The dominant thinking in evolution focuses on inheritance between parent and offspring - or ‘vertical gene transfer (VGT)’. But now scientists are paying more attention to ‘horizontal gene transfer (HGT)’: the transmission of DNA other than from parent to offspring, as this transfer can tell us about the evolution of a number of other organisms such as bacteria. It can also help us to better understand antibiotic resistance.
I’m still trying to understand the basics of evolution. This article came up in my news feed. What are the “rules” that this instance bends them?
The title of the article is sensationalistic. This “bends the rules of evolution” only if evolution is perceived as Darwin described it 150 years ago. Darwin envisioned a slow process that occurred only as parents gave rise to offspring. Horizontal gene transfer involves the input of new genetic material from neighbors, not just parents.
The importance of horizontal gene transfer in evolution has been recognized for decades. Although the effects and mechanisms of HGT are best known in prokaryotes, it is also important (in the big picture) for eukaryotic evolution. I’ll hop over to the computer to share a thread in a bit.
It doesn’t actually drive any evolution when evolution means evolution from microbes to humans (microbes to humans evolution was the main conclusion of Darwin’s theory, all life in earth can be derived from a common ancestor). This is because in this process only existing information is transferred, so it does not produce the new genetic material that would be necessary for the evolution from microbes to man.
I do not recommend using the word evolution if it is intended to refer only to change. Because the word evolution is commonly understood (especially in the context of Darwin’s theory) as a kind of change, that is, one that would lead from microbes to human evolution. Kerkut, for example, tells us that evolution is “the theory that all the living forms in the world have arisen from a single source which itself came from an inorganic form.” Kerkut, G.A. (1927–2004), Implications of Evolution, Pergamon, Oxford, UK, p. 157, 1960
That’s a bit too simplistic. While humans did evolve from prokaryotes, many other organisms did too(plants, animals, fungi, and innumerable other strange multicellular organisms), while the vast majority of other prokaryotes remained as prokaryotes
Evolution is a process of diversification, not necessarily continuos increases in complexity or whatever other measure you might find interesting.
The significance statement alone seems to describe the situation pretty well:
Bacteria can obtain genes from other bacteria, or the surrounding environment, by horizontal gene transfer (HGT). While it is clear that HGT is very important for microbial populations, it is not understood how HGT changes the rate or mechanisms of adaptation. In this study, we evolve populations of the bacteria Helicobacter pylori and use DNA sequencing to track the movement of HGT genes as they spread through the population. We show that HGT can help antibiotic resistance genes establish at a low frequency in a population, even in the absence of the antibiotic. We find that these HGT treatment populations flourish when treated with antibiotics, showing how HGT can potentiate adaptation to future environmental change.
This means that a potentially novel adaptive trait(such as resistance to an antibiotic) can spread through a population quickly, facilitated by horizontal gene transfer, even before it becomes beneficial when the environment changes(before the bacteria even encounter the antibiotic).
So basically a mutation can result in antibiotic resistance, and the DNA encoding this resistance mutation can be released into the surrounding environment, where other bacteria can pick it up and copy it and use it themselves.
In this way a large number of bacteria can essentially evolve antibiotic resistance just by chance, before even encountering the antibiotic, so when and if their environment changes to contain the antibiotic, they’re already adapted to it.
Such changes can be predicted from the Bible. In other words, based on biblical revelation, we can predict that God gave organisms the ability to adapt to different conditions in the world and it follows that we expect to see change in allele frequencies in populations. So if you want to use such a definition of evolution, then remember that it is in no way against the revelation of the Bible and the YEC model. Secondly, it also says nothing then about the evolution that Kerkut defined it.
Bacterial antibiotic resistance indicates that evolution is going in the wrong direction from the point of view of evolutionary theory. Bacterial resistance to antibiotics is based on disruption of an already existing function and therefore cannot be used as a basis for evolution from microbes to humans, which would be the most important point of view for evolutionary theory.
Thus, antibiotic resistance in a bacterium is a loss caused by a mutation that, under certain (antibiotic-containing) conditions, provides the bacterium with survival and selection advantage. Nothing new (new alleles) has evolved. Resistant properties were in resistant forms even before the selection and adaptation event. Only the pre-existing property was lost and therefore the bacterium benefited under exceptional conditions (containing antibiotics). The bacterial population is now specialized - i.e., the next population specializes only in resistant forms of the original population - with other forms being selected out.
That is, the next bacterial population as a result of selection lacks all those bacteria whose enzyme had not been disrupted by the mutation. Thus, the gene pool of the next bacterial population contains only a portion of the allelic set of the original total gene pool. The gene pool is poorer than the original gene pool. Such a loss of information is the opposite of what the theory of evolution would need to function, and it does not create any new property or structure that evolution from microbes to man would require in order to function.
Yes, natural selection is not a prerequisite for the horizontal transfer of genes. Though those genes are of course still subject to natural selection once transferred. If the transferred gene is of no use to the receiving organism, it will eventually be lost again.
Not really. I don’t think the speed of change is a surprise.
No, there’s a process by which bacteria can copy DNA and pass it around(in the form of plasmids), either by releasing it into the environment where other bacteria can ingest it, or by a specific process known as bacterial conjugation where bacteria basically sit next to each other and directly transfer DNA from one to the other.
@thoughtful the Science Direct report mentioned the speed factor, if I’m recalling correctly. The genetic changes that took place didn’t take place at a surprising rate, but the HGT prior to exposure to antibiotics helps explain how the phenotype - in this case, the development of antibiotic resistance - can change rapidly as a result of previous change in the bacterial DNA content.
No. Evolution makes no claims about what “direction” antibiotic resistance should be gained. There is no aspect of the theory of evolution that says what the nature of antibiotic resistance mutations should be.
That is one way by which that can evolve. It can also evolve by de novo gene birth, that is the evolution of a novel protein coding gene that has a function that gives antibiotic resistance.
In this paper scientists give bacteria plasmids encoding randomly generated genes(stretches of DNA encoding random sequences of amino acids), and find that there are genes among them that give antibiotic resistance by having a novel function. One of these genes, when expressed, results in a peptide that functions as a membrane channel that depolarizes the bacterial membrane, leading to a large reduction in antibiotic uptake, and therefore a significant increase in resistance.
‘Evolution’ is a technical term used by scientists. If you want to talk to scientists about their field of study, it’s a good idea to learn their vocabulary (or ask them to translate it for you), rather than trying to get them to change it to suit your tastes.