Slideshow: Virgin Birth Not So Miraculous in Animal Kingdom

‘Tis the season for twinkling lights, wrapping paper, and virgin birth. For billions of Christians around the world, the holidays are a time to celebrate Jesus’s birth to the Virgin Mary. But for many animals, virgin birth is far from a miraculous event. Researchers have discovered a growing number of species that reproduce without assistance from the opposite sex.

Known formally as parthenogenesis, virgin birth occurs when an embryo develops from an unfertilized egg cell. The development of an embryo usually requires genetic material from sperm and egg, as well as a series of chemical changes sparked by fertilization. In some parthenogenetic species, egg cells don’t undergo meiosis, the typical halving of the cell’s chromosomes, before dividing into new cells. These offspring are generally all female and clones of their mother. Other forms of parthenogenesis occur when two egg cells fuse after meiosis.

Biologists think that sexual reproduction evolved as a way to mix the gene pool and reduce the impact of harmful mutations. Still, parthenogenesis can be beneficial if the mother is particularly well adapted to her environment, since all of her offspring will be just as well adapted.

Here’s a glimpse at some of the world’s most recently discovered parthenogenetic species:

Credit: National Prk Service

New Mexico whiptail (Aspidoscelis neomexicana)

Living in the deserts of the U.S. Southwest and parts of northern Mexico, the New Mexico whiptail is an all-female species of lizard. The creatures first arose as hybrids between two closely related species of sexually reproducing lizards: the little striped whiptail (A. inornata) and the tiger whiptail (A. tigris). Male hybrids aren’t viable, making this one of the few all-female species. Adult female New Mexico whiptails reproduce solely through parthenogenesis, laying unfertilized eggs that develop into other female whiptails.

Credit: Wikipedia

Komodo dragon (Varanus komodoensis)

In 2006, staff members at two zoos in the United Kingdom identified two female Komodo dragons that each laid an unusual clutch of eggs. The eggs developed into healthy offspring, even though neither female had been in recent contact with a male of that species. Genetic testing confirmed parthenogenesis. Although most Komodo dragons in the wild continue to reproduce sexually, this giant lizard is one of a growing number of vertebrates that reproduce parthenogenetically in captivity. Scientists still aren’t sure what triggers the switch.

Credit: Wikipedia

Freshwater water flea (Daphnia magna)

Found across North America and Eurasia, Daphnia species mostly reproduce by parthenogenesis. In the spring and summer, a female D. magna will let her all-female offspring partially mature in her abdominal brood pouch. After several molts, these females will produce their own offspring by parthenogenesis. The onset of winter, drought, or other environmental stress will trigger some of D. magna's developing parthenogenetic offspring to become males, who then mate with the parthenogenetic females. This method of sexual reproduction produces eggs with an extra shell layer that lets them survive the stressful period.

Credit: Wim van Egmond/Visuals Unlimited Inc.

Bdelloid rotifers (Bdelloidea species)

Like the New Mexico whiptail, bdelloid rotifers are all female and reproduce entirely by parthenogenesis. Despite tens of millions of years of celibacy, these rotifers are an amazingly diverse group with more than 300 species. The animalsappear to offset a loss of genetic diversity by eating any DNA floating in their environment and incorporating it into their genome.

Credit: Wikipedia

Marmorkrebs (marbled crayfish)

The parthenogenetic form of the North American crayfish Procambarus fallax, marmorkrebs are a popular aquarium pet. Their capacity for virgin birth was first discovered in Germany in 2003, when aquarium owners noticed that crayfish housed alone were laying eggs that developed into healthy adults. Genetic analysis and laboratory experiments confirmed that the animals were reproducing through parthenogenesis. Ecologists worry that their accidental release into the wild could seriously harm native crayfish, because a single individual can start a self-sustaining population, leading some states to prohibit their ownership.

Credit: iStockphoto/Thinkstock

Bonnethead shark (Sphyrna tiburo)

In 2001, a captive bonnethead shark (Sphyrna tiburo), a type of hammerhead shark (pictured), gave birth to a normal-appearing female offspring. When the pup died several days later, researchers discovered that the DNA of the pup was identical to its mother’s. Because the mother had not been around any males for the previous 3 years, researchers confirmed that the pup developed through parthenogenesis.

Credit: Tom Brakefield/Stockbyte

Boa constrictor (Boa constrictor)

Until 2010, boas were thought to only reproduce sexually. But when a female boa produced several all-female litters that carried a rare genetic mutation, scientists from North Carolina State University in Raleigh performed a DNA fingerprint analysis. Although the genetic studies indicated that the female offspring were the result of parthenogenesis, researchers have yet to untangle the cellular factors that explain how and why this happened.

Credit: Animals Animals/Superstock

Cape honey bee (Apis mellifera capensis)

This native South African bee reproduces through a specific type of parthenogenesis known as thelytoky, in which diploid females (which carry the normal double set of chromosomes) develop from unfertilized eggs. What’s unusual in these animals is that worker bees can produce offspring by parthenogenesis. Typically, the sexually reproducing queen bee produces all of the eggs in the hive.

How do you determine that those are new species and not simply new breeds? Is there an objective standard that can be applied, or is it just “fuzzy science”? If you define species so loosely as to have no objective standard, then saying a new one arises means next to nothing, objectively.

There is so much variation possible within biology that defining what is a "species" is a difficult process. Since many things do not have concrete definitions, scientists must take care to define terms as they use them--which means that one scientist's definition of "species" is not necessarily universal.

That said, the definition I use is that a species consists of a group of organisms that do not naturally breed outside of their group. This definition only applies to multicellular organisms that have dedicated organ systems. The definition of species in microorganisms is a bit more problematic.

I should mention that species which came into existence within the span of human history (within the last 10,000 years or so) include such familiar species as cows and corn. These did not exist before agriculture, and do not exist apart from human civilization.

Since humans and chimpanzees cannot interbreed, I would say probably not. The test of interbreeding is only conclusive for positive results, not negative ones, since there are breeds that are obviously of the same species (because we have bred them), yet they can no longer interbreed, which are basically false negatives.

For all I know, humans and chimps are completely capable of producing viable mixed offspring that may even be fertile. We choose not to. Many thousands of years ago, homo sapiens in what is now Europe interbred with homo neanderthalensis, yet the two kinds of humans are generally considered separate species. Chihuahuas and Great Danes do not interbreed, yet are generally considered the same species. It is not the fault of scientists that nature does not draw clear boundaries for us to use when trying to decide what separates different species, or that our language groups organisms in a manner that doesn't reflect nature.

“The theory as formulated by Darwin and refined by countless scientists since then is very much based in the laws of physics.”

I like how you didn’t say anything about biology and genetics. Sometimes what you don’t say is as important as what you do. Now, standard evolution doesn’t step on too many toes when it comes to Physics, but abiogenesis certainly does, and that theory is a natural consequence of the same assumptions that figure in to evolution.

I did not specifically mention biology and genetics, because all hard sciences are, in fact, different aspects of physics. Evolution very much proceeds according to the laws of physics. I'm not sure why you mentioned abiogenesis; I'm fairly certain it was definitively disproved back in the 1600s.

Objecting to a theory is not anti-science. Einstein objected to Quantum Mechanics, and he was not anti-science. In fact, the attitude that a theory should not be questioned is itself anti-scientific.

When the theory forms the basis of a whole group of scientific disciplines (in this case, the life sciences), then objecting to it is, in fact, engaging in anti-science. I do not consider blanket rejections of theory as being in any way comparable to the normal testing and refinement of theory that scientists constantly engage in. I seriously doubt that Einstein blanketly rejected quantum mechanics; most likely, he was not convinced by the evidence and thought there might be other explanations for the observations that led to the description of quantum mechanics.

“There is so much variation possible within biology that defining what is a “species” is a difficult process. Since many things do not have concrete definitions, scientists must take care to define terms as they use them—which means that one scientist’s definition of “species” is not necessarily universal.”

Yes, that’s correct, but I see that problem as a necessary consequence of Darwin. In Origin of the Species, one of his main contentions was not simply that species could vary, but that the very idea of species as truly distinct groups that were “quantized”, so to speak, was false. His theory depends on a notion of species that is highly gradated and flexible.

Conveniently, such a notion, once accepted by scientists, allows a lot of leeway to finding evidence for Darwin’s ideas. If his contention is wrong, then mistaken classifications arising from it can contribute to false evidence, claiming events as “speciation”, which would not qualify under a more accurate definition. Even if the contention is correct, the ethereal standards would make it hard for scientists not to introduce bias into their classifications, and hence into their evidence for speciation.

“That said, the definition I use is that a species consists of a group of organisms that do not naturally breed outside of their group.”

I’d say that’s a broad definition, because of the word “naturally”. Naturally could mean they don’t breed because of circumstances, such as geographic separation. Or it could mean that they don’t breed simply due to preference. Neither of those things gives us much useful biological information, so why should we base an important biological categorization on it? This is how we arrive at birds which are basically identical being placed in different species just because they live on different islands.

“I should mention that species which came into existence within the span of human history (within the last 10,000 years or so) include such familiar species as cows and corn.”

Again, citing these as speciation events, in defense of the theory, depends on a flexible definition of species derived from the theory. We invented agriculture, and bred existing wild bovines until we wound up with the varieties of modern cow, and likewise for maize. There’s no mystery as to how these varieties differentiated from their ancestors, it was simple breeding, not evolution.

“For all I know, humans and chimps are completely capable of producing viable mixed offspring that may even be fertile. We choose not to.”

Well, there was the legend of the Soviet scientist who may have tried it, but there’s probably no real data. Considering the vast morphological differences and the 2 extra chromosomes, I don’t think it’s a likely scenario.

“Many thousands of years ago, homo sapiens in what is now Europe interbred with homo neanderthalensis, yet the two kinds of humans are generally considered separate species.”

Yes, but under a different definition of species, this fact itself is enough to state that Sapiens and Neanderthals were not separate species. It’s a great example of how a flexible definition of species allows an evolutionist to support their arguments in a circular fashion.

If you call whatever you want a species, then you can classify two breeds as separate species, and if you find evidence those two breeds actually interbred, instead of invalidating your classification, it is cited as evidence that the flexible definition of species, which started the chain of logic, is correct!

“Chihuahuas and Great Danes do not interbreed, yet are generally considered the same species.”

Chihuahuas and Great Danes are only considered the same species because scientists are unable to deny the fact, since we have direct historical knowledge of their breeding, and so we know the origin of their morphological divergence. If, on the other hand, scientists only had fossils of Chihuahuas and Great Danes to work with, I have no doubt that they would be classified as separate species.

“It is not the fault of scientists that nature does not draw clear boundaries for us to use when trying to decide what separates different species, or that our language groups organisms in a manner that doesn’t reflect nature.”

Well, as to the first part, it may be difficult for us to determine clear boundaries sometimes, but I don’t think that means they do not exist. We can determine some boundaries with certainty, and others we cannot. Darwin took that as evidence that the boundaries should be questioned, while I take that as evidence that our methods are simply less than optimal.

“I did not specifically mention biology and genetics, because all hard sciences are, in fact, different aspects of physics. Evolution very much proceeds according to the laws of physics.”

Above of the quantum level, physics is fairly deterministic. We observe a phenomenon, and if our theory is correct, we can use the theory to predict the phenomenon accurately. Now, evolution depends on random factors to contribute changes to a genome. Absent these factors, the genome is recombinated and selected, but it’s not producing a new species. So, the basically deterministic processes of reproduction and selection contribute to shifting existing genetic information within a species, but the random processes must contribute the necessary new information.

That’s why evolution requires timescales on the billions of years, because, without them, the proposal that the regular deterministic processes, normally dominant in our scale, would be essentially dominated by the irregular random processes, is not sensible. It’s like suggesting that the random molecular motion of the water molecules in the ocean could overwhelm the gravitational influence of the moon, from time to time, if everything aligned correctly. It could happen, but if you base a theory on the necessity of it happening, with regularity and to a degree that has a statistically significant result, you need a timescale that starts heading towards infinity.

That aspect of the theory isn’t deterministic, and it just creates a nebulous notion of causality that can be stretched to accommodate any bias. To make matters worse, we apply that notion in retrospect, to events we can’t really witness, and let our speculations run amok. There’s no need to propose a testable hypothesis as to how the nondeterministic forces caused a specific change that the deterministic forces could not, it’s just taken as a given. They become the “deus ex machina” to answer any question on demand. That is not in line with good physics, as far as I’m concerned.

“I’m not sure why you mentioned abiogenesis; I’m fairly certain it was definitively disproved back in the 1600s.”

I think you are thinking of spontaneous generation, which was just a certain flavor of abiogenesis. Currently, abiogenesis usually refers to the idea that life originally arose from non-living matter of some sort. It’s a general assumption of a broader kind of evolutionary thinking, that includes areas like the current cosmological model, stellar evolution, planetary formation, etc. It’s not a part of the stricter definition of just the biological theory, but since the biological theory is generally accepted, and since science is naturalistic, it is almost a natural consequence to assume abiogenesis.

“When the theory forms the basis of a whole group of scientific disciplines (in this case, the life sciences), then objecting to it is, in fact, engaging in anti-science.”

Nonsense. It doesn’t matter how much science has been built up around a theory, it’s never “anti-science” to raise challenges to it. That is simply defending orthodoxy for orthodoxy’s sake.

“I do not consider blanket rejections of theory as being in any way comparable to the normal testing and refinement of theory that scientists constantly engage in.”

First of all, few people blanketly reject evolution. I don’t argue that natural selection is incorrect, and that is a fundamental part of the theory. If I were to support another model, it would have to incorporate natural selection, so it would necessarily be a refinement of the existing theory. Refinement doesn’t exclude the abandonment of even a major part of a theory.

“I seriously doubt that Einstein blanketly rejected quantum mechanics; most likely, he was not convinced by the evidence and thought there might be other explanations for the observations that led to the description of quantum mechanics.”

He didn’t blanketly reject QM, and I don’t blanketly reject evolution either, so where is the “anti-science”? I think it’s a flawed theory which leads to flawed results, and I have plenty of arguments to support that. I may prove to be wrong in my arguments, as Einstein proved to be after Neil Bohr and company bested him, but I’m not “anti-science” for making them.

First of all, as a working scientist, I have never read and will probably never read On the Origin of Species. I spend all day long reading about the latest advancements in my current field; I simply do not have the time or energy to read a historical document. When I speak of evolution, I speak of the current theory or of the biological process, not of Darwin's particular formulation of the theory, which has undergone considerable refinement.

The problem of trying to define species is that nature did not produce distinct groups of organisms that could be neatly categorized into different species. That isn't a problem of definition, it's the essence of biology.

Speciation is not an event, but a continuously on-going process. Think of how a baby becomes an adult: it is not the result of an event, but of slow change occurring over several years. There are no distinct lines between infant and toddler, toddler and child, child and adolescent, etc. Clearly, humans and finger monkeys are separate species, but if one could go far enough back in time, observing specimens every few generations, one would see the two species eventually converge until they appear to be the same.

I should also add that no one is trying to "find evidence for Darwin's ideas." Darwin used the experience of decades of personal observation, as well as the body of scientific literature from his time, to develop his theory. The theory in its modern form provides a guide for further research. The evolutionary process is a central feature of biology that cannot be ignored when trying to do research.

I purposefully used the word "naturally", because humans can intervene and force all kinds of breeding or hybridization that does not occur spontaneously. If you take into account cross-breeding forced by humans, then the already blurry idea of species becomes even more muddy. Factors such as geographic location or breeding preferences are quite important. When a population is split, the longer the two parts of the original population are separated, the more different they become. At some point, they become different enough to warrant being called different species.

Were it not for the evolutionary forces shaping biology, no amount of breeding would have produced cows or corn. In scientific terms, natural selection describes the process by which populations change, becoming gradually more suited to their environment, and artificial selection where humans breed only those individuals with traits that benefit the humans. These are both evolutionary processes.

I've heard rumors of Soviet human/chimp breeding experiments, but I have no evidence that such unethical experiments ever happened. The fact that two ape chromosomes fused at some point to become one human chromosome isn't such a big deal, really. The genes are all there in either case, and our genomes are nearly identical. I can think of no biological reason that a human/chimp hybrid could not exist; what keeps us from making that hybrid is our sense of morality.

Anyway, I will have to finish this later. I must head off to work, where no doubt, I'll be spending several hours reading about the consequences of evolutionary pressures. In the area of public health, evolution is a rather big consideration.

“I simply do not have the time or energy to read a historical document.”

That’s a shame, because it gives great insight into the nature of the theory. It wasn’t until I read Origin that I began to realize just how circular the reasoning was by which Darwin supported his assertions. The theory has been refined, but it is still dependent on most of those assertions, so it’s good to examine his reasoning if you want to critically examine modern evolutionary theory.

“The problem of trying to define species is that nature did not produce distinct groups of organisms that could be neatly categorized into different species. That isn’t a problem of definition, it’s the essence of biology.”

This is essentially just repeating a tenet of evolution as fact. It’s an assumption that’s absolutely essential to evolution, so I’m not surprised that it’s usually taken as a given.

Ask yourself, though, how is that scientifically established? What experiment demonstrates that there are not distinct groups of organisms? Darwin inferred this from observation, but didn’t establish it himself, and even admitted in Origin that, if it were found not to be true, it would be very damaging to his theory.

“Speciation is not an event, but a continuously on-going process.”

Yes, of course, that’s a crucial point of the theory. However, by “speciation event” I’m talking in the context of a rapid or significant instance of the process that can be cited as dramatic evidence for the theory. If you are going to cite something as insignificant as a wild bovine becoming a domestic bovine as evidence for evolution, then you’re not providing any evidence for the more radical assertions of the theory, just the parts that everyone agrees on.

“Clearly, humans and finger monkeys are separate species, but if one could go far enough back in time, observing specimens every few generations, one would see the two species eventually converge until they appear to be the same.”

That’s a nice story, but we cannot go back in time, and nobody ever has seen such a thing, so it’s really just a fantasy. Finding a chain of skeletal remains that you can arrange in order of similarity, from monkey-like to man-like, does not establish that such a progression actually occurred as evolution predicts. Similarly, arranging genomes by similarity doesn’t establish that the similarity is due to common ancestry.

“I should also add that no one is trying to “find evidence for Darwin’s ideas.””

Well, in practice, his ideas are simply assumed to be correct, and any evidence that is found is interpreted as if those ideas were correct. So, any new or existing evidence is never critically examined to determine whether it might contraindicate the theory, but instead it is interpreted in the manner which best supports the theory. So, the result is that scientists are fitting the evidence to the theory, even if they are not consciously trying to do so. It’s simply the result of their assuming the theory to be true and hardly ever bothering to consider possible alternatives to it.

“If you take into account cross-breeding forced by humans, then the already blurry idea of species becomes even more muddy.”

Which I would cite as evidence that the idea is faulty, and should be refined in light of our experience.

“When a population is split, the longer the two parts of the original population are separated, the more different they become. At some point, they become different enough to warrant being called different species.”

At what point? This is another of the flaws of the theory. The groupings must be indistinct enough to allow for the idea of macroevolution to be tenable, yet, we observe distinct groups in nature that must be accounted for. So, there is this nebulous, undefined event where an organism undergoing gradual changes suddenly is not able to breed with its closely related organisms. Breeding is not a gradual event, it is a fairly yes/no affair, so the species cannot gradually lose the ability to interbreed.

At some point, they can interbreed, and then, they cannot. This is a “speciation event”, that really hasn’t been documented or explained by scientists. The mechanics of such an event, for sexually reproducing organisms at least, are a logistical nightmare. If a mutation causes the final change, then the first offspring of the new species is not sexually compatible with at least some of the members of the parents species. Since we don’t know exactly how the incompatibilities work, we can’t be sure that the offspring would be compatible with ANY of the parent species. If that were the case, it would simply be a dead end, an effectively sterile mutant.

Even partial sexual incompatibility is a fundamental disadvantage that isn’t taken into account in the evolutionary calculus. A beneficial adaptation that resulted in this kind of speciation would have to be advantageous enough to overcome a fundamental handicap to the essential process of the organism’s survival. Yet, that hurdle never seems to be addressed. Scientists simply pretend it isn’t there.

“These are both evolutionary processes.”

I feel like we’re talking in circles. Have you ever discussed evolution with a critic before? Nobody disputes natural selection, artificial selection, or changes resulting from recombination, or even parasitizing genes from other organisms. When critics speak of something not being evidence of evolution, we’re not speaking of them not being evidence of those processes. We are speaking of them not being evidence for what is sometimes called “macroevolution”, the part of the theory that says all organisms share common ancestry, and all species, no matter how distinct, have arisen from the gradual changes produced by the processes.

So, a wild animal changing as it is domesticated, by well understood and accepted processes, isn’t evidence for macroevolution, which is what is in dispute. Many domesticated animals and plants can still revert back to forms similar or identical to their wild progenitors, demonstrating the relatively minor variations we are introducing by these processes. The variations we introduce can seem dramatic, because we can essentially accelerate the selection process, but we’re not similarly accelerating the proposed processes necessary for macroevolution, such as mutation, so we will never see, say, a cat bred into a non-cat. It simply can’t happen by those processes.

“The fact that two ape chromosomes fused at some point to become one human chromosome isn’t such a big deal, really. The genes are all there in either case, and our genomes are nearly identical.”

We have no real definite knowledge of how much difference in the genome can exist and still allow interbreeding, so the only real test is to try it. We have many similarities in our genomes to gorillas as well as chimps, yet they can’t interbreed with each other, and I doubt either could interbreed with us. Until someone tries it, I guess it will be an open question though. I wouldn’t hold out much hope for a humanzee though :)

Okay, let's just stop right here. When you have to copy/paste or paraphrase the same old anti-science nonsense that's already infesting the web in multitudes of anti-science "creationist" sites, that tells me that you have *no* education in science or the scientific method. It also sends me the message that you have no desire to learn any real science. Claiming that you've read On the Origin of Species and "realized" just how circular Darwin's reasoning was--a meme that is widely propagated on anti-science "creationist" websites--does nothing to convince me that you know *anything* about the theory, either as it was originally proposed by Darwin, or in its current form. If you are going to assert supposedly circular reasoning, can you explain how/why the reasoning is allegedly circular? Hint: science is a cyclical/iterative process; to someone who is clueless, I suppose cyclical could appear circular. But it's not.

Here is an example of circular reasoning:

The Bible is infallible.
Why is it infallible?
Because it is the word of God.
How do you know it is the word of God?
Because it says so in the Bible, and the Bible is infallible.

Notice how there is NO exterior corroboration of any of the assertions.

I will say one more thing about theory. Theory is an explanation of a physical process that is formulated (and refined) on the basis of extensive observation and testing. The physical process--in this case, evolution--does not change because someone made a theory to describe it. Gravity doesn't exist because of gravitational theory. The electromagnetic spectrum doesn't exist because someone formulated the theory of electromagnetism. And evolution did not spring into existence just because Darwin proposed an explanation for it.

Bonus question: what were some of the other theories of evolution, and how did they fail to withstand experimental testing? (For a double bonus, answer that based on real science, and not on what you read at Answers in Genesis.)

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