How many are there types of animals on Earth? There are so many types of animals including human beings which live in various environments such as land, water and air. All animals possess their different characters according to their living environment, food type, movement, etc. Fishes have fins to swim. Birds have wings to fly. Butterflies have proboscis to drink nectar from flowers. However the characters you see in animals today are very different from those of animals living in the past. WHY?
Why are the characters found in animals today different from those of animals living in the past?
All animals including human beings were descended from their ancestors.
Scientists described that Australopithecus is a group closely related to and often considered ancestral to modern human beings. This group appeared in East Africa approximately 4.4 million years ago and had a combination of humanlike and apelike characters, with long arms, curved fingers and shorter legs (https://www.britannica.com). There are many differences between this group of human ancestor (Plate 1) and modern human beings.
Plate 1 Human ancestor lived from 3.8 to 2.9 million years ago
This group of human ancestor adapted to their living environment changed due to various factors and resulted in the changes of characters. These changes took place slowly over time until the development of the characteristics we see in human beings today. Thus animals alive today have developed from their ancestors through the process of biological change that is called evolution. The descendants come to differ from their ancestors by this process of evolution.
Patterns in Evolution
- Convergent Evolution
Different unrelated species living in similar environmental conditions adapt to their living environment. Therefore they have similar characters although they are different unrelated species.
Example: dolphins and sharks. They are different unrelated species because dolphins are mammals and sharks are fish. They live in water and adapt to their similar environmental conditions. They have both evolved similar tail fins (Plate 2) to propel themselves through the water. The tail fins of dolphins are horizontal and used for up-and-down motion. The tail fins of sharks are vertical and used for side-to-side motion.
This evolution (biological change) toward similar characteristics (tail fins) in unrelated species (dolphins and sharks) is called convergent evolution.
Plate 2 Similar tail fins of dolphin and shark
- Divergent Evolution
Divergent evolution is a different pattern of convergent evolution.
Closely related species living in different environmental conditions adapt to their living environment. Though closely related, the two species have different characters.
Example: kit fox and red fox. They are closely related species because they have common ancestor (Plate 3). They live in different environmental conditions to which they adapt. Thus they have evolved different characters.
Kit fox lives in deserts and has sandy-coloured coat and large ears relative to its body size. Its sandy-coloured coat allows it to blend in with its desert surroundings and large ears help it to keep cool in the desert heat. Red fox lives in temperate forests and has dark reddish coat which helps it to hide from predators.
This evolution (biological change) toward different characters (sandycoloured coat and large ears in kit fox; dark reddish coat in red fox) in closely related species (kit fox and red fox) is called divergent evolution.
Plate 3 Kit fox (left), red fox (centre) and their common ancestor (right)
Differences between two patterns in evolution
The differences observed between two patterns in evolution are summarized in Table 1.
Table 1 Summary of differences between two patterns in evolution
|No.||Convergent evolution||Divergent evolution|
|1||Different unrelated species||Closely related species with common ancestor|
|2||Live in similar environmental conditions||Live in different environmental conditions|
|3||Adapt to similar environmental conditions||Adapt to different environmental conditions|
|4||Evolution toward similar characteristics||Evolution toward different characteristics|
Adaptation plays an important role in the process of evolution. Some species are unable to adapt to various environments and became extinct.
Some species are capable of being adapted to various environments and have evolved their new characters. They have a better chance of surviving and reproducing. Thus new species have evolved on Earth.
Author- Htet Htet
Module Zool. 623 Evolutionary Biology and Aimal Behaviour