Convergent vs Divergent Evolution
When considering living organisms, evolution can be defined as the development of differentiated organisms from less differentiated pre-existing organisms over the course of time. There are many sources, which provide evidence to the theory of evolution. They are palaeontology, geographical distribution, classification, plant and animal breeding, comparative anatomy, adaptive radiation, comparative embryology and comparative biochemistry.
What is Divergent Evolution?
When a group of organisms has a homologous structure, which is specialized to perform a variety of different functions, it shows a principle known as adaptive radiation. For an example, all the insects share the same basic plant for the structure of the mouthparts. A labrum, a pair of mandibles, a hypopharynx, a pair of maxillae, and a labium together forms the basic plan of the mouthparts structure. In certain insects, certain mouthparts are enlarged and modified, and others are reduced and lost. Due to this they can utilize a maximum range of food material. This gives rise to a variety of feeding structures. Insects show a relatively high degree of adaptive radiation. This shows the adaptability of the basic features of the group. This can also be called the evolutionary plasticity. This has enabled them to occupy a wide range of ecological niches. A structure present in an ancestral organism becomes greatly modified and specialized. This can be called a process of descent by modification. The significance of adaptive radiation is that it indicated the existence of divergent evolution, which is based on the modification of homologous structures over time.
What is Convergent Evolution?
Structures and physiological processes can be similar in organisms, which are not closely phylogenetically related and they may show similar adaptations to perform the same function. These are referred to as analogous. Some examples for analogous structures are eyes of vertebrates and cephalopods, wings of insects and birds, jointed legs of vertebrates and insects, thorns on plants and spines on animals etc. Similarities found in analogous structures are only superficial. For example, insect wings and wings of bats and birds are analogous structures. However, the wings of the insects are supports by veins composed of cuticle and the wings of birds and bats are supported by bones. In addition, vertebrate eyes and cephalopod eyes are analogous structures. But the embryological development of the two is different. Cephalopods have an erect retina, and photoreceptors facing the incoming light. In contrast, in vertebrates, the retina is inverted and the photoreceptors are separated from the incoming light by the connecting neurons. Therefore, the vertebrates have a blind spot and the cephalopods do not have a blind spot. Convergent evolution is supported by the presence of analogous structures.
What is the difference between Convergent Evolution and Divergent Evolution?
• Divergent evolution is supported by the homologous structures, and the convergent evolution is supported by the analogous structures.
• Divergent evolution occurs in phylogenetically related organisms, and convergent evolution occurs in organisms, which are not closely phylogenetically related.
• All the homologous structures bear the same basic plan of the structure whereas the analogous structures are just superficially related.