The Smallest Genome and Irreducible Complexity
The latest issue of World Science has an interesting article related to the search for the origins of life. It's entitled "Tiny genome may be melting away, study suggests" and discusses the discovery of the very small -- miniscule by expected comparisons, really -- bacterium known as carsonella ruddii. Now, carsonella ruddii is a bacterium that lives inside an Arizona insect, Pachypsylla venusta, a.k.a. the Hackberry Petiole Gall Psyllid (pictured at right), which lives on tree sap.
Okay, what surprises the scientist is that little carsonella ruddii is much, much smaller than the expected 400,000 letters of genetic code necessary for life. In fact, it is less than half of that size. According to the article, it has "182 functional genes. These correspond to 160,000 'letters' of genetic code; previous estimates had placed the minimal genome at about 400,000." Wow! Even the scientists are amazed:
"It’s unbelievable, really," said Nancy A. Moran of the University of Arizona in Tucson, Ariz., one of the scientists who conducted the new research. "It’s believed that more genes are required for a cell to work." The finding provides new insights into bacterial evolution, Moran and colleagues wrote, also in the Oct. 13 Science.
Does this mean the end of Intelligent Design's claims for evidence of a designer of unknown origin based on the problem of irreducable complexity? Not really. It's important to really look at what's happening with little carsonella ruddii. First and foremost we're still talking about 160,000 letters in 182 functional genes. Since the research is seeking the absolute simplest cell, it is not as if the 182 functional genes representing 160,000 letters evolved. That's not possible since evolution occurs only amongst living things. Thus, we are still in a state where this 182 functional genes had to come together by chance -- a highly unlikely scenario as anyone who has ever played the lottery can tell you.
Moreover, it's important to remember that the collection of genes doesn't function as an organism unless they're in a particular order -- much like the words in a book wouldn't make much sense if they were randomly written. Thus, in addition to 182 functional genes coming together, they had to come together in the correct order to be able to work as a functioning, living organism. To get an idea of how improbable this is, think about how many ways 10 things can be ordered. Just getting ten things together by chance is tough enough, but any ten items can be put together 10! (10 + 9 + 8 + 7 + . . .1 = 55) ways. In other words, if there are 10 things that need to come together in only one way, assuming that the 10 things can be brought together naturalistically by chance, there is only a 1 in 55 chance that they will come together in the right way.
Now, consider if there are 182 things (like functioning genes) that need to be put together in a particular order. That is 182! or 182 + 181 + 180 + . . . + 1 possible combinations with (as far as we know) only one being workable assumuing that all 182 genes will come together in one place sheerly by chance. The odds that they would arrange themselves in the correct order by chance are 16,653 to 1 against which is, to put it mildly, quite extraordinary.
Second, little carsonella ruddii isn't making it on its own. Like a man strapped to life support, carsonella ruddii wouldn't be able to survive independent of the life-sustaining help of its host. You see, carsonella ruddii is a parasite that not only has to be with its host to survive, it appears to be actually morphing to become a mere biological organelle of the host. Consider the following from the World Science article:
Like a cash-strapped company that has to merge with a richer firm to keep going, they say, the microbe and its genes seem to be literally fusing into a larger creature, becoming cogs in its cellular machinery.
To live, such insects often rely on resident bacteria that make and share key nutrients with them. The host and microbes depend on each other to live, a relationship called endosymbiosis. The bond is so close and ancient that the microbes live within special insect cells that have evolved to house them, called bacteriocytes.
The bacteria thus live in a sheltered world with a simple, predictable diet and lifestyle. So they get by with simple genetic instructions. If they or their ancestors had any extra, unneeded genes, these would generally have been lost over the course of evolution.
The researchers collected Pachypsylla venusta bugs from hackberry trees on their university campus and around town. They extracted the Carsonella DNA and sequenced it, and got a jolt. "It lost genes that are considered absolutely necessary. Trying to explain it will probably help reveal how cells can work," said Moran.
The scientists speculate that in the bacterium’s evolutionary past, some of its genes moved into the insect’s own genome, beginning a process of gene takeover.
Animal and plant cells have specialized internal structures called organelles, tiny sacs of machinery used for various purposes. Strong evidence suggests many of these organelles are descendants of symbiotic bacteria that once lived free, but gradually became incorporated into the cell. A transfer of genes from the bacterium to the host is often part of the process.
Carsonella may likewise be turning into an organelle, the researchers wrote.
In other words, little carsonella ruddii not only cannot survive on its own without the host, it's actually giving up the ship and fast becoming an organelle in its Psyllid host. So, in other words, while it is a living organism with only 166,000 letters of genetic code, that is not enough to allow it to continue in existence on its own. It can only survive by freeloading on the more complex Psyllid organism, and such dependence is so complete that it is actually merging with the Psyllid as a means of continuing survival.
So, while this is truly interesting, it seems to me that it supports the idea of irreducible complexity because the study seems to suggest that while an organism may need fewer that 400,000 letters of genetic code to be able to "live", such life can only exist if it has a more complex organism already in existence which it can use to serve the functions that it cannot itself serve with its fewer functioning genes. In fact, in this case the researchers believe that little carsonella ruddii had to, at one time in the past, been more complex but lost them over time due to its symbiotic relationship with the Psyllid host.
Thus, while there may be some form of life that is possible to live for a short time, it seems to me that this research does little to support the idea that an organism could function, long term, on significantly less than 400,000 letters of genetic code. Certainly, it doesn't appear that the earliest life couldn't have been significantly less than 400,000 letters and survived without some other entity already in existence that had at least that number.