Life in the lab

Another way to determine what alternative life might look like is to try to invent it ourselves.

If we can create new molecules which can behave in life-like way, we may then go out and look for these in the environment, says Professor Steven Benner, of the University of Florida.

His team have created perhaps the closest yet to a man-made alternative form of life.

"We are announcing the first example of an artificial synthetic chemical system capable of Darwinian evolution," he told the conference.

"Is it alive? Well, I can tell you that it is not self-sustaining.

"You have to have a graduate student stand there and feed it from time to time, but it is evolving."

The molecule is essentially a modified version of our own DNA double helix - but with six "letters" in its genetic alphabet, instead of four.

These nucleotides pair up in strands, which can replicate, though only with the help of polymerase enzymes and heat.

"Sometimes mistakes are made in pairing and these mistakes are maintained in the next generation - it is evolving," said Prof Brenner.

"The next step is to apply natural selection to it, to see if it can evolve under selective pressure.

"The accepted definition of life is a molecule capable of Darwinian evolution, so we are trying to put together molecules that are capable of doing it."

But he questioned whether our definition of "living" is perhaps too "Earth-centric".

"Remember - just because you are a chemical system which is self-sustaining and capable of Darwinian evolution, that doesn't mean that is the universal definition of life," he said.

...fine...but what other definitions might we apply. According to my latest reading, life is defined not just as being capable of Darwinian evolution (i.e. hereditary descent with modifications), but is required to consume energy and...something else which I've forgotten right now (D'oh - will look it up and update this).

What caught my eye was the ability to create something life-like with a different DNA coding. Would be interesting to see if you could go the other way and reduce it to two letters - essentially a binary code!

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

p103-4.

But cases of great difficulty, which I will not here enumerate, sometimesoccur in deciding whether or not to rank one form as a variety of another, even when they are closely connected by intermediate links; nor will the commonly-assumed hybrid nature of the intermediate links always remove the difficulty. In very many cases, however, one form is ranked as a variety of another, not because the intermediate links have actually been found, but because analogy leads the observer to suppose either that they do now somewhere exist, or may formerly have existed; and here a wide door for the entry of doubt and conjecture is opened.

Darwin seems to have hit the nail on the head, here - this is where much creationist attack appears to stem from. They see all the evidence, but then say "but you're just guessing at the intermediate forms". Of course, we can nowadays compare DNA and the like, which (again) Darwin would have been most glad to have had. However, he goes on, in an effort to allay the problem raised by his last sentence:

Hence, in determining whether a form should be ranked as a species or a variety, the opinion of naturalists having sound judgement and wide experience seems the only guide to follow. We must, however, in many cases, decide y a majority of naturalists, for few well-marked and well-known varieties can be named which have not been ranked as species by at least some competent judges.

So...let's have a vote? Perhaps before the advent of being able to use DNA to place an organism on the tree of life by comparing its sequences to others already catalogued, this was indeed the best way. I suppose, in a way, the current strategy is also a majority vote - the majority of biologists agree that this method works as well as, or, in fact, better than, a rather subjective appraisal by a committee of naturalists.