In science, the concept of the unity of the origin of life on Earth is considered fundamental . And so the discovery, which is applicable to one of its forms, can be attributed to all the others. Due to this, by the way, the functions of many internal organs of a person were studied and methods for treating dangerous diseases were developed.
Examples of similar and homologous organs
It is impossible, however, based on the kinship of all life on earth, to mix homologous and similar organs. The former have the same structure and develop from the same embryo embryos, confirming the unity of origin (for example, the five-fingered limb of different animal species). But similar organs, often performing the same function in different animals, have different rudiments.
A common example of such cases is the wing. It has the same function in insects and birds. But in insects, these are chitinous protrusions on the surface of the back, and in birds - the forelimbs, modified in the process of evolution. The same parallel can be drawn between the gills in dragonfly larvae and fish.
The eyes of a person and an octopus can also be defined as similar organs. Despite the resemblance, they are absolutely
different in structure. The lens of the human eye is fixed, and the eye itself is an outgrowth of the primordium of the brain. Whereas in an octopus, the organs of vision are the formation from the cover of the body in which the lens of the lens approaches or moves away from the retina, pointing at the object of attention of the animal to establish the correct focus.
Examples of analogy can be considered even among pigments such as hemoglobin and hemocyanin. They equally carry oxygen, but their molecular structure has great differences.
Rudiments
Atavisms and rudiments confirm the theory of the origin of life in their own way.
The latter include, as a rule, those organs that do not fulfill their original function, having lost it in the process of evolution. But all rudiments cannot be considered absolutely useless. They simply often perform less important actions.
So, for example, ostrich wings can be defined as rudimentary organs, because they do not cope with the main task of the bird's wing, but are used by them to attract females and to maintain balance during running. Thus, the complexity of the structure of this organ is inadequate to the simplicity of its task. This is a sign of rudiment.
But the wing of the penguin can not be considered as such, since it performs a rather complex function as a fin.
Rudiments include mole and mole rat eyes, which either do not see anything at all, or only distinguish between darkness and light.
In humans, the tail vertebrae, muscles that have
helped our ancestors to raise their fur, and muscles to move their ears. Everyone knows another human rudiment - the appendix of the
cecum (appendix).
Atavisms
When an individual has signs characteristic of its distant ancestors, this phenomenon is called atavism. For example, the appearance in some people of a continuous hairline on the body or an additional pair of mammary glands, the caudate process in humans or the posterior fins in a dolphin.
The appearance of atavisms can be explained by the presence of genes responsible for this trait in DNA. But they no longer function for a long time, since their action is suppressed by other genes.
Homologous and similar organs, rudiments and atavisms - all this is an indisputable confirmation of the unity of the origin of life of creatures that inhabit the Earth.