With reference to Biological studies, homology is the presence of shared pedigree between living organisms in terms of evolution. The homology might be in terms of genetical constitution, or physical constitution, to name a few. Here, I have described the evolutionary homology between various phyla supporting the description with a phylogenetic tree.
Genetic code is the combination of DNA and RNA sequences that constitute the amino acid sequences used in the synthesis of an organism's proteins. It is the biochemical basis of heredity and generally, protein coding amino acids is very similar in all eukaryotes and prokaryotes. The principle differences occur in most mitochondrial genomes and certain nuclear genomes (eg. Mycoplasma & Tetrahymena). As the anti-codon is at the opposite end from the amino acid binding site of a tRNA and as it does not interact with the binding site, there is no chemical necessity for a codon to be assigned to a particular amino acid. The genetic code is homologous among living organisms: it is similar despite the fact that there exist many equally good genetic codes. Under my hypothesis that evolution has occurred, however, the similarity among all genetic codes makes sense:
- The common ancestor to all known organisms had a genetic code similar to what we see today.
- Over the ages, the genetic code has passed unchanged (or nearly so) from parents to offspring, because mutations to the genetic code would have been disastrous (changing the amino acid sequence of all proteins produced).
Cytochrome C data Homology:
The cytochrome C complex (cyt c) is a small hemeprotein found attached with the inner membrane of the mitochondrion. It belongs to the cytochrome c family of proteins. Cytochrome c is a highly water soluble protein, unlike other cytochromes. The amino acid sequence of cytochrome c has been analyzed in over 100 eukaryotic species, and the molecular data support the notion that cytochrome c is an evolutionarily conservative protein. Substitutions within the primary structure of cytochrome c are relatively constant over time, which makes characterizing cytochrome c a potentially useful molecular clock. For example, cytochrome c sequence similarity between humans and frogs (91%) is much higher than between humans and e-coli (64%). This indicates that the evolutionary path leading to the human species diverged with that of yeast far before its divergence from rat. A comparison of cytochrome c sequences from different species has been used to order the divergence of species in relative time. The fact that different proteins evolve at different rates makes determining the divergence rate of a particular protein problematic. Also, changes in generation time or metabolic rate may affect a mutation rate, making molecular clocks less predictable. This supports my hypothesis.
Genetic Distances between primates:
Genetic distance is a measure of the genetic divergence between species or between populations within a species. Genetic distance is useful for reconstructing the history of populations. The genome sequences in humans and chimpanzees differ approximately in 35 million single-nucleotide substations. In addition, in result deletion, duplication and insertion, 3% of the complete genome is different. Moreover, as the rate of mutation has been constant, the changes in human lineage hardly can reach one-half of it. And only that small differences resulted in different phenotypes in human and chimpanzee, and therefore, finding those differences is a real challenge. Most of these differences are neutral, and therefore the phenotype cannot be affected. Molecular evaluation has different aspects, protein evaluation, gene loss, differential gene regulation and RNA evolution. All are thought to have played some part in human evolution. A gene can be deactivated in result of different mutations, but rarely they can cause a change of function and in a specific way. Therefore the inactivation mutations are available in any case. Maybe this is how gene loss, has become common mechanism in evolutionary adaptation.
- 80 genes were lost in the human lineage after separation from the last common ancestor with the chimpanzee. 36 of those were for olfactory receptors.
- Genes involved in chemoreception and immune responses are overrepresented.
- In human linage the gene for type I hair keratin is lost. They are one of the essential components in structure of hair. Still nine functional genes in humans belong to type I hair keratin, but still losing that gene might be the reason why human hair became so thin.
- According to Stedman et al. (2004), “the loss of the sarcomeric myosin gene MYH16 in the human lineage led to smaller masticatory muscles. They estimated that the mutation that led to the inactivation (a two base pair deletion) occurred 2.4 million years ago, predating the appearance of Homo ergaster/erectus in Africa. The period that followed was marked by a strong increase in cranial capacity, promoting speculation that the loss of the gene may have removed an evolutionary constraint on brain size in the genus Homo”.
- CASPASE12, a cysteinyl aspartate proteinase. The loss of this gene is speculated to have reduced the lethality of bacterial infection in humans.
- Creation of new primate genes and formation of human genetic variation have been affected by segmental duplications (SDs or LCRs)
The areas of the genome that are different in humans and chimpanzees are called human accelerated regions. And as both species have a common ancestor, explanation by using genetic drift is much more difficult. Basically these regions are proofs of being subject to natural selection, which has led to the distinct traits of human.Two examples are HAR1F, which is believed to be related to brain development and HAR2 (a.k.a. HACNS1) that may have played a role in the development of the opposable thumb. It has also been hypothesized that much of the difference between humans and chimpanzees is attributable to the regulation of gene expression rather than differences in the genes themselves. Analyses of conserved non-coding sequences, which often contain functional and thus positively selected regulatory regions, address this possibility. This finding supports my hypothesis.
Transitional forms and their appearance in geological time scale:
Fish to Amphibian transition: Though it is maintained that fish and amphibians do not have a transitional phase, there have been fossil evidence of the missing links. The link have been constructed as below. (talkorigins.org)
- Paleoniscoids
- Osteolepis
- Kenichthys
- Eusthenopteron, Sterropterygion
- Panderichthys, Elpistostege
- Obruchevichthys
- Tiktaalik —
- Acanthostega gunnari
- Ichthyostega
- Hynerpeton
- Labyrinthodonts
- Gars
- Lungfish and Birchirs
Reptile to Mammal: This class of origination has got transitional phase. Below, the phases of the transition have been elaborated:
- Paleothyris
- Clepsydrops
- Protoclepsydrops haplous
- Varanops
- Archaeothyris
- Dvinia
- Sphenacodon
- Haptodus
- Gypsonictops
- Procynosuchus
- Thrinaxodon
- Exaeretodon
- Cynognathus
- Biarmosuchia
- Probelesodon
- Diademodon
- Oligokyphus
- Probainognathus
- Pachygenelus
- Kayentatherium
- Adelobasileus cromptoni
- Diarthrognathus
- Kuehneotherium
- Eozostrodon
- Sinoconodon
- Morganucodon
- Haldanodon
- Peramus
- Procerberus
- Vincelestes neuquenianus
- Kielantherium
- Asioryctes
- Aegialodon
- Endotherium
- Steropodon galmani
- Pariadens kirklandi
- Kennalestes
- Juramaia
- Sinodelphys
- Eomaia
Reptile to bird transition: This class of origination has got transitional phase. Below, the phases of the transition have been elaborated. (talkorigins.org)
- Allosaurus --A large theropod with a wishbone
- Compsognathus --A small coeleurosaur with a wishbone
- Epidendrosaurus
- Epidexipteryx
- Scandoriopteryx
- Gigantoraptor
- Gobivenator
- Mei
- Saurornithoides
- Sinovenator
- Buitreraptor
- Pyroraptor
- Unenlagia
- Graciliraptor
- Bambiraptor
- Balaur
- Tsaagan
- Dromaeosaurus
- Sinosauropteryx
- Protarchaeopteryx
- Caudipteryx
- Velociraptor
- Deinonychus
- Utahraptor
- Achillobator
- Oviraptor
- Sinovenator
- Beipiaosaurus
- Lisboasaurus
- Sinornithosaurus
- Microraptor –
- Xiaotingia --
- Archaeopteryx
- Anchiornis
- Baptornis
- Rahonavis
- Confuciusornis
- Sinornis
- Iberomesornis
- Theriznosaurus
- Nothronychus
- Citipati
- Falcarius
- Alxasaurus
- Chirostenotes
- Avimimus
- Khaan
- Incisivosaurus
- Caenagnathus
- Troodon
- Byronosaurus
- Ingenia
- Hesperonychus
- Conchoraptor
- Patagopteryx
- Ambiortus
- Hesperornis
- Apsaravis
- Ichthyornis
- Columba One of many typical modern birds
Whales to even-toed hooved mammals transition: This class of origination has got transitional phase. Below, the phases of the transition have been elaborated:
- Ambulocetus-- an early whale that looks like a mammalian version of a crocodile
- Pakicetus -- an early, semi-aquatic whale, a superficially wolf-like animal believed to be a direct ancestor of modern whales.
- Rhodocetus -- An early whale with comparatively large hindlegs: not only represents a transition between semi-aquatic whales, like Ambulocetus, and obligately aquatic whales, like Basilosaurus.
- Basilosaurus -- A large, elongated whale with vestigial hind flippers: transition from early marine whales (like Rhodocetus) to modern whales
- Dorudon -- A small whale with vestigial hind flippers, close relative of Basilosaurus.
- Protungulatum
- Ectoconus
- Hyopsodontidae
- Mioclaenus
- Pleuraspidotherium
- Ernestokokenia
- Phenacodus
- Meniscotherium
- Hyracotherium
Hominid transitions: This class of origination has got transitional phase. Below, the phases of the transition have been elaborated:
- Purgatorius -- the earliest primate-like organism
- Plesiadapis -- Mammal closely related to primates.
- Carpolestes -- Mammal closely related to primates
- Archicebus -- First euprimate, or something very similar to it.
- Omomys -- Tarsier-like organism
- Eosimias -- Basal anthropoid
- Amphipithecus -- Another basal anthropoid
- Apidium -- The first, primitive monkey.
- Propliopithecus -- Primitive New World Monkey
- Darwinius masillae -- a link between earlier primates and later ones.
- Aquatic ape hypothesis — a very controversial suggestion, aquatic apes may or may not have existed
- Australopithecus — a genus of bipedal apes
- Australopithecus sediba — advanced Australopithecus showing more human features
- Homo habilis — a transitional form from Australopithecus to later Homo
- Homo rudolfensis — a type of Homo habilis or a different species
- Homo ergaster — a form of Homo erectus or a distinct species
- Homo erectus — a transitional form from Australopithecus to later Homo (Latin for humans) species
- Homo heidelbergensis — A possible common ancestor of modern man and Homo neanderthalensis
- Homo neanderthalensis — They may or may not have done Humpy bumpy with modern humans.
- Cro-magnon — considered early modern human and perhaps as smart as we are
Geological time in homology:
The Geological time table of evolution given below is in support of my hypothesis.
Phylogenetic tree:
Work Cited:
"Transitional Vertebrate Fossils FAQ Part 1A." Transitional Vertebrate Fossils FAQ: Part 1A. Web. 16 Dec. 2014. .
"Transitional Vertebrate Fossils FAQ Part 1B." Transitional Vertebrate Fossils FAQ: Part 1B. Web. 16 Dec. 2014. .
