There are many genes that have been discovered which regulate embryonic development in animals. Similar versions of some of these genes are found in different phyla where they regulate similar structures that are thought to have "evolved" independently. These homologous genes that regulate analogous structures might encourage the Darwinist to reconsider whether those structures might actually be homologous due to common ancestry. However, in consideration of the evidence that the animal phyla do not have common ancestors, these "homologies of process" are better explained as evidence of intelligent design, where the designer reused the same control mechanism for the development of similar structures in unrelated organisms.
Examples of structures that evolved independently but are controlled by the same genes include:
- The anterior-posterior axis in vertebrates and flies.1
- The vertebrate and insect eyes.1
- Gastrulation in vertebrates and insects1
- The insect and vertebrate hearts.1
- The nematode vulva, the mammalian epidermis, and the Drosophila terminal segments.1
- The body axes and limbs in vertebrates and drosophila.1
- "Mammals, urochordates, sea urchins, insects, annelid worms, and onycophorans, all use a similar regulatory gene to control limb growth. But they have radically different types of limbs, making this either a case of radically extreme "convergent evolution" or simple common design."2
Resynthesizing Evolutionary and Developmental Biology
Resynthesizing Evolutionary and Developmental Biology
Scott F. Gilbert,*,1 John M. Opitz,† and Rudolf A. Raff‡
Three major groups (E. B. Lewis and D. S. Hogness in California; W. Gehring in Basel; T. Kaufman in Indiana; and their respective students) used the new molecular techniques to isolate and sequence these genes, and they discovered a remarkably stable region: a 180-bp consensus sequence called the ‘‘homeobox.’’ It appeared that the genes responsible for homeotic transformations were themselves homologous.
These genes were said to be homologous, and since the homeotic genes appeared to create the anterior–posterior axis in flies, it was speculated that the same genes might create the anterior–posterior axis in humans. To some, this idea seemed bizarre.
In the 1990s, the use of homologous recombination to functionally delete homeotic genes in mice enabled numerous laboratories to see what happened when vertebrates lacked one or more of these genes. The results demonstrated that these genes controlled the formation of the anterior–posterior axis in vertebrates as well as in flies
The segmentation of Drosophila and the segmentation of vertebrates had been a classic example of analogy. Yet, here it was seen as being directed by a homologous set of genes.
The insect eye and the vertebrate eye are two examples of structures said to be analogous. However, they can be shown to both be based on the expression of the Pax-6 gene (Quiring et al., 1994), and it is probable that the vertebrate and insect (and cephalopod) eyes are the modified descendents of a basic metazoan photoreceptive cell that was regulated by Pax-6.
Similarly, the Xenopus gene chordin and the Drosophila gene short-gastrulation have similar sequences and expression patterns, and they act similarly in vertebrate and insect gastrulation (to counter the lateralizing effects of BMP-4/decapentaplegic). Even though the types of gastrulation do not appear similar to any marked degree, the genes controlling them may be homologous (Francois and Bier, 1995; Holley et al., 1995). Similarly, the heart of vertebrates and the heart of insects have hardly anything in common except their ability to pump fluids. Yet, they both appear to be predicated upon the expression of the same gene, Csx/tinman (see Manak and Scott, 1994).
[The] same system has been found to exist in the determination of the nematode vulva, the mammalian epidermis, and the Drosophila terminal segments. The similarity in these systems is so striking that many of the components are interchangeable between species. The gene for human GRB2 can correct the phenotypic defects of sem-5-deficient nematodes, and the nematode sem-5 protein can bind to the phosphorylated form of the human EGF receptor (see Greenwald and Rubin, 1992; Gilbert, 1994b). The process is thus historically (specifically) homologous between species (Drosophila retina/nematode vulva) and serially homologous within species (Drosophila retina/Drosophila acron and telson).
In vertebrates, there are several homologues to wingless, namely, the wnt proteins; the homologue to zest-white 3 is glycogen synthase kinase 3b (GSK-3b); and there are numerous hedgehog analogues, such as sonic hedgehog. In vertebrates, the wingless–hedgehog system is thought to be needed for producing the body axes (as in Drosophila) and the limbs (as in Drosophila).
Recently, several laboratories have shown that the same proteins that generate the insect leg also generate the vertebrate limbs.
Few people would have expected that a similar situation would exist for another embryological field—the vertebrate limb field. After all, here is the classic example of analogy as opposed to homology. The insect and vertebrate legs share the same function, but that’s about it. The insect leg forms from the telescoping of the ectodermal imaginal disc. The vertebrate limb forms from the reciprocal induction of the Apical Ectodermal Ridge, the mesodermal Progress Zone mesenchyme, and the mesodermal Zone of Polarizing Activity.
This section is particularly illustrative of why evolutionary biology is really just a house of cards:
The insect eye and the vertebrate eye are two examples of structures said to be analogous. However, they can be shown to both be based on the expression of the Pax-6 gene (Quiring et al., 1994), and it is probable that the vertebrate and insect (and cephalopod) eyes are the modified descendents of a basic metazoan photoreceptive cell that was regulated by Pax-6.A basic metazoan photoreceptive cell is only "probable" if you assume insects and vertebrates had a common ancestor. But the evidence shows that there is no common ancestor to vertebrates and insects and so there cannot be a common ancestor (a basic metazoan) that had a photoreceptive cell. But evolutionists assume that all animals have a common ancestor and then they use that to explain observed phenomena. As these explanations accumulate they claim evolution is supported by masses of evidence... but that evidence is based on assuming what they are trying to prove.
Another interesting point is that these regulatory genes have been so highly conserved over hundreds of millions of years that some are interchangeable between phyla, yet they are responsible for embryonic development in animals that are supposed to have evolved during that time. Species are different because they develop as embryos differently. These differences are not just differences between phyla but between species within phyla. If differences between phyla and species within phyla are due to evolution, one should expect to find differences in the genes that control embryonic development. However, if organisms were designed, one would expect to see identical parts used in different systems.
One of the evolutionist explanations for the Cambrian explosion is that new genetic information was not needed because the changes in body plan were caused by changes in regulatory genes. That seems doubtful given that regulatory genes seem to be so highly conserved that some are interchangeable between phyla.
Yet ironically, the last section of the article includes this:
The homologies of process within morphogenetic fields provide some of the best evidence for evolution.
In fact, the homologies of process provide some of the best evidence for intelligent design.
- Casey Luskin at evolutionnews.org writes:
But the case for intelligent design in limb-bud controlling genes gets stronger when one realizes that the same regulatory genes are used to control limb growth in organisms far more diverse than vertebrates: mammals, urochordates, sea urchins, insects, annelid worms, and onycophorans, all use a similar regulatory gene to control limb growth. But they have radically different types of limbs, making this either a case of radically extreme "convergent evolution" or simple common design. (See Paul Nelson and Jonathan Wells, "Homology in Biology," in Darwinism, Design, and Public Education (Michigan State University Press, 2003), pg. 316.) As plant geneticist from the Max Plank Institute, Wolf-Ekkehard Lönnig, wrote in Dynamical Genetics, "No theorist in evolutionary biology will ever derive chicken and insects from a winged common ancestor, and yet, clearly related sequences are specifically expressed in wing buds and imaginal disks."