Horizontal gene transfer: does influence evolution (Introduction)

by David Turell , Saturday, September 07, 2019, 18:35 (1683 days ago) @ David Turell

HGT does control the advances of evolution, and may have been active in very early life:

https://aeon.co/essays/genes-that-jump-species-does-this-shake-the-tree-of-life?utm_sou...

"Every creature that ever existed presumably ‘descended from some one primordial form’, as Charles Darwin put it in 1859. And genes ostensibly flow in one direction: up from the trunk.

"Scientists such as Ford Doolittle and Carl Woese at the University of Illinois have argued that this portrayal is an oversimplification. Rather than rising from a single trunk, they say, the tree of life stands on an interweaving root system. Rather than evolving from one ‘last universal ancestor’, all life arose from a communal pool of primitive cells with unbridled zeal for exchanging DNA. For relatively simple cells with only a handful of genes each, swapping DNA was an excellent strategy for acquiring and preserving the best adaptations around.

"At some point, Woese proposed, cells reached a certain threshold of complexity at which it became detrimental to embrace a bombardment of foreign genes. A primordial cell harbouring a small group of genes can potentially gain a lot by adding new genes to its repertoire; but a more sophisticated cell with hundreds or thousands of genes risks imbalancing an intricate genome fine-tuned by a longer period of natural selection. So, complex eukaryotic cells evolved new ways to protect their DNA and expunge genetic invaders.

"However, as has become clear in the past decade, horizontal gene transfer did not halt among eukaryotes and their microbial denizens. A mischievous breeze continued to blow DNA this way and that, from one branch on the tree of life to another. Wolbachia, pea aphids and hornworts all encourage us to accept a truth that seems unsettling at first, but ultimately invites us into greater communion with all life on the planet.

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"Genes are concerned with one thing above all else: self-perpetuation. If such preservation requires a particular gene to adapt to a genome it has never encountered before – if riding a parasite from one species to another turns out to be an extremely successful way of guaranteeing perpetuity – so be it. Species barriers might protect the integrity of a genome as a whole, but when an individual gene has a chance to advance itself by breaching those boundaries, it will not hesitate.

"That’s the thing about DNA: its true loyalty is to itself. We tend to think of any one species’s genome as belonging to that species. We have a strong sense of ownership over our genes in particular – an understanding that, even though our genome overlaps with that of other creatures, it is still singular, is still ‘the human genome’. So strong is our possessiveness that the mere idea of mixing our DNA with another creature’s – of any two species intermingling genes – immediately repulses us. As far as DNA is concerned, however, the supposed walls between species are not nearly so impermeable. Up in the branches of the great tree of life, we are no longer immersed in the ancient communal pool that watered its tangled roots. Yet we cannot escape the winds of promiscuity. Even today – as was true from the start – ‘our’ genes are not ours alone."

Comment: No question horizontal gene transfer is a major contributor to the course of evolution. The vast library of genes is standardized across life and all different organisms c an use them and modify their outputs. Woese, the discoverer of Archaea is a deeper thinker who may have a major point about early life. There is no top-down history of genes as Darwin and early Darwinists assumed.