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Pigs: The Missing Evolutionary Human Link

· Evolution,gene editing,3D bioprinting

For those of you who aren't familiar with the term, xenotransplantation is the transplantation of non-human cells, tissues, organs into humans. A lot of startups have recently entered the arena into developing human + pig hybrid animals, and utilising pigs to harvest human organs. Three Cambridge startups: Editas Medicine, Intellia Therapeutics and CRISPR Therapeutics are attempting to treat various diseases from cancer to blood disorders by developing a pig + human hybrid to grow human organs by gene editing. Scientists are following this UK lead in the United States at various universities, and this year have begun to inject human stem cells into pig embryos to produce human-pig embryos called chimeras.

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In the medical world, we are already familiar with using the parts of pigs for various medical conditions. For example, insulin is typically derived from pigs to be injected into humans, and estrogen from pigs are utilised for birth control pills. Many plastic surgeons also utilise dermal fillers made from pig fat and skin grafts for burn victims are derived from the epidermis of pigs. Now you may ask why pigs? Why not chimpanzees or apes or orangutans, our closest ancestors? However, recent research in the last ten years has discovered that pigs could be, in fact, one of our closest ancestors and that we share a remarkably similar DNA. In addition, researchers have discovered that when human genes are combined with pig genes, that they appear to fuse seamlessly together instead of cellular rejection of the foreign DNA as what happens with human and chimpanzee DNA and xenotransplants.

In 2013, a geneticist and PhD professor at the University of Georgia, Dr. Eugene M. McCarthy had theorised that humans are most likely a hybrid of chimpanzees and pigs. Geneticists have been developing hybrid, fertile offsprings in a variety of different plant and animal species for decades, including the Zebroid (zebra + horse), the Grolar Bear (grizzly bear + polar bear), Beefalo (domestic cattle + American bison) amongst others, the most well known being the Mule (male donkey + female horse), although the latter is known to be sterile.

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Professor McCarthy, in his argument, goes on to describe the various similarities between pigs and humans and the characteristics we share in common. Although his argument is that humans are the result of a hybrid between pigs and chimpanzees, recent developments in the understanding of the role of viruses could also account for these genetic similarities. As I mentioned in my last post on antibiotics, viruses are the known drivers of evolution, and through viruses, genetic information is inserted into the genome of the host using reverse transcriptase.

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Endogenous retroviruses (ERV) are genetic information that is not expressed, but which we share with a number of common ancestors. For example, whales and pigs have a grouping of the same ERVs as with humans, baboons, chimps and orangutangs. We can trace back the evolutionary precedents when we find the same ERVs in the genome from different species. Humans share many retroviruses with other species and have many traits that are not expressed; for example, we have genetic information for tails that we do not develop, although a minor number in the population do actually develop tails during fetal development before birth. This is not due to a mutation, but an error in the methylation process in which genes become expressed and turned on. The DNA methylation process during cell division usually prevents certain genetic information from becoming expressed, and turns them off so that although we all have the genetic code for tails and gills, we do not develop them.

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A small percentage of human babies develop tails due to a failure of the DNA methylation process to "turn off" genetic information that we possess but which aren't usually expressed.

The latest analysis also shows that human limbs share a genetic programme with the gills of cartilaginous fishes such as sharks and skates, according to research at Cambridge University. The "sonic hedgehog gene" discovered in the 1980s, is responsible for animals to form digits or fingers, although these genes are silent and unexpressed in fish. The gene for gills that we share with fish is responsible for the development of our voices and sense of hearing.

“The creatures outside looked from pig to man, and from man to pig, and from pig to man again; but already it was impossible to say which was which.” - George Orwell, Animal Farm

Mortiz the Clever Pig from Germany can play piano and work on many puzzle games.

Scientists have written that pigs possess high intelligence, emotional complexity, sense of time and other attributes that are beyond the scope of our companion animals, such as dogs and cats, and that we need to "rethink our relationship with pigs."

In history, many religions, such as Islam and Judaism have banned the killing of pigs and eating them. Could it be that our ancestors were more closely attuned to the similarities between humans and pigs? Many people have reported that the smell of bacon is strikingly similar to the smell of burning human flesh, and perhaps through atavistic instincts, we are either repulsed or attracted to the scent, depending on whether our ancestral lineages were cannibalistic or not. It is clear, however, that we can no longer deny that we share many of the same genes and attributes with pigs.

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There are however, larger ethical questions we must ask ourselves, as we begin to discover our close genetic relationship with pigs. Should we farm intelligent beings, such as pigs as a food source? Should we fuse human and pig embryos to grow human organs? Furthermore, what will happen to these pig-human chimeras once they are harvested for their organs? We have to remember as humans, we are still evolving, and that the actions we take now will determine the future of our progeny. Quite frankly, I reject the idea of utilising pigs for human organ harvestation and in our next punctuated equilibrium of evolution, I think the better method will be finding a way to regrow or regenerate our own organs via 3D bioprinting or in a fluid filled sac or pod via nanotechnology and incorporate CRISPR gene editing methods away from utilisation of the insulin, skin, estrogen, organs, fat, cells of an intelligent animal we are closely genetically related to further our mad scientist experiments.

Organovo (NASDAQ: ONVO) is a 3D bioprinting startup founded in 2007 in San Diego, California that develops human tissue and organs. Other startups in this sector include Rokit (founded 2012, South Korea),  Aspect Biosystems (founded 2013, British Columbia),  3D Bioprinting Solutions (founded 2013, Russia), and BioBots (founded 2014, Pennsylvania).

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Million years of evolution have taught us that many species often die out when they consume and kill their own kind. Although we have in ourselves, unexpressed predator genes, we also have developed high reasoning skills in the dorsolateral prefrontal cortex and an advanced limbic system in both sides of the thalamus of our brains that have evolved into empathy and compassion which we have inherited from our closest animal ancestors. It seems as we learn more about ourselves and where we came from, the key to evolution and survival has always been about love rather than seek and destroy.