From the vegetable LUCA to current days and the future. Science blog 118th
In the previous instalment of this blog, we explained Charles Darwinâ€™s idea on the existence of common ancestor to all current forms of life.
By observing such idea, we are of the opinion that this common ancestor must have vegetable characteristics and may come from a primal DNA molecule with the capacity to form a surrounding membrane out of local material, vacuolize such membrane and form a functional ribosome. We also exposed the state of our experimentation in these phases.
This brings us from current days to the origin of life on Earth, since a confirmation of this hypothesis allows us to travel the inverse path, that is from the origin of life to current species in its current forms. To follow the reasoning of how life has evolved on Earth, we will take Ernest Haeckel (Potsdam, 1834 â€“ Jena, 1919) and Richard Dawkins (Nairobi, 1941) as reference.
In Ernest Haeckelâ€™s work General morphology of organisms (1866) the first tree of life was drawn, placing the current species at the end of the branches and the ancestors closer to the trunk. This implies that, from the current genetic perspective, modern living forms are far more specialized and, therefore, more vulnerable to environmental changes.
This characteristic of specialization is also pointed out by Richard Dawkins: “Evolution by natural selection is a very simple idea. For thousands of generations, in a struggle for existence, advantageous variations have managed to survive. It is a process that shapes life to transform it into more specialized ways.”
For a few years, we were investigating wild canary genetics and the formation of the 324 varieties of colored canary derived from the wild bird. Using the terminology “predecessor”, we could say that the wild canary is the common ancestor of all colored canaries. The green-black color of the plumage and its sexual dimorphism directly depend on 8 genes:
- 2 autosomes that regulate the intestinal absorption of yellow and red carotenes
- 2 autosomes that regulate blue and brown melanin synthesis
- 2 sexual genes regulating the deposit of blue and brown melanin in the feathers
- 2 sexual genes regulating the deposit of yellow and red carotenes in different feather areas
If it stops producing or fixing brown melanin the Agate canary variety is obtained, when blue melanin is not produced, then the Isabela variety is obtained. In contrast, if no melanin is produced canaries will be either yellow, orange or red. In addition, when carotenes are not absorbed, we obtain white canaries. Such combinations can go on up to 324 different varieties.
Our conclusion is that, as Dawkins says, “life is transformed into more specialized forms”. This implies the reduction of functions by selection pressure. In other words, natural selection is a destructive force since the surviving forms are more specialized and, at the same time, more vulnerable. For this reason, species tend to become extinct due to the pressure of several episodes of selection.
If we consider natural selection as a destructive force, we are pushed through to consider the existence of a creative force. It is in the balance of both creative and destructive forces where the new life forms would originate. In the words of Heraclitus of Ephesus: “Perhaps nature […] disposed by means of opposites […] conforms a primordial harmony”. The question that arises is: what is the positive force that opposes the negative force of natural selection?
In our opinion, such force is composed by the genes that can be activated by an external physical, mineral, vegetable stimulus or by self-regulation â€“ genetic duplication allows the fixation of a particular cellular or biochemical function in a locus, so that the duplicated locus remains free to play a new role.
This positive force would add some feature that would provide the ability to survive,Â regardless of the disappearance of non-adapted forms. Adding a new feature can only be achieved if there is a previous genetic instruction. For example, the transformation process from fish to amphibian requires the formation of a complex bone structure in the legs and it is not possible to relate the disappearance of non-adapted fish species with the expression of genes that allow the formation of the bones.
Thus, genetics make it possible, perhaps following an activation program or in response to new stimuli, but not because of the disappearance of species – a fact that does not seem to matter to nature.
What will happen in the future? Genetics will continue to propose new possibilities and natural selection will keep eliminating those that are no longer adapted to new environmental conditions.