Creation 34(4):43–45, October 2012
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Homology made simple
Have you ever noticed the many similarities that exist between different animals? Many animals have two eyes, two ears, four limbs, a heart, a brain, five digits (fingers and toes), etc. The natural world is full of these kinds of patterns and evolutionists have a special term for them. They call them ‘homologies’ or ‘homologous organs’ or ‘homologous structures’. Homologies simply refer to similarities which, according to evolutionists, are due to their being inherited from a common ancestor.
So, according to evolutionists, the eyes of the different animals on the bottom row of fig. 1 are ‘homologous organs’ because they inherited them from a common ancestor that had eyes. Similarly, the legs of these animals are ‘homologous structures’ because they allegedly inherited them from a common ancestor that had legs. So, referring again to the diagram in fig. 1, frogs, seals, birds and people are said to possess eyes and legs because they inherited them from a common ancestor that looked something like the one at the top.
If you open a typical biology textbook that teaches evolution you will probably find diagrams like the ones in figs. 2–3. They show the similarities between the forelimbs (front legs or arms) of various animals. Each has a humerus shown in green, a radius shown in blue, an ulna shown in brown and digits shown in yellow. Evolutionists, of course, argue that there is a very straightforward explanation for these similarities—they were inherited, they say, from a common evolutionary ancestor. The forelimbs, they claim, are an excellent example of homology. Perhaps more than anything else, this kind of diagram has convinced many people that evolution is true. However, as with all arguments for evolution, when we scratch beneath the surface, we find that the argument collapses. Let’s see how this one collapses when it’s subject to scrutiny.
The secrets of embryos
Humans and frogs both have digits—that is, fingers, thumbs and toes. Now if humans and frogs have digits because they inherited them from a common ancestor, we would expect their digits to grow in a similar way. We would expect the embryonic development of the digits in humans and frogs to be basically the same, the same as in the common ancestor from which they are allegedly descended. But digit development in humans and frogs is different.
With reference to fig. 4, in humans we start off with a spade-like structure and the digits—the fingers and toes—develop through the material between them dissolving away. The material between the digits is removed. (That’s how your fingers developed when you were in your mother’s womb.) In frogs it’s different. The digits grow outwardly and independently from buds. The material is added.1 If evolution were the correct explanation for why humans and frogs both have digits, we would expect their embryonic development to be similar—we would expect humans and frogs not only to have inherited the digits but because the similarity is supposed to be due to shared genes, also the same process of digit development. Interestingly, limb development varies even between one amphibian and another, for example between frogs and salamanders.2 What is so significant about all this is that these are not isolated examples. The embryonic development of so-called homologous structures is often different—and not just with respect to limbs.
As far back as 1894, the American embryologist Edmund Wilson wrote, “It is a familiar fact that parts which … are undoubtedly homologous, often differ widely … in [their] mode of formation.”3
Moreover, according to the late Spanish embryologist Dr. Pere Alberch, it is ‘the rule rather than the exception’ that homologous structures develop differently.4
Homology—a big problem for evolutionists
Sir Gavin de Beer was one of the foremost embryologists of the 20th century. He was a Fellow of the Royal Society, and went on to become the Director of the Natural History Museum in London. In 1971 he wrote a paper which he titled, Homology: an Unsolved Problem.5 Now Gavin de Beer was an evolutionist, he believed in Darwin’s theory of evolution; but he couldn’t reconcile this with the facts of embryology. In his paper he gave examples of homologous structures that developed in very different ways, from different parts of the egg or embryo and under the control of different genes. It was a mystery to him because it flew in the face what he expected to find as an evolutionist; hence the title of his paper calling homology ‘an unsolved problem’. He never solved this problem—and nor has anyone else.
Gunter Wagner is Professor of Ecology and Evolutionary Biology at Yale University. Speaking of this same problem, the problem of reconciling the facts of embryology with the theory of evolution, he wrote, “The disturbingly many and deep problems associated with any attempt to identify the biological basis of homology have been presented repeatedly.”6(Emphasis added.)
Now they tell the youngsters in the schools and the students in the universities that evolution is the great unifying principle in biology. They tell us that Darwin explained the diversity of life. The celebrated evolutionist Theodosius Dobzhansky assured us that “nothing in biology makes sense except in the light of evolution.” But this is simply not true. The reality is that attempts to reconcile the facts of biology with Darwin’s theory give rise to many and deep problems.
A creationist interpretation of homology
So what are we to make of all the similarities? Why do so many animals have two eyes, two ears, a heart, lungs etc? Why are the forelimbs so similar in different animals? Why is the natural world so full of these kinds of patterns? Well, normally, when people see a pattern they assume there must have been a designer; and in the absence of a satisfactory evolutionary explanation, strong patterns in nature surely point to just that—a designer, a creator. Common anatomy unifies the natural world and points to there being just one creator. There aren’t many gods and many creators, who have made radically different life forms from fundamentally different parts. There is one God—the Creator—and His creation reflects this.7
Homology and homoplasy
Rather than providing support for evolution, patterns of similarity seen throughout the living world, in addition to providing evidence for a single designer (see main text), actually resist naturalistic explanations, as the widespread occurrence of homoplasy indicates. To explain; quite often, animals have similar organs or structures which, in the thinking of evolutionists, cannot be explained by common ancestry. A good example is the ‘camera-eye’ which has a lens and retina, a design found in both humans and octopuses (see fig. 5). Since humans and octopuses are not thought to have inherited their eyes from a common ancestor, these are not regarded as homologous. Instead, evolutionists would refer to them as an example of homoplasy. This is also known as ‘convergent evolution’ because it is understood that the evolutionary process has ‘converged’ upon the same design independently. There are numerous examples of alleged homoplasy.8 Bats and dolphins both have echolocation systems that work in a similar way to man-made sonars.9 Some fish generate electricity, which they use to stun prey or ward off attackers, an ability that has supposedly evolved independently six times.10 Similarly, tuna and mako sharks both move their tail fin with strong red central muscles attached to the fin with tendons. Yet in evolutionary terms, they could not have gained this (unusual for fish) mechanism from a common ancestor.11 The likelihood of evolutionary processes producing this level of similarity, based on chance mutations filtered by selection in randomly varying environments, seems very remote. Eyes are believed by some researchers to have evolved independently some sixty different times.12
Placentals (e.g. humans) are mammals whose young develop internally, in their mother’s womb, nourished through a placenta. Marsupials (e.g. kangaroos) are mammals that carry and suckle their young externally in a pouch. According to the theory of evolution, placentals and marsupials evolved from a common ancestor that looked a bit like a modern shrew. These early placentals and marsupials allegedly then evolved into many different animals. What is so difficult for evolutionists to explain, however, is why, in so many cases, placentals evolved almost identical forms to marsupials (see fig. 6).
Many plants produce food and grow using energy from the sun, through a complex process called ‘photosynthesis’. One form of this is named ‘C4 photosynthesis’ and is particularly complex. Because of the differences between the plants that use the C4 process, evolutionists again have to argue that this evolved independently more than thirty times.13,14 It seems mind-boggling that a process of such complexity could have evolved once; but to claim that this happened so many times stretches credibility beyond all reason. It requires a lot of blind faith to be an evolutionist!
Also, sometimes structures alleged to be homologies must be explained away as homoplasies when the evolutionary family tree is changed. For example, based on supposedly homologous features in their skulls and teeth, whales were dogmatically proclaimed to have evolved from mesonychids, an extinct type of large predatory ungulate (animal with hooves). But DNA similarities convinced evolutionists that they evolved from another group—artiodactyls (‘even-toed’ ungulates), similar to the hippopotamus. So these supposedly definitive homologies must be re-interpreted as homoplasies.
Evidence for evolution?
Evolutionists say that similarities undeniably point to common ancestry. But this is clearly not true, as has been shown, because close similarity is frequently found in creatures where evolutionists concede that common ancestry cannot be the explanation. Despite this, evolutionists even define homology as ‘similarity due to common ancestry [i.e. evolution]’. At the same time, homoplasy is defined as ‘similarity due to [convergent] evolution’. Hence, in the thinking of evolutionists, similarity with common ancestry is evidence for evolution, and similarity without common ancestry is evidence for evolution. Whatever similarity they find, then, is evidence for evolution!
‘Homoplasy’ is no more than terminology masquerading as an explanation. The concept of homoplasy is not derived from scientific evidence but from blind faith. This faith rests upon the arbitrary assumption that natural processes can explain everything—including rampant ‘convergence’, however improbable this might appear.
References and notes
- In humans, the digits develop through apoptosis (programmed cell death) but in frogs through cell division at the growth points. See Futuyma, D., Evolutionary Biology, Sinauer Associates, Massachusetts, USA, 2nd ed., p. 436, 1986. Return to text.
- Fröbisch , N.B., and Shubin, N.H., Salamander limb development: Integrating genes, morphology, and fossils, Developmental Dynamics 240:1087–1099, 2011. See also Statham, D.R., Problems with the evolutionary interpretation of limb design, J. Creation 26(2):10, August 2012. Return to text.
- Wilson, E.B., The Embryological Criterion of Homology, in Biological Lectures Delivered at the Marine Biological Laboratory of Wood’s Hole in the Summer Session of 1894, Ginn & Co., Boston, USA, pp. 101-124, 1895. ia600402.us.archive.org/25/items/biologicallectur1894mari/biologicallectur1894mari.pdf. Return to text.
- Alberch, P., Problems with the interpretation of developmental sequences, Systematic Zoology, 34(1):46-58, 1985. Return to text.
- De Beer, G., Homology: an Unsolved Problem, Oxford University Press, UK, 1971. Return to text.
- Wagner, G., The origin of morphological characters and the biological basis of homology, Evolution 43(6):1163, 1989. Return to text.
- Furthermore, in most cultures that have existed, including the biblical one, such a pattern of commonality would bring honour to a Designer, by demonstrating authority over and mastery of His designs. See Holding, J.P., J. Creation 21(1):13 –14, 2007; creation.com/original. Return to text.
- Conway Morris, S., Life’s Solution: Inevitable humans in a lonely universe, Cambridge University Press, UK, 2005. See review by ReMine, W., Evidence for message theory, J. Creation 20(2):29–35, 2006. Return to text.
- Ref. 8, p. 181. Return to text.
- Ref. 8, p. 183. Return to text.
- Nature 429 (6987):31–33, 61–65, 2004. Return to text.
- Fernald, R.D., Eyes: variety, development and evolution, Brain, Behavior and Evolution 64(3):145, 2004, cited in Bergman, J., Did eyes evolve by Darwinian mechanisms? J. Creation 22(2):67–74, August 2008; creation.com/eyes-evolve. Return to text.
- Ref. 8, p. 293. Return to text.
- Batten, D., C4 photosynthesis—evolution or design?, J. Creation 16(2):13–15, August 2002. Return to text.
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