ADRIAAN

Some almost random thoughts..

Wednesday, October 8, 2008

Life and the Evolution of Sex

Life is a replicating molecule. This replication is imperfect and sometimes errors in the copying of the replicator occur. The evolution of life is best understood as the replicator 'sliding down the hill of replication errors'.

See the diagram below, each red dot is a replicator that is still alive today. Every mutation that manages to crowd out the original or split off makes the replicator drop downhill. Uphill we find the least-mutated life forms still alive today. Towards the bottom of the hill we find the most-mutated forms still alive today. All life forms originate from the top, from the same replicating source, and have been alive for the same amount of time.

Nothing that happens downhill can serve as an explanation for anything uphill, because faulty replication is not a process that can look ahead in any way. Downhill, replication generally becomes more energy intensive and the replicator becomes more vulnerable to external disturbances due to the specialisation on specific energy sources. This vulnerability causes most life forms to die out as they slip further downhill.

Image

Sexual reproduction.
A mutation to a replicator stumbles upon sexual reproduction. Now mutations that survive without fixating are allowed to build up among the sexually reproducing organisms. Sexual reproduction changes the single gene line into a gene pool of genetic diversity available to the replicator.

The introduction of a gene pool causes two important changes to life:

1. A replicator building its organisms from a gene pool gets an extra lease of life because it gains a resistance against external disturbances. It can adapt within the gene pool without further mutations (like the peppered moth being able to adapt to the colour of the trees) keeping the replicator alive for longer. The genetic diversity within the genepool acts as a buffer against external disturbances allowing the replicator code to stay alive through genetic recombination.

2. The sexually reproducing replicator becomes more vulnerable to mutations, causing increased complexity and speciation. A mutated gene can recombine in many more ways than before. This increases the chance of finding a combination that is capable of crowding out the original or splitting off, causing it to drop down the hill.

But these two effects can not be the cause of sex appearing in evolution. They occur downhill from where sexual reproduction first occurs, after the build-up of a gene pool by further mutations.

The cause of sexual reproduction is the increased energy efficiency offered by building in an error prevention and correction mechanism in the replication process, allowing the mutated replicator code to crowd out its original. Sexual reproduction prevents the replicator from wasting energy on building faulty organisms that won't make it to replication (see earlier posts). This lets the sexually replicating version achieve a higher growth rate on the available resources, crowding out the original.


Cause and effect of sexual reproduction.
This clear distinction between horizontal 'adaptation within the genepool' and vertical 'mutation downhill' can explain the cause and effects of sexual reproduction. The abundance of sexually reproducing life in today's world is due to the buffer a genepool provides against external disturbances and the increased vulnerability of the replicator to mutations that can take over or split off. Sexually reproducing life is caused by a mutation introducing an error check in replication which allowed it to crowd out the original.

Present theories on evolution lead to confusion because they clump together adaptation within the genepool and mutation 'downhill' into a general mechanism called adaptation/evolution. To understand the cause and effect of sexual reproduction, these two aspects of life need to be clearly separated, like the model of the 'hill of replication errors' does.

Adaptation happens only within the genepool (by my definition). It is a largely reversible, almost directed process. Life is bound to find the 'best' genetic combination, given enough time for genetic recombination. Adaptation is about organisms within one species outperforming each other. Adaptation can occur without changing the potentially available code to the replicator. Adaptation can be seen as the replicator moving horizontally on the hill.

Mutation downhill is a largely non-reversible, pure chance process. Due to its path dependent chaotic nature it is very hard to predict where it will go. Mutation is about permanent changes in the code available to the replicator, these are changes that affect the species in general. Mutations can open up long avenues of adaptation that life can take at great speed. This could give rise to 'sudden' large changes in a species phenotype. Mutations can be seen as the replicator slipping down the hill.

Both adaptation and mutation happen because changes in the organisms phenotype give it certain advantages over others within the same species. The difference is in whether it takes 'new code' or not.

I think the model of the 'replicator sliding down the hill of replication errors' may give more insight into the cause and effects of sexual reproduction. I would be happy with any comment.
Posted by at

No comments:

Post a Comment

Subscribe to: Post Comments (Atom)
adriaan.bos @gmail.com

Summaries


Laughter and storytelling:

All humans are equipped with the ability to experience the same social emotions like shame, pride, envy and respect. But the applicability of these emotions can vary strongly from group to group and over time. So the brain needs us to constantly calibrate our social morals with those of our group. The most efficient way to do this is through storytelling. We evolved a love of listening to stories, because in a stone age setting that would expose us to the reactions of our group to the story. We slowly but surely mirror the reactions we hear around us, like laughter and outrage, so that we end up in sync with the social morals of the group. This shows why watching comedy without the studio laughter is difficult. Not only can't you laugh with others, you actually get the message that what you hear shouldn't be deemed funny, because nobody else is laughing.

Laughter and storytelling combine to make us compatible in behaviour, because when it comes to social morals, it did not pay to be different. In the modern world, we have automated the storyteller in the middle of the group, into the TV-set we mostly watch on our own. But without the vocal reactions of our group, it might have become a waste of time.


Hunting and gathering.

As humans we solved our basic food problem. Getting the calories we need to survive is easy. But like animals in the zoo that get fed, we have kept much of the display behaviour related to our feeding methods throughout our evolution.

The gatherer into gossip and fashion.
The success in gathering partly depends on the quality of your information network. You need to hear in time where the latest fruiting tree is. There may be more than enough for the person that finds it, but not enough for everyone. A gatherer that finds food will share the information with someone that seems likely to be able to return the favour another time. So gatherers have evolved a need to signal having a quality social network and being 'up to date'.

Gossip and keeping up with fashion trends are modern display behaviours linked to the innate need to be up to date and to be seen to be up to date. With gossip, a gatherer has a special interest in being the first in relaying otherwise useful bits of information.

The hunter into sports and career.
Stone-age hunting is a team effort needing diverse skills. You are better off hunting with a few others. But you do not want to bring anyone along who can't pull his own weight. You do not want to share the meat and the glory with a slacker. So the hunter has evolved a constant need to show they will make a valuable team member to other hunters. That is what gets you on the best hunting party and that gets you the best food and possibly 'extra' mating opportunities.

Every opportunity you have to compete with others to show off your skills can help you get picked by the best. Modern sports and even career are behaviours linked to the need to show you are a valuable team member and you deserve your spot in the highest league. The displays needed to establish and keep your deserved rank would settle down in a small group. In our modern large group the hunter has become stuck in this display behaviour because there is always a higher league to get into. And people's social circle has become more homogeneous through the sorting that happens in school, housing and work arrangements. So there is always someone close ahead or behind. This may be an important driver behind the 'never enough' economy.

Blog Archive