Gastrula and metamers formation (homonomous or heteronomous) are two processes that organize the future individual tissues longitudinally and transversely starting from a single cell.

This double segmentation is common in all current animals (including annelids, fish, amphibians, reptiles, birds and mammals) except sponges, and is run by a genetic sequence almost unchanged in the last 600 million years. From here we can trace the origin of the different organs up to the first animals that presented each one of them, from the eyes to the skeletal system (endoskeleton).

We can even venture looking for the origin of the formation of multicellular organisms from a primitive cell called Last Universal Common Ancestor (LUCA) and go backwards until the formation of the first cell by the foreign cytoplasm process.

In Veterinaria Digital we have posted 15 blogs devoted to the origin and evolution of existing organs:

No. 3 (anapsids, diapsids and therapsids), No 5 (from Alcoveria brevis to land animals), No. 8 (heart muscle evolution), No. 9 (stomach evolution), No. 10 (kidney evolution), No. 13 (the origin of the eye and the Central nervous system), No. 14 (the origin of the liver), No. 15 (the origin of the pancreas), No. 16 (the origin of the hypophysis), No. 17 (brainstem ganglia chain, the origin of the cranial pairs), No. 18 (liver and bladder ligaments, and its evolutive significance), No. 19 (the origin of the skeletal system), No. 28 (phylogenetics and regeneration of the adult brain), No. 35 (the origin of the eye-2 example for phylogenetic dating and nutrition), No. 36 (extremities development origin metagenetics), No. 46 (origin of the endocrine system); as well as 10 blogs about the origin of life No. 1 (From Oparin to Venter), No. 20 (Reflections about the hypothesis of the last universal common ancestor), No. 27 (the origin of life from Antiquity to synthetic biology), No. 33-1st (the origin of life and its beginnings on Earth), No. 33-2nd (hypothesis of primitive RNA and panspermia), No. 33-3rd (protobiontic chemosynthetics), No. 40 (advanced Panspermia), No. 41 (Oparin’s abiogenic hypothesis), No. 42 (neocreationist hypothesis) and No. 43 (outer cytoplasm hypothesis).

This blog of Disclosure in Veterinaria Digital is dedicated to Haeckel's tree (see picture) as a graphical explanation of a process about which we now know the biochemical and genetical aspects. Ernst H.P.A. Haeckel was born in Potsdam on February 16th 1834 and died in
Jena on August 9th 1919. Getting ahead of the current knowledge Haeckel argued that all organisms (animals, plants and unicellular organisms) came from a single ancestral form (now called LUCA) and that the state of "gastrula" was common in all metazoa, formed by an invagination of the blastula.
From his observations Haeckel considered necessary to design, in 1866, what today is known as Haeckel’s tree of life. This is a genealogical tree of the species where he exposes what would be the species origin of a new species.
Seeking common ancestors we find the reason why species apparently very remote in time and geography, share embryonic processes and structures of common organs.

In this blog of disclosure (XLVII) we want to expose the entailment between the origin of life, Haeckel’s tree and the origin of the organs:
(1) We start from a basic molecule of RNA or DNA, coupled to a capsule, capable of being expressed according to the metagenetic mechanisms.
(2) This basic structure can originate the last universal common ancestor, which would be located at the base of Haeckel’s tree.
(3) The formation of various organelles by the mechanism of outer cytoplasm (disclosure No. 43) would give rise to plant, animal or protist cells, that would be located in the first branches.
(4) Following the branch that leads to the vertebrates we see that in a very early stage of evolution occurs the conjunction in the gastrulation formation, as a longitudinal ordination system, with segmentation or vertebration as a transversal ordination system that will later share annelids and vertebrates.
(5) Longitudinal ordination evolution explains the origin of the digestive system and the attached glands, while the transversal ordination explains the origin of the nervous system, endocrine system and lymphatic system among others.

In Veterinaria Digital we believe that the study of the genetic mechanisms of segmentation and metagenetic mechanisms of expression, via the relationship between plant and animal cells, can lead to important advances in disease prevention (malformations, degenerative, infectious, parasitary and derived from nutrition diseases), as well as a great approximation to the origin and evolution of life from the first molecules to current complex organisms and finally present an hypothesis on a folded molecule that has been unfolding, over time, in contact with the outside elements by metagenetic mechanisms giving rise to new organs and therefore new species whose existence was scheduled, since it seems improbable that the random addition of genetic material can result in an organ with a specific function.