But now we have new scientific evidence regarding horizontal gene transfer, a process where a piece of DNA is transfered from the genome on one species to another. This has been known to occur in single cell organisms for some time now.
The new evidence includes almost all types of species.
Scientists have known for many decades that prokaryotes such as bacteria and other microorganisms – which lack a protective nucleus enveloping their DNA – swap genetic material with each other all the time. Researchers have also documented countless cases of viruses shuttling their genes into the genomes of animals, including our own.
What has become increasingly clear in the past 10 years is that this liberal genetic exchange is definitely not limited to the DNA of the microscopic world. It likewise happens to genes that belong to animals, fungi and plants, collectively known as eukaryotes because they boast nuclei in their cells. The ancient communion between ferns and hornworts is the latest in a series of newly discovered examples of horizontal gene transfer: when DNA passes from one organism to another generally unrelated one, rather than moving ‘vertically’ from parent to child. In fact, horizontal gene transfer has happened between all kinds of living things throughout the history of life on the planet – not just between species, but also between different kingdoms of life. Bacterial genes end up in plants; fungal genes wind up in animals; snake and frog genes find their way into cows and bats. It seems that the genome of just about every modern species is something of a mosaic constructed with genes borrowed from many different forms of life.
... By the 1970s, however, other researchers had discovered ‘jumping genes’, or transposons, in much more than just corn, and the scientific community at large finally began to celebrate McClintock’s work, which earned her the Nobel Prize in 1983. Scientists now know that transposons are extremely abundant and often constitute large portions of a given genome: they make up more than 85 per cent of the maize genome and about half of our own. Some slice themselves out of one spot on a chromosome and move to another; others take a copy-and-paste approach, quickly multiplying. To make these jumps, transposons rely on two main strategies: either they include a genetic sequence encoding an enzyme known as transposase, which can chop a transposon out of its current location and reintroduce it elsewhere; or they use a different set of enzymes to produce strings of RNA that are translated into DNA and woven back into the host genome.
... At the University of Arizona, Margaret Kidwell was mating laboratory-raised females of the fruit-fly species Drosophila melanogaster with males caught from the wild. Kidwell was surprised to discover that the offspring of her matchmaking were sterile and rife with crippling genetic mutations.
Further experiments revealed that the source of these aberrations was a transposon later dubbed the P element, and that this mobile gene had infiltrated just about every wild population of D melanogaster sometime in the previous 50 years. By confining some groups of fruit flies to laboratories for so many decades, scientists had protected them from this infestation. Whereas wild flies had evolved strategies to repress the genetic chaos triggered by the P element, laboratory strains had not. So their hybrid offspring were vulnerable. Making things even stranger, researchers discovered that the P element originally jumped to wild D melanogaster populations from another fruit fly species, Drosophila willistoni.
Although the two fly species live in the same areas, they are sexually incompatible – so how did the P element make its extraordinary leap? One of Kidwell’s colleagues, Marilyn Houck, suspected that a mite known as Proctolaelaps regalis was the gene-smuggler. The mite regularly parasitises both D melanogaster and D willistoni, using its needling mouthparts to suck up nutrients from fruit fly eggs and larvae. Such a parasite could conceivably transfer DNA from the egg of one fruit fly species to another. Follow-up studies showed that mites feeding on fruit flies did indeed harbor the P element.
In the mid-2000s, Feschotte and his colleagues noticed some unusual patterns among the sequenced genomes of various mammals. Again and again, the lineage of certain DNA segments failed to align with established evolutionary relationships. They would find, for example, nearly identical sequences of DNA in mice and rats, but not in squirrels; and the same sequence would turn up in nocturnal primates known as bushbabies, but not in other primate species. It was highly unlikely that mice, rats and bushbabies had independently evolved the exact same chunk of DNA. Further complicating things, these puckish strings of DNA were not in the same position on the same chromosome in different species, as you would expect if they had been inherited the traditional way – rather, their locations were highly variable.
The reason, Feschotte and colleagues discovered in 2008, is that these DNA sequences were not vertically inherited genes; rather, they belonged to a widespread family of transposons, which the scientists dubbed SPACE INVADERS, or SPINs for short. SPINs have managed to insert themselves into the genomes of tenrecs, little brown bats, opossums, green anole lizards and African clawed frogs, in addition to bushbabies, mice and rats. In each of these species’ genomes, the transposons have multiplied either themselves or abbreviated forms of themselves thousands of times. And, in at least one case, mice and rats have adopted a SPIN transposon as one of their own, turning it into a functional gene that is actively read by the cellular machinery that translates genes into proteins, though its exact role remains a mystery. Over the past 30 million years, several SPINs have infiltrated the little brown bat’s genome and replicated an enormous number of times. This amplification coincides with one of the swiftest periods of speciation in the bat’s evolutionary history. It is by no mean’s conclusive proof that horizontal gene transfer encouraged the speciation, but it is indicative.
A different kind of transposon – one of the copy-and-paste variety – has spread through an equally diverse group of animals. In 2012, David Adelson, Ali Walsh at the University of Adelaide, and their colleagues, discovered that the transposon BovB – first found in cows (hence the bovine epithet) – is also present in anoles, opossums, platypuses, wallabies, horses, sea urchins, silkworms and zebrafish, to name a few. Once again, vertical inheritance via traditional evolutionary relationships could not explain the transposon’s haphazard materialisation here and there. On its epic journey through the tree of life, BovB has jumped between species at least nine times, and seems to have generally moved from reptiles to mammals.
Recently, while studying a virus that preys on wolbachia, Jason Metcalf and Seth Bordenstein of Vanderbilt University in Tennessee discovered the Napoleon of horizontal gene transfers: a little gene that has conquered every kingdom of life. The virus in question attacks and kills wolbachia using a gene named GH25-muramidase, which encodes an enzyme that can perforate bacterial cell walls. When Metcalf and Bordenstein traced the evolutionary lineage of GH25, they discovered a pattern of inheritance that looked anything but typical. The GH25 gene was scattered throughout the tree of life: in bacteria, plants, fungi and insects. This particular gene seems to have moved fluidly through the microbial world and then hopped laterally to viruses, plants, fungi and insects living in close association with different kinds of bacteria. ‘Every organism needs to fight bacteria off,’ Metcalf says. ‘If they can get a new method of antibacterial defence, that’s a huge evolutionary advantage for them.’
At this point, the tally is too high to ignore. Scientists can no longer write off gene-swapping among eukaryotes – and between prokaryotes and eukaryotes – as inconsequential. Clearly genes have all kinds of ways of journeying between the kingdoms of life: sometimes in large and sudden leaps; other times in incremental steps over millennia. Granted, many of these voyages are probably futile: a translocated gene finds itself to be utterly useless in its new home, or becomes such a nuisance to its genetic neighbours that it is evicted. Laterally transferred genes can be imps of chaos, gumming up or refashioning a genome in a way that is ultimately disastrous – perhaps even lethal to a species. In a surprising number of instances, however, wayfaring genes make a new life for themselves, becoming successful enough to change the way an organism behaves and steer its evolution.
The fact that horizontal gene transfer happens among eukaryotes does not require a complete overhaul of standard evolutionary theory, but it does compel us to make some important adjustments. ...
Now I have said before that if god/s were going to be involved in evolution to tweak species along certain lines that there were a number of processes available that could be the "vectors" of such activity. These include viruses injecting sequences into DNA, as well as transportation mechanisms like mosquitoes or tics etc that could act as needles to carry the viral bits to the desired species.
This is in fact what we see here, but there is a distinction that I want to make that is critical: the injections of SPINs into DNA is completely random, completely unguided, acting in fact no differently than random mutations, most often affecting non-germ cells, often lethal, rarely beneficial.
This random activity shows conclusively that there is no god/s directed injection of new DNA sequences into an existing species in order to (poof) make a new species. At best there is a wide open avenue of causation for novel genetic combinations that are random in nature, but which are open to natural selection when expressed and inherited, that the process was designed to allow changes to occur. At worst it shows no hand of god/s in the diversity of life.