The Genetics of SpeciesJune 9, 2007
As part of the Biochemistry degree that I was working on when I first came to college I took a class simply entitled Evolution. The class was actually more about population genetics than specific evolutionary lineages of species. There are a surprising number of equations based on population genetics and most of what I know about mutation and population genetics I owe to that class.
The reason I mention this is because it was in this class that I came to the full realization that what we call “species” is an entirely human construction that we have forced upon nature. Species do not really exist in nature in the strictest sense in which we portray them.
Definitions of Species
Allow me to explain. The popular definition of species currently used is what is called the “Biological definition of species” which defines a species as a group of organisms which can interbreed with each other and produce fertile offspring. The fact that we have to specify ‘fertile’ is the first clue. Most every *cough* knows that you can breed a horse and a donkey to get a mule. Mules are almost always sterile so donkeys and horses are considered different species.
The boundaries we have set up break down even more when you consider “ring species“. These are a very interesting phenomena where a group of similar animals are spread out in a ring because of a physical feature (like a mountain). The animals can breed with each other in adjacent areas and genes can be passed clockwise around a mountain showing gradual change the whole time until the circle is complete and the group that results can no long breed with the starting population. So is it one species, two, or maybe seven?
It should be of interest that the Bible never uses the word ‘species’ as it is clearly a human definition. In Genesis chapter 1 the Bible instead refers to animal “kinds” 10 times in 13 verses. Looking at it now, it almost seems as if the author is over emphasizing the point, being emphatically repetitively redundant. “God made the wild animals according to their kinds, the livestock according to their kinds, and all the creatures that move along the ground according to their kinds.” Genesis 1:25. God apparently created the original, whole and perfect kinds as a more variable, adaptable category of animals than what we have today. Kinds is certainly broader than species and wherever we see two species able to interbreed and create a hybrid, that is evidence they are, in fact, the same kind. The modern founder of taxonomy, Carolus Linnaeous, was actually a devout Christian and it appears in many cases that genus is the closest thing to the Biblical kind. Thus we say genus first, then species (specialization) second. This practice goes back to ancient times.
Baraminology is an alternative method of classification based on the study of Biblical “kinds” called baramins. The field is based upon the Bible’s statement that God created animals according to their kind and that they would reproduce according to their kind. The study of baramins is laid out in Todd Wood’s “Undertanding the Pattern of Life”, which is a fairly straight forward overview designed as a textbook on the subject. Baraminology is still a fairly new area of study. It incorporates both evidence of continuity as well as evidence of discontinuity. It is like no other system before it; Linnaeous believed in species fixity most of his life, and evolutionist believe any evidence of discontinuity is only a lack of data.
Answers in Genesis has a good explanation of the contrast between species models. The ability of two organisms to breed with each other and produce offspring is used as evidence of continuity; they are part of the same kind. Evidence of holistic differences between groups of organisms, like turtles as compared with all other reptiles, is used as evidence of discontinuity. So turtles and geckos never shared a common ancestor, but Asian and African elephants, along with woolly mammoth probably did share an ancestor. Didn’t know we had mammoth DNA? Baraminology is useful as a diverse classification system and in understanding the pattern of life in a creationist worldview.
Almost every ancient culture on the planet has a story of a worldwide flood. The Gilgamesh Epic is often quoted as an example but it is only one of 200 documented flood stories. The fact that this story is so widespread across cultures with no contact lends credence to the idea that it actually happened. The Biblical account is (to my knowledge) the most detailed account so I will use that account here. The story goes that in order to preserve all the animals as well as mankind against a worldwide flood, a chosen person (Noah, Manu, etc.) built a giant life raft, called an Ark. Noah crammed all the animals onto the Ark, and these sole survivors were responsible for repopulating the entire planet afterwards. Let’s take a look at the feasibility of the species scenario laid out in the Bible from a genetics point of view.
So in the Biblical scenario the Ark comes to a rest at Mount Ararat, at the intersection of three major continents. The plants and plant seeds that have survived the Flood (along with insects and fish) are already dispersed throughout the planet while all the animals are concentrated in one place. The natural thing to do as an animal at this point is spread and reproduce like crazy. Our normal ecological models are based around an assumption of competition for limited resources of food and land. Each one of these animal kinds (baramins) is originally genetically diverse but each new population of animals is started from only a few individuals. This means that that genetic diversity will be subdivided, then subdivided, and subdivided again. This would create a lot of genetic drift and loss of genetic diversity inside each sub-group. Keep in mind that there is no new genetic information being added to the population but instead a loss of genetic information creates increasingly distinct biological groups over a very short period of time. This comes at a cost to fitness so that this process cannot go on forever.
Some would call this rapid speciation even evolution, in which case, not only do creationists believe in evolution, they believe in a far faster form of evolution than even Richard Dawkins could stomach. However, it is probably more accurate to call this adaptation or even genetic degradation. The nature of ‘new genetic information being added to the genome’ versus ‘genetic information being lost’ is fundamentally different. New information entering the genome is a process that would take millions of years, (if not an infinite amount of time), and so cannot really be observed inside a human time frame. Since it cannot be observed it is hard to call it science. Loss of genetic information, on the other hand, can happen in a single generation, and is scientifically testable and provable.
Hybrids are an important piece of evidence for baraminology. There are actually far more hybrids than I ever imagined. Generally, hybridization is seen as an unnatural thing, perhaps a worldview consequence. I recently asked a zoo keeper if they had any crossbreedings between any of their animals. She said “Well, we don’t allow it on purpose. But it does happen sometimes. People don’t exactly broadcast it when they get a hybrid. It’s generally looked down upon and avoided, so we don’t know.” In the course of researching for this article I found another surprise. Hybrid Vigor is apparently a commonly observed consequence of crossing two species. Hybrids are in many ways, more physically fit, and often have longer lifespans than either of their parents. In an evolutionary model, the breaking off of two groups of organisms is necessary so that fixation can take place and the two groups can evolve independently of each other. What is good for one group would not necessarily be a good trait for another group. So I naturally expected that a hybrid would be a degenerate form of an earlier ancestor, (especially given sterility). I am still very much an evolutionist at heart.
On the contrary, mules, ligers, bengals, and mutts all have great physical characteristics which would be more in line with loss of genetic information during separation. When the disparate groups are rejoined again we get a little closer to the original creature that fathered them both. Unfortunately, this only goes so far as there have been numerous mutations entering into the genome since the first divergence. “Plant hybrids, especially, are often stronger than either parent variety, a phenomenon which when present is known as hybrid vigor (heterosis) or heterozygote advantage.” (Hybrids)
Degradation and Dispersion
One more key point: The answer to all fragile-animal-specific-environment questions is actually quite simple. As animals moved across the landscape they lost genetic information until they became very narrow. Once they reached a point of stasis they could continue to grow within their environment. Taking into account the effects of genetic entropy the animals that we observe today have accumulated 4,000 years of deleterious mutations after undergoing a major amount of genetic drift/fixation. Natural selection works best on lethal mutations, and if the selection cost for eliminating lethal mutations is high enough then it will tolerate a fairly high level of “inconvenient” dependencies that match the environment, dependencies that would be lethal in a different environment. An ideal example of this is the Koala, which is almost entirely nutritionally dependent on the eucalyptus tree in order to survive. In an area where there are no eucalyptus this dependency is lethal so it will only survive where the plant survives, Australia. Notice that the farther from the Eurasian continent we get, (dispersion) and the smaller the functional population is, (degradation) the more specialized/fragile species there are. If you doubt the feasibility of animals populating a new area we need only look to the recent recorded history of Hawaii which was little more than a barren volcanic rock before the settlers arrived. Also, the baramin model can explain why we find strange isolated species all over the world with tiny populations, like the Echidna. If the populations had been there for very long the inbreeding would have killed them off, as we are observing with the mass extinction of biodiversity that is still going on.
Transitional fossils are another piece of evidence that baraminology uses to establish continuity or discontinuity. The best example of this is horses in which we have a fairly diverse sampling of different types of the horse baramin, many of which are now extinct. The ability of our modern horse specimens to breed with each other is an affirmation of the fact they share a common ancestor so it is no surprise to find fossilized variations within the horse baramin. These can be called transitional forms between horse, donkey, zebra, etc. Perhaps a better word is intermediate form, because given genetic compatability the offspring is dependent on its parents DNA (that’s genetics), not based on the time at which it was conceived. Natural Selection then is not really progress but simply the extinction of species that can’t survive. Woolly mammoth couldn’t take the climate change, but most of its DNA is still preserved in elephants, so the baramin continues although depleted.
Further Comments: I see that all my picture hyperlinks are now broken. They pointed to a great listing of known hybrids, with a whole bunch of pictures. The site is gone now, that’s sad. I wonder why the site was taken down?