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Comparing the anatomy of different organisms has been key to providing evidence for evolution by looking at homologous, analogous, homoplastic and vestigial structures.
If the organisms found today had come into existence independently there would be more differences than similarities, but related species have similarities that lay the foundation of examining relationships between them and revealing a common origin.
Comparative anatomy is often the first step in studying the similarities and differences or relationships between anatomical structures of animal groups and determining relationships between species. It is not too complicated, and no technology is needed. However, technology should be used in conjunction with comparative anatomy in determining evolutionary relationships between species.
Comparative anatomy can provide strong evidence for evolution by constructing a morphological series but in my opinion, it is inconclusive and must be supported and tested by other studies such as in genetics, molecular studies and palaeontology, especially in the modern world where it is available. Evolutionists need to track the changes through time and look further than the superficial, external or visible structures of organisms present today to determine their common descent and relatedness.
Some external or visible structures that can be compared to provide evidence for evolution:
Homologous structures – as in morphological series
Forelimb of mammals
The same basic design and structure of bones and soft tissue in the forelimb of mammals, although slightly different in shapes, sizes and function but this provides evidence that this basic design had been inherited from a common ancestor. The forelimbs became specialized or modified from this ancestor over time into that which is found in the mammals today. These mammals found unique ways to survive and use their limbs in a different way with different functions, but the basic design leads to the inference that all mammals descended from one organism. This basic design can be seen in the human, bird, lion and seal which all have a humerus, forearm, wrist and digits although these are used differently by them.
The reduction of horse digits over time from 4 digits to a single digit.
Gill bars or arches of fish which gave rise to the jaws of other vertebrates.
The hip and shoulder bones of fish and the early tetrapod which have similarities in their basic design.
The bird’s wing and mole’s arm reveal common decent from a reptilian ancestor.
Analogous structures – the same function, but not necessarily the same origin
The wings of bats, birds and bees evolved independently and look similar on the outside but function similarly in giving the organism the ability to fly.
The forelimbs of turtles and dolphins function similarly by using them as paddles.
Reveals convergent evolution
Homoplastic structures – look the same, but not necessarily homologous or analogous
The flippers of turtles and dolphins which look alike, function similarly and reveal common descent.
Mimicry or camouflage in palatable and unpalatable butterflies.
Can also be compared to other organisms such as the whale hip and hindlimb that has been reduced over time and no longer used but which is like that in tetrapod ancestors. This reveals that at some point whales had been using four legs.
Determining evolutionary relationships using comparative anatomy alone can be useful in identifying basic and derived characteristics but these superficial similarities do not always point to a common ancestor. Using the support of other evidences, genetics, molecules and palaeontology, would only strengthen the validity of biological evolution.
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