In science, the concept of the unity of the origin of life on Earth is considered fundamental. And so a discovery that applies to one of its forms can be applied to all others. Thanks to which, by the way, the functions of many internal human organs were studied and methods for treating dangerous diseases were developed.
Examples of similar and homologous organs
It is impossible, however, based on the relationship of all life on earth, to mix homologous and similar organs. The former have the same structure and develop from the same embryonic rudiments, 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 performs the same function in both insects and birds. But in insects, these are chitinous protrusions on the surface of the back, and in birds, they are forelimbs that have changed in the process of evolution. The same parallel can be drawn between the gills of a dragonfly larva and a fish.
The eyes of a human and an octopus can also be defined assimilar bodies. Despite their resemblance, they absolutely
different in structure. The lens of the human eye is fixed, and the eye itself is an outgrowth from the rudiment of the brain. While in the octopus, the organs of vision are formations from the body cover, in which the lens of the lens approaches or moves away from the retina, aiming at the object of attention of the animal in order to establish the correct focus.
Examples of analogy can be seen even among pigments such as hemoglobin and hemocyanin. They carry oxygen equally, but their molecular structure is very different.
Rudiments
In their own way, atavisms and rudiments confirm the theory of the origin of life.
The latter include, as a rule, those organs that do not fulfill their original function, having lost it in the process of evolution. But it is impossible to consider all rudiments absolutely useless. They just often do less important things.
Thus, for example, the wings of an ostrich can be defined as vestigial organs, because they do not cope with the main task of the bird's wing, but are used by it to attract females and to maintain balance while running. Thus, the complexity of the structure of this organ is inadequate to the simplicity of the task it performs. This is a sign of a rudiment.
But the wing of a penguin cannot be considered as such, since it performs a rather complicated function as a fin.
The rudiments include the eyes of a mole and a mole rat, which or nothing at alldo not see, or only distinguish between darkness and light.
In humans, this characteristic has tail vertebrae, muscles that
helped our ancestors to raise their fur and muscles to move their ears. Everyone knows another human rudiment - a process of the caecum (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, a tail-like process in humans or hind fins in a dolphin.
The appearance of atavisms can be explained by the presence of genes responsible for this trait in DNA. But they have not been functioning for a long time, as their action is suppressed by other genes.
Homologous and similar organs, rudiments and atavisms - all this is an undoubted confirmation of the unity of the origin of life of creatures inhabiting the Earth.
