Pesky Details: Essays for "Left Brain" Christians by Bob Knight Barsch
Chapter IX - Hybridism
The view commonly entertained by naturalists is that species when intercrossed, have been specifically endowed with degrees of sterility, in order to prevent their confusion (Page 263).
Darwin noted that this statement "seems at first highly probable..." (Page 263). His view was that natural selection working on variation was not responsible for the inability of related but different species to produce infertile offspring. Secondly, Darwin also acknowledged that the crossing of different species also can fail to produce any offspring. He felt it was important to recognize that there is a difference in crossing different species that produce infertile hybrids and those crosses that produce no offspring. He also said that varieties within the species produce offspring that are fertile.
Critique
This subject leaves little for fruitful discussion. Different species by definition do not, generally, interbreed and if they do, they do not produce offspring, but if they do produce offspring, the offspring are infertile. A species is a group of organisms that successfully interbreeds and produces fertile offspring. All else is speculation.
Darwin's speculation in this discussion was that God did not make separate species because cross-breeding closely related species results in varying degrees of sterility. If degrees of sterility show degrees of relatedness between different species, God could not have been involved in the creation of new species. If species give rise to sister species, God had nothing to do with the appearance of species. In the case of domestic varieties of pigeons, God could not have made wild pigeons because man derived varieties of the species from wild birds. Perhaps Darwin's studies of theology while at Christ College, Cambridge, from 1827 -1831 provided him with special insights on God's limits?
Degrees of Sterility
Discussion of this topic included experiments and observations of horticulturalists. Horticulturalists Kolreuter and Gartner, "two conscientious and admirable observers" (page 264) after devoting their lives to their experiments and findings, derived contradictory conclusions. Kolreuter observed that crossing different varieties and species of plants produced set degrees of productivity and sterility. By contrast, Gartner noted varying degrees of sterility or productivity over time with continued, controlled pollination experiments. Darwin disagreed with Gartner:
...an occasional cross with a distinct individual or variety increases the vigor and fertility of the offspring, and on the other hand ... a very close interbreeding lessens their vigour and fertility... (Page 265) and....some degree of sterility between distinct species is a universal law of nature (Page 266).
Following the discussion of inter-species and inter-variety breeding of plants, Darwin talked about relative sterility among animal crossings. He noted that the crossing of species of animals was more likely to produce no offspring or sterile offspring than was the crossing of plant species. An example of successful interspecies cross breeding was that of the hare and the rabbit:
It has lately been asserted that two such distinct species as the hare and rabbit, when they can be got to breed together, produce offspring, which are highly fertile when crossed with one of the parent-species (Page 268)... and...With our domesticated animals, the various races when crossed together are quite fertile; yet in many cases they are descended from two or more wild species (Page 268).
Darwin believed, for example, that domestic dogs and domestic cattle resulted from the crossing of multiple species of wild canine and bovine species, respectively.
Critique
Again, Darwin failed to say how the cross-breeding of plant "species" and varieties or his "evidence" on the derivation of domestic animals related to his theory of the gradual evolution of all species from a single ancestor species. Perhaps his "evidence" illustrated the general plasticity of and connectivity of species and their inherent ability to develop into other forms or other species without divine interference?
Can one crossbreed the cottontail and the jackrabbit and produce viable offspring? Did the domestic dog derive from different species, as Darwin claimed, or does the domestic dog merely represent the genetic potential of the one wolf species Canis lupis? How sound were Darwin's observations and anecdotal evidence?
As noted above, we must conclude that Darwin had special insights from his observations and those of others. The variation in degrees of sterility among inter-species crossings proved to Darwin that God did not produce species. A cross between a donkey and a horse produces a mule and therefore God had nothing to do with the appearance of the horse nor donkey and therefore all species evolved naturally from a common 1-celled organism?
Laws Governing the Sterility of First Crosses and of Hybrids
In this case, Darwin addressed the concept suggested by typologists/taxonomists that the purpose of sterility was to maintain species identity. He noted that typologists had classified species on the basis of their "systematic affinity," that is, according to their similarity in structure. In general, Darwin agreed with the typologists in their classification schemes, but he pointed out that degrees of sterility resulted from crossing plants of different species. That is, varying degrees of sterility indicated varying degrees of connectivity and therefore varying distance from common ancestry.
Crossing of plant species from different families inevitably produced no seed, crossings between species of the same genus produced sometimes no seed and sometimes viable seed in varying amounts. Crossings of varieties within a species produced viable seed and often abundant seed as a result of hybrid vigor. Similar degrees of sterility occurred in the crossing of animal species and varieties. Generally, the closer plants and animals were related in their classification by typologists, the more likely they were to consistently produce viable offspring.
Because of the large amount of variation in degrees of sterility among the crossings of widely separated and closely related species, as classified by the typologists, Darwin concluded:
Now do these complex and singular rules indicate that species have been endowed with sterility simply to prevent their becoming confounded in nature? I think not. For why should the sterility be so extremely different in degree, when various species are crossed, all of which we must suppose it would be equally important to keep from blending together (Page 273).
Critique
If two different organisms freely breed or cross-pollinate and produce viable offspring that survive in the wild, the two organisms are classified as the same species. If two species when crossed do not produce offspring, these organisms are classified as different species. If two different species produce sterile offspring in the wild, the two species are closely related but different species. One could say that relatedness among different classifications of plants and animals suggests the possibility of common descent and one could argue with a degree of probability that species, as programmed, derived rapidly from sister species (the fossil record shows no intermediate, evolutionary steps).
The non-Darwinian and mysterious development of some 300 endemic species of fish from a handful of cichlid species in Lake Victoria, Africa over the last 12,400 carbon-14 years is a good example of rapid speciation from a few founders (Johnson et al. 1996). Such rapid speciation without isolation is not Darwinian nor "allopatric" as proposed by Eldridge and Gould (1972). See "Allopatric speciation" under Definitions/Notes at the end of this essay.
I suggest that the claim by Darwin's opponents that the degree of sterility was God's way of preserving species identity was correct. We note in the Mosaic Law (Leviticus 19:19a) that God forbid the cross breeding of different kinds of animals: "You shall keep my statues. You shall not let your animals breed with a different kind..." Perhaps this scripture represented God's desire to preserve the genetic integrity of engineered "kinds" of organisms? The story of Noah's ark (Genesis 6-9) also testifies to God's desire to preserve species diversity.
In like manner, contemporary biologists take measures to preserve species integrity. Biologists today frequen
Origin and Causes of the Sterility of First Crosses and of Hybrids
Darwin stated:
...the sterility of first crosses and hybrids might have been acquired through the natural selection of slightly lessened degrees of fertility...for ...it would clearly be advantageous to two varieties or incipient species, if they could be kept from blending... (Page 275).
The problem of natural selection producing degrees of sterility arises in the process of passing that character from parent to offspring, when crosses produce fewer and fewer offspring to carry on the character of decreased sterility. Darwin concluded:
...it would be superfluous to discuss this question in detail; for with plants we have conclusive evidence that the sterility of crossed species must be due to some principle, quite independent of natural selection (Page 276).
Next, Darwin discussed the causative agents in plants of sterility in first crosses and hybrids. In some cases:
...the male element fails to reach the ovule, as would be the case with a plant having a pistil too long for the pollen-tubes to reach the ovarium...Again, the male element may reach the female element but be incapable of causing an embryo to be developed... and... Lastly, an embryo may be developed and then perish at an early period (Page 277).
Darwin observed that some wild animals, for example, the elephant, fail to breed in captivity. He believed that "change in the external conditions" were responsible for this form of sterility.
Darwin did say that hybrids of two different species may fail to reproduce because "the reproductive system, independently of the state of health, is affected..." For example the cross between a horse and a donkey can produce a sterile yet healthy mule. Inbreeding of hybrids can mask the effects of cross-breeding between species but breeding of varieties within the same species can produce hybrid vigor. Darwin finalized this section with a comment on "the principle of life" that apparently addressed the phenomenon of hybrid vigor:
...according to Mr. Herbert Spencer, being that life depends on, or consists in, the incessant action and reaction of various forces, which, as throughout nature, are always tending towards an equilibrium; and when this tendency is slightly disturbed by any change, the vital forces gain in power (Page 280).
Critique
Darwin did not, once again, make much of an effort to tie his discussion on the sterility of first crosses and hybrids to his special theory of natural selection (a microevolutionary process) nor to his general theory of macroevolution. He did posit that degrees of sterility indicated degrees of relatedness, suggesting common descent and relative distances from common ancestry. In Darwin's mind, God could not have produced various kinds of organisms if species or varieties derived from other species.
Reciprocal Dimorphism and Trimorphism
Darwin believed that some species of plants produced two or three different forms. Individual plants in the same species would look alike in structure but the sexual parts would differ. The flowers of one form had elongated stamens and a relatively short pistil, a second form had elongated pistil and short stamens, and a third form might have stamens and pistil of equal length. Artificial pollination among the three forms within the same species of plant produced varying amounts of sterility, dwarfism, and vigor. Crossings of forms within the species that produced sterility or dwarfism, Darwin called "illegitimate". Crossings between species that produced sterility, reduced fertility, or dwarfism, he labeled as "hybrid".
Critique
Numerous species produce abundant variation through their offspring. This variation in body form or polymorphism enables species to adjust to different or changing environmental conditions. Some species may produce fewer offspring than other varieties of the same species. Generally, species with lower rates of reproduction experience higher rates of individual survivability and those species that have high rates of reproduction also have high mortality rates. Thus, total numbers of offspring produced may not indicate degree of relatedness among varieties or between species. When Darwin's cross-pollination experiments failed to produce offspring, he obviously attempted to cross-pollinate different species.
Darwin classed crossings that produced no offspring "illegitimate" and "hybrid" if the crossing produced sterile or dwarfed offspring. Thus, species crossings that produced no offspring indicated less relatedness between the parents than did crossings that produced sterile or deformed offspring. Our observations that the offspring of a horse crossed with a donkey produces a sterile mule and the artificial insemination of a feline species with sperm from a canine species produces no offspring are not surprising. Horses and donkeys are related species of organisms, cats and dogs less so.
But the root of the problem for Darwinian evolution is not in the relatedness of species, but the inexplicable origins of biological information required to produce species differences. Neo-Darwinism is unable to account for speciation events because any change in the production of functional molecules requires changes in biological information. The neo-Darwin mechanism of random mutation cannot produce new functional molecules because:
... (1) it has no means of efficiently searching combinatorial sequence space for functional genes and proteins and, consequently, (2) it requires unrealistically long waiting times to generate even a single new gene or protein. It has also shown that the mechanism cannot produce new body plans because; (3) early acting mutations, the only kind capable of generating large-scale changes, are also invariably deleterious, and (4) genetic mutations cannot, in any case, generate the epigenetic information necessary to build a body plan (Meyer 2013:411).
Fertility of Varieties when Crossed, and of their Mongrel Offspring, not Universal
By definition, varieties within a species are of the same species because crosses among them produce fertile offspring. However, under domestication, for example, some varieties within a species produce more offspring than others. Thus, a person who classifies "species" based on relative fertility among individuals, may conclude that two varieties, one of which produces few offspring and another that produces numerous offspring are different species.
Critique
If two individuals when crossed produce fertile offspring that survive in a wild state, they are by definition the same species. As stated under Critique, Reciprocal Dimorphism and Trimorphism, above, the production of varying numbers of offspring may reflect the relative survivability of individuals in the species, another case of variation within the species boundary that can assure species survival under new or changing environmental conditions. Relative sterility among varieties of the same species does not necessarily reflect degree of relatedness and certainly provides no evidence that all organisms derived from a common ancestor.
By contrast, occasionally, closely related but "different species" breed in the wild and produce fertile offspring. For example, genetic studies indicate that the red wolf (Canis rufus) of the southeast United States is a cross between the gray wolf (Canis lupus) and the coyote (Canus latrans). Darwin made no attempt to incorporate his specific theory of natural selection nor his general theory of the gradual evolution of species into new species into his discussion of the varying fertility among varieties. His point in these discussions was that God did not individually create the parent stock because man artificially produced classifications such as "hybrids" and "mongrels" through cross-breeding. In addition, degrees of sterility showed relative relatedness of organisms on the evolutionary tree of life, illustrating that God was never involved in speciation.
Hybrids and Mongrels Compared, Independently of their Fertility
Independently of the question of fertility, the offspring of species and of varieties
Darwin quantified "the question of fertility" by counting the varying numbers of seeds produced as a result of crossing two different species of plants or two varieties of plants. In this discussion, Darwin referred to experiments by several colleagues, all of whom produced varying results in comparing the offspring of crosses between two distinct species and the offspring of crosses between varieties within the same species. For example, the offspring of a cross between two different species produced hybrids that were observed to show less variation of form than the offspring of a cross between two varieties (mongrels) within the same species. And, "hybrids between very closely allied species are more variable than those from very distinct species..." (Page 287). Darwin pointed out that this rule of crosses between closer related individuals producing more variation in the offspring was obvious in the production of domesticated plants and animals that show a lot of variant forms.
He observed that the causes of variability in domestic species resulted from "the reproductive system being eminently sensitive to changed conditions of life" (Page 288). That is, plants and animals taken from the wild and placed into the new conditions of domestication will produce more variation in their offspring than the parent species did in the wild. Of interest, Darwin also believed that domestic plants and animals were the hybrids of numerous distinct species in the wild. These different species when crossed to produce domestic plants and animals:
...are descended from species (excluding those long-cultivated) which have not had their reproductive systems in any way affected, and they are not variable; but hybrids themselves have their reproductive systems seriously affected, and their descendants are highly variable (page 288).
Darwin concluded:
Independently of the question of fertility and sterility, in all other respects there seems to be a general and close similarity in the offspring of crossed species, and of crossed varieties. If we look at species as having been specially created, and at varieties as having been produced by secondary laws, this similarity would be an astonishing fact. But it harmonises perfectly with the view that there is no essential distinction between species and varieties (Page 290).
Critique
Darwin was correct in his final statement for this section that "there is no essential distinction between species and varieties" (Page 290). That is, he was correct if he meant to say that varieties of the same species are the same species. All dogs are of the same species as wild wolves, for example, but though the same species, varieties of dogs are often different in structure, size, and behavior. Thus, "species" and "variety" are valid and useful classifications.
Darwin switched from theoretical and historical scientist to theologian in his statement:
If we look at species as having been specifically created, and at varieties has having been produced by secondary laws, this similarity would be an astonishing fact (Page 290).
Perhaps Darwin meant that the similarity among varieties of the same species could not have microevolved from a species that God created? Perhaps he was saying that God would not have programmed a species to produce varieties nor sister species which were, in his mind, the result of the laws of nature and chance events? What did he mean by "this similarity"...that varieties in the same species are similar in structure or that more closely related varieties, as among closely related species, when crossed produce greater variation on their offspring than do crosses among more distinct forms? Darwin did believe that varieties were "incipient species" and that all species were therefore at one time evolving varieties from a parent species. Thus in a discussion of varieties and species, his goal was to say that one does not differ from the other and that both are plastic and in a constant state of flux and evolution toward new species.
Darwin's specific theory of microevolution through the power of natural selection and his general theory of the macroevolution of all organisms from a common ancestor are easy to understand. By contrast, the specific "evidences" he used to support his general theory were often obscure and based on anecdotal observations, tautological reasoning, and obscure relationships with numerous possible explanations. I suggest that the popularity of his writing hinged upon the popularity of his general philosophy of the materialistic evolution of organisms, not on the clarity and power of his reasoning at the evidential level.