Richard Green, and Beth Shapiro. “Genomic evidence of geographically widespread effect of gene flow from polar bears into brown bears.” Molecular Ecology Volume 24, No. 6 (2015) Pages 1205-1217. https://onlinelibrary.wiley.com/doi/pdf/10.1111/mec.13038

[17] Jodie D. Pongracz, David Paetkau, Marsha Branigan, and Evan Richardson. “Recent Hybridization between a Polar Bear and Grizzly Bears in the Canadian Arctic.” Arctic Volume 70, No. 2 (2017) Pages 151-160. https://www.researchgate.net/profile/Evan_Richardson2/publication/317271906_Recent_Hybridization_between_a_Polar_Bear_and_Grizzly_Bears_in_the_Canadian_Arctic/links/5936e4224585158f6448288e/Recent-Hybridization-between-a-Polar-Bear-and-Grizzly-Bears-in-the-Canadian-Arctic.pdf

[18] Rodney S. Nairn, Donald C. Morizot, Steven Kazianis, Avril D. Woodhead, and Richard B. Setlow. “Nonmammalian Models for Sunlight Carcinogenesis: Genetic Analysis of Melanoma Formation in Xiphophorus Hybrid Fish.” Photochemistry and Photobiology Volume 64, No. 3 (1996) Pages 440-448. https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1751-1097.1996.tb03089.x

[19] Gil G. Rosenthal, Xochitl F. De La Rosa Reyna, Steven Kazianis, Matthew J. Stepehens, Donald C. Morizot, Michael J. Ryan, and Francisco J. Garcia de Leon. “Dissolution of Sexual Signal Complexes in a Hybrid Zone between the Swordtails Xiphophorus birchmanni and Xiphophorus malinche (Poeciliidae).” Copeia Volume 2 (2003) Pages 299-307. http://www.sbs.utexas.edu/ryan/Publications/2003/2003Copeia2-299.pdf

[20] Ji Hyoun Kang, Manfred Schartl, Ronald B. Walter, and Axel Meyer. “Comprehensive phylogenetic analysis of all species of swordtails and platies (Pisces: Genus Xiphophorus) uncovers a hybrid origin of a swordtail fish, Xiphophorus monticolus, and demonstrates that the sexually selected sword originated in the ancient lineage of the genus but was lost again secondarily.” BMC Evolutionary Biology Volume 13, No. 25 (2013) https://bmcevolbiol.biomedcentral.com/articles/10.1186/1471-2148-13-25

[21] Marsh, 1976

[22] Niklas, 1997.

[23] John A. Endler. “Integrative commentary on ecology and evolution of poeciliid fishes” in Ecology and evolution of poeciliid fishes, (University of Chicago Press, Chicago, Ill., 2011.) http://dro.deakin.edu.au/eserv/DU:30043181/endler-integrative-2011.pdf

[24] Susanne Schories, Manfred K. Meyer, and Manfred Schartl. “Description of Poecilia (Acanthophacelus) obscura n. sp., (Teleosti: Poeciliidae), a new guppy species from western Trinidad with remarks on P. wingei and the status of the “Endlers Guppy”.” Zootaxa Volume 2266 (2009) Pages 35-50. https://www.mapress.com/zootaxa/2009/f/zt02266p050.pdf

[25] Marsh, 1976.

[26]Van Someren et al, 1974

[27] C.A Kozak, J.B. Lawrence, and F.H Ruddle. “A sequential staining technique for the chromosomal analysis of interspecific mouse/hamster and mouse/human somatic cell hybrids.” Experimental Cell Research Volume 105 No.1 (1977) Pages 109-117. https://www.sciencedirect.com/science/article/pii/0014482777901562

[28] Genesis 1:27

[29] Siegfried Scherer “Basic Types of Life.” In Mere Creation ed William Dembski (Downers Grove, IL: InterVarsity Press, 1998.

[30] Wood and Murray, 2003.

[31] For a more thorough discussion of why presuppositions are necessary and why everyone makes them see Lisle, 2009.

[32] Sarah C. Humfeld. “Condition-dependent signaling and adoption of mating tactics in an amphibian with energetic displays.” Behavioral Ecology Volume 24, No.4 (2013) Pages 859-870. https://academic.oup.com/beheco/article/24/4/859/220157

[33] Lynne D. Houck and Stevan J. Arnold. “Courtship and Mating Behavior.” In Reproductive Biology and Phylogeny of Urodela ed David M. Sever.  (Enfield, New Hampshire: Science Publishers, Inc. , 2003.

[34] Tsunenori Koga, Patricia R.Y. Backwell, Michael D. Jennions and John H. Christy. “Elevated predation risk changes mating behavior and courtship in a fiddler crab.” Proceedings of the Royal Society of London B Volume 265 (1998) Pages 1385-1390. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1689227/pdf/BP30GHKV9FW4BK09_265_1385.pdf

[35] J. Godin. “Predation risk and alternative mating tactics in male Trinidadian guppies (Poecilia reticulata).” Oecologia Volume 103 (1995) Pages 224-229. https://www.researchgate.net/profile/Jean-Guy_Godin/publication/226670161_Predation_risk_and_alternative_mating_tactics_in_male_Trinidadian_Guppies_Poecilia_reticulata/links/54328b940cf22395f29c2293/Predation-risk-and-alternative-mating-tactics-in-male-Trinidadian-Guppies-Poecilia-reticulata.pdf

[36] Gareth Jones, Anna Barabas, Wendy Elliott, and Stuart Parsons. “Female greater wax moths reduce sexual display behavior in relation to the potential risk of predation by echolocating bats.” Behavioral Ecology Volume 13, No. 3 (2002) Pages 375-380. https://academic.oup.com/beheco/article/13/3/375/221863

[37] Genesis 1:28

[38] J.E. Cordingley, S.R. Sundaresan, I.R. Fischhoff, B. Shapiro, J. Ruskey, and D.I. Rubenstein. “Is the endangered Grevy’s zebra threatened by hybridization?” Animal Conservation Volume 12 (2009) Pages 505-513. https://zslpublications.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-1795.2009.00294.x

[39] Heather S. Harris, Stori C. Oates, Michelle M. Staedler, M. Tim Tinker, David A. Jessup, James T. Harvey, and Melissa A. Miller. “Lesions and Behavior Associated with Forced Copulation of Juvenile Pacific Harbor Seals (Phoca vitulina richardsi) by Southern Sea Otters (Enhydra lutris nereis).” Aquatic Mammals Volume 36, No.4 (2010) Pages 331-341. https://werc.ucsc.edu/Publications/2010%20Harris%20et%20al.pdf

[40] C. Garcia de Leaniz and E. Verspoor. “Natural Hybridization between Atlantic Salmon, Salmo salar and brown trout, Salmo trutta, in northern Spain.” Journal of Fish Biology Volume 34 (1989) Pages 41-46. https://s3.amazonaws.com/academia.edu.documents/32999628/hibrido_salar_trutta.pdf?AWSAccessKeyId=AKIAIWOWYYGZ2Y53UL3A&Expires=1545086756&Signature=o2wCu5IwRD11k4jqPwvZZVRdRIg%3D&response-content-disposition=inline%3B%20filename%3DHibrido_salar_trutta.pdf

[41]Siti M. Yaakub, David R. Bellwood, Lynne van Herwerden and Fenton M. Walsh. “Hybridization in coral reef fishes: introgression and bi-directional gene exchange in Thalassoma (family Labridae).” Molecular Phylogenetics and Evolution Volume 40 (2006) Pages 84-100. https://pdfs.semanticscholar.org/8e9d/98d079eed5fdbfb045a81085197899d05ecc.pdf

[42] Eugene M. McCarthy Handbook of Avian Hybrids of the World (Oxford: Oxford University Press, 2006)

[43] Coyne and Orr, 2004

[44] Cain, 1954.

[45] Mayr, 1965.

[46] Jean Lightner. “Towards a creationary view of why speciation occurs.” Journal of Creation Volume 30, No. 1 (2016) Pages 70-75. https://creation.com/images/pdfs/tj/j30_1/j30_1_70-75.pdf

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