Horizontal Gene Transfer

A recent article in New Scientist talks about how Horizontal Gene Transfer (HGT) may well be a turning point in the Darwinian view of how life has evolved. It is pointing out that, from recent research, much of the genetic material in the eukaryotic and archaean organisms is transferred, not 'vertically' - by sexual reproduction - but 'horizontally', by swapping genetic material or by hybridisation.

It further suggests that this also happens in the prokaryotic branch of the tree - that which includes the majority of multicellular organisms, including ourselves. It points out that methods of horizontal gene transfer might occur through mediating viruses which cut and paste genetic material between hosts. It can also occur via hybridisation, where two separate species cross. This, according to Loren Riesberg, is the case for about 14% of plant species. There is also some evidence that this may have happened in early humans, between our ancestors and concurrent species, such as Homo erecutus and Neanderthals.

Personally I feel that some of this is a bit fuzzy. Firstly, the article suggests that DNA is subject to vertical transfer, but HGT can be seen in RNA. While perhaps that is just poor wording in the article, it feels from the first that the article is trying a bit too hard to make a point - and starts out almost hostile to the tree-of-life view, and so I wonder if it's trying to hide something there in order to prove a point. The article does ease up towards the end, describing the different viewpoints of scientists who feel that the tree of life needs to be 'uprooted' and those who feel that HGT just adds a new dimension to the data.

As far as the hybridisation comments, it would seem odd that where speciating groups overlapped they did not hybridise to some extent if they were able to. In fact, I am fairly sure this is what Darwin talked about in Ch. 4 or 5.

In the article it asks whether the tree-of-life view does not still apply to multicellular organisms. And replies - almost, at least - "Well, they aren't the majority, so we shouldn't bother with that view anymore". If the tree is still the way in which some genetic material is transferred, then, whatever other methods are available for its transfer, it is still a valid view.

I kept thinking "Newton...Einstein" throughout reading this, and, sure enough, right at the end he says:

If he [Michael Rose] is right, the tree concept could become biology's equivalent of Newtonian mechanics: revolutionary and hugely successful in its time, but ultimately too simplistic to deal with the messy real world.

Some of the things mentioned in the article gel with my feelings about early life - knowing that single-celled organisms can only reproduce by copying made me wonder about how genetic variety worked before sexual reproduction occurred.

I guess we live in interesting times - and I am sure the Discovery Institute is going to have a field day with this. It will be interesting to watch how it all develops.

On reading The Origin of Species

p. 110

Where many species of a genus have been formed through variation, circumstances have been favourable for variation; and hence we might expect that the circumstances would generally be still favourable to variation. On the other hand, if we look at each species as a special act of creation, there is no apparent reason why more varieties should occur in a group haveing many species, than in one having few.

In other words, and turning the statement on its head somewhat, where the environment (and/or other factors) have allowed an organism to diversify and we find many different varieties, we are more likely to find a greater variety of allied species of the organism than in the opposite case where the environmental factors have not been favourable to the diversification.

Darwin goes on to make the case for this statement with real-world examples.

On reading The Origin of Species

It looks like Darwin was driving at exactly the idea I had had - presumably because I am actually understanding what he's saying!

From these remarks it will be seen tht I look at the term species, as one arbitrarily given for the sake of convenience to a set of individuals closely resembling each other, and that it does not essentially differ from the term variety, which is given to less distinct and more fluctuating forms. The term variety, again, in comparison with mere individual differences, is also applied arbitrarily, and for mere convenience sake.

I still have to look up what the advantages of continuing to use this dichotomy (or, as Darwin points out, trichotomy - individual difference, variety, species) is. Convenience is an obvious candidate, as is custom - "we've always done it like this"

On the definition of "species"

Apparently there are some 18(? must check) definitions for 'species'. The creationist's arguments imply that 'evolutionists' only use one of the definitions - or use the one that suits them at the time...

In the former case, it would be interesting to note any examples of speciation for each particular definition.

In the latter case, well, much the same - but if a speciation event by each of the different definitions can be shown, is that not sufficient to prove that speciation does occur via natural selection?

Things to look up:
1) How many definitions of 'species' or 'speciation' are there (How many does evolution claim? How many do creationists claim?)
2) Examples of speciation under each definition.