GENETIC EVIDENCE FOR EVOLUTION

MODEL 1:  The various groups of living things are not related because they did not evolve from a common ancestor. Humans have not descended from other primates.

Because their origins were completely independent, any pattern of similarity could be observed (including no similarities whatsoever) when comparing their molecules and the same pattern of similarity need not be observed consistently. 

MODEL 2: Living things have evolved from a common ancestor; humans have evolved from other primates.  Not only should relationships be evident when their molecules are compared (close similarity for those whose last common ancestor lived recently; a more distant relationship for those whose last common ancestor was more distant).  The same general pattern of similarity should present itself for most genes, proteins, and even non-coding DNA.

 

WHICH OF THESE TWO MODELS IS SUPPORTED BY THE GENETIC EVIDENCE?

      We can compare the molecular makeup of different living things.  We can compare the general types of molecules found (proteins, lipids, etc.), amino acid sequences in proteins, overall DNA similarity (DNA hybridization), chromosome banding, gene order on chromosomes, nucleotide sequences of nuclear genes, nucleotide sequences of genes found in small cellular organelles, and nucleotide sequences of noncoding regions of DNA have no affect on the traits of an organism.  If evolution did not occur, there are a number of patterns we could observe: all the molecules could be the same (there could only be one vertebrate hemoglobin sequence, for example), the molecules could completely different from each other (each vertebrate could have its own oxygen carrying molecule other than hemoglobin), or there could be variations which do not present any consistent pattern.

      If evolution has occurred, we expect to see the relationships observed in the cladograms in the molecular evidence and these relationships should be fairly consistent no matter what molecule is used.  Which of these two models does the evidence support?


 

When the gene sequences of mitochondrial cytochrome oxidase II are compared (Ruvulo, 1994), there are variations in the sequences found in humans, in chimps, in gorillas, in orangutans, and in gibbons.  While humans may not all have the same sequences, their sequences are more similar to each other than any one is to the sequence of any other ape.  For that reason, all humans seem to be related, that is, they are descended from the same ancestors and their gene sequences are modifications of the same ancestral sequences.  In the same way, each species of chimpanzee contains sequences that are related to each other and the same can be said for gorillas, orangutans, and gibbons.  Similarities can be extended above the species level.  The two species of chimpanzee seem to be closely related to each other, that is, both species are descended from the same ancestors.  Human and chimp sequences are more similar to each other than they are to any other ape (or animal, for that matter).  Not only do chimps seem to be the closest relatives of humans, humans seem to be the closest relatives of chimps.

     Notice that the evidence suggests a hierarchy of similarities—the variation between species is merely an extension of the variation within a species.  Most of those who oppose evolution would agree that the two species of chimp have evolved from a common ancestor but that humans are completely unrelated to them.  Some have written that chimps, gorillas, and orangutans have descended from a common ancestor but that humans are completely unrelated to them.   This creationist pattern—that one can identify “kinds” which are equally unrelated to each other and in which humans are separated from other animals—is simply not observed.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 



The same general pattern of relationship is observed when the sequence of a nuclear gene is examined (28S rRNA; Gonzalez, Mol. Biol. Evol. 7: 203-219; 1990).

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HUMAN         CHIMPANZEE          GORILLA      ORANGUTAN         

 

 

 

 

 

 

 

 

 

 


The same general pattern of relationship is observed when noncoding DNA which does not contribute to an organism’s phenotype is used.

 

HUMAN         CHIMPANZEE          GORILLA      ORANGUTAN         

 

 

 

 

 

 

 

 

 


--yhglobin upstream and downstream flanking regions; Miyamoto, 1987.

 

 

 

HUMAN         CHIMPANZEE          GORILLA      ORANGUTAN         

 

 

 

 

 

 

 

 

 

 


--noncoding DNA sequence data;Williams, Mol. Biol. Evol. 6: 325-330, 1989


 

Other studies show that apes are more closely related to each other than any of them is to any Old World monkey.

HUMAN         CHIMPANZEE          GORILLA      ORANGUTAN          GIBBON          OWM

 

 

 

 

 

 

 

 

 

 

 

 

 


--DNA-DNA hybridization; Sibley, J. Mol. Evol. 20: 2-15

--various old world monkeys yield same relationship (Allenopithecus nigroviridis, Papio hamadryas, Macaca mulatta, Pygathrix nemaeus, Cercopithecus aethiops)

 

Apes and Old World monkeys are more closely related to each other than any of them are to New World monkeys.  Some creationists have written that all Old World monkeys could have evolved from a common ancestor, that New World monkeys could have evolved from those of the Old World, and that the higher apes (other than humans) are related.  There is no support for a separate origin of humans or of equally non-related groups within primates given the genetic evidence.

 

APES                    OWM: colobines        OWM: cercopithecines       NWM

 

 

 

 

 

 

 

 

 

 

 

--lysozyme gene sequences; Messier, 1997.

Apes branches indicate human, 2 chimp species, gorilla, orangutan, and gibbon; the two subfamilies of old world monkeys are shown.

 

 


HUMAN         CHIMPANZEE          GORILLA                  OWM                    NWM

 

 

 

 

 

 

 

 

 

 

 

 


--MHC Class II genes; Edwards Genetics 146: 655-668; 1997.

 

 


HUMAN         CHIMPANZEE          GORILLA      ORANGUTAN                OWM         NWM

 

 

 

 

 

 

 

 

 

 

 

 

 

 


--alpha galactosyltransferase; Galili Proc. Natl. Acad. Sci. 88: 7401-4; 1991.

 

Apes, Old World monkeys, and New World monkeys are all more related to each other than any of them is to a lemur (a prosimian primate).   All primates are more closely related to each other than any is to any other mammal.

 

HUMAN         CHIMPANZEE          GORILLA      ORANGUTAN    OWM    NWM   LEMUR

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


--h globin ; Koop; Nature 319: 234-7.  1986.

 

 


Primates are not the only placental mammals whose genetic sequences suggest that they are related.  Not only do dolphins and whales seem to be descended from a common ancestor, they share a common ancestor with the even-toed hoofed mammals (artiodactyls), having evolved from primitive artiodactyl ancestors.  Interestingly, the fossil evidence also indicates the whales are descended from artiodactyls.

 

ARTIODACTYLS, WHALES, AND DOLPHINS

 

 

 

 

 

 

 

 

 

 

 


--rRNA sequences; Messenger, 1998.  (the five branches on left are artiodactyls; all the remaining branches represent whale and dolphin species)


The combined data of 314 molecular phylogenies indicates that not only do placental mammals include groups which are related to each other through a common ancestry, all placental mammals are descended from a common ancestor (Liu, 2001).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 



Molecular comparisons indicate that crocodilians are the closest living relatives of birds.  The fossil evidence indicates the same relationship: birds and crocodilians are the only surviving archosaurs.

 

BIRDS                                   Allligator

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


12S and 16S rRNA; Hedges, 1995. (rhea is the branch at the far right of the birds)

 

Molecular evidence supports that higher vertebrates evolved from amphibians which in turn evolved from sarcopterygian fish.  The same pattern is indicated by the fossil record.

 

Human     mice        frogs             sarcopterygian fish     actinopterygian fish

 

 

 

 

 

 

 

 

 

 

 


--28S rRNA sequence; Zardoya, 1996. (sturgeon is branch on far right)

 

 

 


The jawless fish are the most basal vertebrates; all other vertebrates are more closely related to each other than any are to jawless fish. (Goodman J Mol Evol 17: 114-20; 1981).

 

Gnathostome myoglobin with Jawless Fish Hemoglobin

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Molecular comparisons indicate that all animals are related by common descent.

Goodman, 1988, Globin

 

Jawless

 Fish

 

Mollusc

 

 

Arthropods

 

Annelids

 

Plants

 

Human

 

 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


 

 

 


PROTOSTOMES                                        Deuterostome           Cnidarians

 

 

 

 

 

 

 

 

 

 

 

 

 

 


18S rRNA sequences, Aguinaldo, 1997.

Chordates         Echinoderms                           PROTOSTOMES

 

 

 

 

 

 

 

 

 


--18S rRNA; Lake1990 (chordates are human, frog, lancet, tunicate)

 


Molecular comparisons indicate that all eukaryotes (animals, fungi, plants, and protists are related).

 

Elongation Factor 2 (after King, 2001) (Humans first branch on left)

Animals

 

Fungi

 

Protists

 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


a tubulin (after King, 2001)

Animals

 

Fungi

 

Protists

 

Plants

 

Protists

 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


 

 

 


Actin (after King, 2001)

Animals

 

Fungi

 

Protists

 

Plants

 

Protist

 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


MAMMALS              BIRDS  REPT.  AMPH  FISH   INVERT    PLANT   FUNGI

 

 

 

 

 

 

 

 

 

 

 

 

 


--cytochrome c sequence; Fitch

 


Not only are all eukaryotes related, all living things (eukaryotes and prokaryotes) are related.  Of the two groups of prokaryotes, archebacteria and eubacteria, most molecular comparisons indicate that the archebacteria is more closely relate to the eukaryotes.

 

PHYLOGENY BASED ON ELONGATION FACTOR EF-G/2

Baldauf 1996

 

 

 

 



ANIMALS      FUNGI       PLANTS        PROTISTS           BACTERIA

 

 

 

 

 

 

 

 

 

 


--amino acid sequences of 57 enzymes; Feng, 1997. 

 

 

Deuterostomes    Protostomes    Pseudocoel.    Fungi     Plants   Protists    Archebact.   Eubact.

 

 

 

 

 

 

 

 

 


--amino acids of 57 enzymes; Doolittle, 1996.


Animals    Plants    Fungi     Protists               ARCHAEA                          EUBACTERIA

 

 

 

 

 

 

 

 

 

 


Morell, 1997; based on Woese

 

EUKARYOTES                                  ARCHAEA                              EUBACTERIA                       

 

 

 

 

 

 

 


--rRNA, Pace, 1986.  (humans on far left)

 

 

 

 

 

 

 

 

 

IleRS gene sequence; Brown, 1995. (humans far left branch)

 

EUKARYOTES                                  ARCHAEA                              EUBACTERIA

 

 

 

 

 

 

 

 

 

 

 



     In the creationist model, there are groups of living things (which they call “kinds”) which are related by common descent.  All kinds however, are equally unrelated to each other.  There is no reason that a pattern suggesting a nested hierarchy of relationships should present itself since no group has any special relationship with any other group.  Some creationists argue that animals which are superficially similar would naturally be expected to be more similar genetically.  There are two main reasons why this argument is inadequate.  First of all, the molecules which are used for comparisons are selected because they perform similar functions in the animals being compared (this is actually a requirement for a molecular comparison—if natural selection has acted on a molecule in one lineage differently than in another, the resulting branch patterns will differ from other sequence comparisons).  The traits which make humans more superficially similar to apes than to other mammals are not determined by rRNA sequences, alpha hemoglobin sequences, cytochrome c sequences, etc.

     Secondly, using such a creationist hypothesis, one might predict that all monkeys would be most related to each other molecularly (molecular comparisons do not support this: Old World monkeys are more closely related to apes than New World monkeys).  One might predict that the higher apes would be most related to each other molecularly (molecular comparisons do not support this: humans and chimps are more closely related to each other than either is to any other ape).  One might predict that placental mice or flying squirrels would be most similar to marsupial “mice” and “flying squirrels”; the molecular evidence does not support this.  One might predict that all artiodactyls would form a clade that would exclude whales; the molecular evidence does not support this.  One might predict that all fish would be expected to form a clade; the molecular evidence indicates that sarcopterygian fish are more closely related to amphibians than they are to bony fish.  One would not predict the observed relationship between birds and crocodilians or archebacteria and eukaryotes.  One might predict a relationship between snakes and legless lizards, bats and birds because they both fly (and bats are even classified as birds in some biblical passages and some creationists have argued that they should continue to be classified as such), all worm-like animals, etc.; none of these predictions would be supported by molecular comparisons.

     Molecular sequence comparisons overwhelmingly support the nested hierarchy pattern of relationship predicted in the evolutionary model.  Not only is such a pattern observed, it is the same pattern that is observed in the analysis of anatomical, embryological, and fossil evidence.