Many living things have identical (or homologous) structures. This homology proves that they evolved from each other. It also proves that evolution occurred because the structure has been selected due to its advantage to the organism.
The Facts Are .....
Comparative anatomy has been used as proof of evolution, however there is little value in the argument today. The discovery of parallelism (similar or identical characters in different species) must not be interpreted to mean that both species came from the same ancestor. Parallelism is no longer regarded as evidence for evolution by the world's most respected palaeontologists. Scientific Monthly, Vol. 16, No. 3, 1923 p:246; Albert S. Romer, "Genetics, Paleontology and Evolution", (Glen S. Jepson ed.), Princeton University Press, 1949 p:115
The bill on a platypus and a duck are examples of homologous structures. In homology, the genes that produce the structure are said to have been passed on to successively evolving organisms.
This theory breaks down, and the 'proof' for evolution disappears, when it is noted that many so-called homologous structures like these are produced by entirely different genes. Scott M. Huse, "The Collapse of Evolution", Baker Book House: Grand Rapids (Michigan), 1983 p:116-117
The front appendages of reptiles, mammals, birds and humans are said to be homologous
‘proving’ that they come from a common ancestor. The facts are, however, that these appendages are not homologous structures because they are not produced by the same genes. If one organism evolved from another, and maintained a certain structure, then they must maintain the same genes that produced that structure. This is necessary because it is the genes which control all the characteristics of an organism. In the lizard, the foreleg develops from the 6th-9th embryo segment.
For others, they develop from:- Salamander (2nd-5th), Frog (2nd-4th) and Swift (10th-14th).
Likewise for the hind leg:- Lizard (25th-30th), Salamander (16th-18th), Frog (8th-10th) and Swift (20th-27th). Sir Gavin de Beer, "Homology, an Unsolved Problem", Oxford Biology Reader, 1971
"..... what mechanism can it be that results in the production of homologous organs, the same
'patterns', in spite of their not being controlled by the same genes? I asked this question in 1938, and it has not been answered." Written by Sir Gavin de Beer, one of the great embryologists of this century in his monograph "Homology, An Unsolved Problem", Oxford Biology Reader, 1971
"The known presence of parallelism in so many cases and its suspected presence in others suggests that it may have been an almost universal phenomenon." Albert S. Romer expressing the view that the existence of so many organisms with similar structures may not be due to evolution, but part of the characteristics of all living things. Written in Glen S. Jepson (ed.),
"Genetics, Paleontology and Evolution", Princeton University Press, 1949 p:115
"My last doubt concerns so-called parallel evolution ..... Even something as complex as the eye has appeared several times; for example, in the squid, the vertebrates, and the arthropods. It's bad enough accounting for the origin of such things once, but the thought of producing them several times makes my head swim." Written by Frank B. Salisbury in his article "Doubts About the Modern Synthetic Theory of Evolution", in American Biology Teacher, September, 1971 p:336-338