Class 10 | Easy notes on Heredity and evolution | Evidences of evolution

Evidences Of Evolution 

Evidences of evolution :

1. Morphological evidences

2. Anatomical evidences 

3. Vestigial organs

4. Paleontologic evidences

5. Connecting links

6. Embryological evidences 

1. Morphological evidences

In animals Various similarities like structure of mouth, position of  eyes, structure of nostrils and ear pinnae and thickly distributed hairs on body are seen.

In plants similarities in characters like leaf shape, leaf venation, leaf petiole, etc. occur.

This indicates that there are some similarities in those groups and hence it proves that their origin must be same and must have common ancestors.

2. Anatomical evidences 

Superficially there is no similarity observed in between human hand, cat’s foreleg, flipper of whale and patagium of bat. Also use of each of those structures is different in respective animals. However, there is similarity in structure of bones and bony joints in organs of each of those animals.This similarity indicates that those animals may have common ancestor.

3. Vestigial organs

• Degenerated or underdeveloped useless organs of organisms are called as vestigial organs.

• A specific structure in the body is useful under certain situation.However, same structure under different situation may become useless or even harmful.

• [ Some organs begins to degenerate under such situation as per the principle of natural selection. It takes thousands of years for a structure to disappear. Such organs are seen in different phases of disappearance in different animals ].

• Vestigial organs may be non-functional in certain organism, but it may be functional in other organisms i.e. it is not vestigial in other organisms.

• eg. i)  Appendix is useless to human but it is useful and fully functional organ in ruminants.

ii) Muscles of ear pinna, which are useless to human, are useful in monkeys for movement of ear pinna.
iii) Other examples - tail-bone (coccyx), wisdom teeth, and body hairs are present in body of human being.

4. Paleontologic evidences

• Fossils : Large number of organisms get buried due to disasters like flood, earthquake, volcano, etc. Remnants and impressions of such organisms remain preserved underground. These are called as fossils.

• Study of fossils is an important aspect of study of evolution.

• Carbon Dating : 

• Carbon consumption of animals and plants stops after death and since then, only the decaying process of C-14 occurs continuously.

• In case of dead bodies of plants and animals, instead of remaining constant, the ratio between C-14 and C-12 changes continuously as C-12 is non-radioactive.

• The time passed since the death of a plant or animal can be calculated by measuring the radioactivity of C-14 and ratio of C-14 to C-12 present in their body. This is ‘carbon dating’ method. 

Use : Carbon dating is used in paleontology and anthropology for determining the age of human fossils and manuscripts. 

5. Connecting links

Some plants and animals show some morphological characters by which they can be related to two different groups; hence they are called as ‘connecting links’. 
Eg. i) Peripatus

• Peripatus show characters like segmented body, thin cuticle, and parapodia-like organs similar to annelida.

• Similarly, these animals show tracheal respiration and open circulatory system similar to arthropods.

• This indicates that Peripatus is connecting link between annelida and arthropoda.
  

ii) Duck billed platypus

Duck billed platypus lays eggs like reptiles also it has mammary glands and hairs like mammals.
This indicates that Duck billed platypus is connecting link between reptiles and mammals. 

iii) Lung fish 

• Lung fish performs respiration with lungs irrespective of being fish.
• Lungfish is a connecting link between fishes and  amphibians.
  
• These examples indicate that mammals are evolved from reptiles and amphibians from fishes.

6. Embryological evidences

all embryos show extreme similarities during initial stages and those similarities decrease gradually. Similarities in initial stages indicate the common origin of all these animals.