A Simple Idea About the Cambrian Explosion

Different parts of this idea when working with my hybrids have been gnawing at me for quite some time. Working at the loom or spinning gives me time to let my mind wander and finally a picture came into focus...

From all I've read, pre-Cambrian fossil evidence suggests mostly single celled (or nearly so) lifeforms. For simplicity's sake let's say that at this time their chromosomes would resemble a simple "X". There really wouldn't be a need for more since replication is a matter of duplicating and dividing. At some point just prior to the Cambrian era one or more of these chromosomes doesn't separate. It's now "XX" but still happily making copies of itself.

Some time later two things may have come together... The oxygen levels in sea and air have been building from so many little lifeforms replicating and consuming carbon dioxide and one or more of those little "XX" things loses a leg becoming "XY". Look familiar? (Could this be that pesky "rib"?)

All of a sudden, the option of producing more lifeforms exists via sex. There is a trade-off... instead of being essentially clones and existing forever, each unique new individual, when it dies, is replaced by others who may be similar but not exactly the same and evolution begins.

Imagine what would happen with the reshuffling of genes over and over among these individuals. The key to the explosion of forms may be simply that because not enough inbreeding within closely related groups has yet occurred to produce species, there is no species barrier.

It's possible that until pockets of similar individuals begin to breed exclusively within their group all forms have enough in common to reproduce and an "explosion" of new lifeforms is the result. This could be why nothing like the "Cambrian Explosion" has been seen since and probably won't be seen again unless life begins from "scratch".

Once individuals begin breeding more or less exclusively within their own group, similar genetic traits would assert themselves and the "species barrier" would go up. (This is the step where Mendel's ideas about inheritance can be applied.) Fertility within each group would likely improve but there's another trade-off. Over time each lifeform would pass along good and bad traits without the benefit of being able to pull in new genes to increase the vigor of the population. As each group becomes more specialized, inbreeding would slowly give each form a unique character. As individuals die off and the population becomes more genetically alike, this would also send each form on the inevitable path to extinction.

Since life still exists on this planet, it's a simple step to think the ideal safety net for species on shaky ground would again be hybridization. If under enough environmental stress, species find the means to cross and produce even small numbers of similar individuals the whole race for these new species to find their niche begins. If not, they wind up as fossils under someone's microscope or stuffed in some museum.

If true, a scenario like this could explain a lot. :-)