Evolution by natural selection is as close to a fact as you can possibly get. It’s a scientific theory; that is, it’s backed up by objective, falsifiable, empirical evidence – it’s not simply a ‘guess’ or an ‘idea’ or ‘just a theory’ – scientific theories aren’t colloquial ‘theories’. This is why every national academy of science and scientific organisation which has made a statement on the evolution-creation “controversy” has been fully supportive of the theory of evolution. The InterAcademy Panel, for instance, consisting of more than 100 national science academies, endorsed the following statement:
Since its first appearance on Earth, life has taken many forms, all of which continue to evolve, in ways which palaeontology and the modern biological and biochemical sciences are describing and independently confirming with increasing precision. Commonalities in the structure of the genetic code of all organisms living today, including humans, clearly indicate their common primordial origin.
Meanwhile, in 2005, the National Science Teachers Association, a professional association made up of 55,000 science teachers, said of Intelligent Design – the only alternative “hypothesis” there is to evolution:
intelligent design is not science… it is simply unfair to present pseudoscience to children in the science classroom
In the same year, 38 Nobel Laureates issued a statement stating the following:
intelligent design is fundamentally unscientific; it cannot be tested as a scientific theory
Finally, it’s worth noting that at least 47 of the Nobel Prize winning bodies of work for medicine or physiology have depended on evolutionary theory, demonstrating its importance within science. (1)
In a nutshell, this shows that there is no debate in the scientific community over evolution by natural selection, and this is because of the evidence coming from at least 6 different independent scientific fields in support of evolution. Firstly, we’ll start off with the fossil evidence. Fossils are valuable, although not necessarily essential, in learning about the tree of life and they demonstrate that, over time, organisms have changed and become more complex, and are related to each other. To take a specific example, we can look at the fossil record of the horse – we start with Eohippus, or Hyracotherium, which was a small animal, the size of a fox, and we can then look at all of the intermediate species that existed between Eohippus and the modern horse – equus, and find that various features have changed – a 45 inch increase in size, the lengthening of the limbs and feet and the reduction of lateral digits, for example. (2) The earliest of these changes occurred during the transition of eohippus to orohippus, approximately 50 million years ago, which evolved an elongated head, slimmer forelimbs and longer hind legs, which increased its proficiency in jumping. (3) In sum, with this example, we can see that over millions of years, eohippus has gradually, going through at least 12 different transitional species in the process, evolved into the modern horse.
When it comes to fossils, a common complaint that one might hear from religious people who deny evolution is that “missing links” have not been found; that is, the exact common ancestor of two certain groups or species. Firstly, this is axiomatically incorrect because a number of “missing links” or intermediate forms have been found. But, secondly, their insistence upon this demonstrates their misunderstanding of evolution. The fact of the matter is that as long as we find transitional forms that fit with the predictions of evolution, we will know that the prediction is correct. For example, biologists do not think they have yet found the exact common ancestor of birds and reptiles, but they have found fossils of a number of birds who have reptilian features, and vice-versa, which demonstrates that birds do share a common ancestor with reptiles. One of the earliest known birds which also had reptilian features was archaeopteryx, which lived around 150 million years ago. (4) This, and many other fossils like it, demonstrates that birds share a common ancestor with reptiles and that groups of animals were different in the past. There is also an abundance of fossils in support of human evolution, specifically common ancestry with chimpanzees, for example the famous Homo erectus and Homo habilis, as well as Australopithecus afarensis, a species which lived between 3 and 4 million years ago and had a number of human characteristics, including arches in the foot (5) but also many characteristics of a chimpanzee, including the smaller sized brain.
Evidence also comes from molecular biology and genetics. All living organisms have been found to share DNA in common and the genetic record corroborates the fossil record in that we see the same tree of life – the fossils, for example, suggest that apes are the closest cousins to humans, and that is exactly what we see in the DNA record, with chimpanzees being our closest cousins sharing 98.8% of DNA with us. (6) This shows that humans and chimpanzees are related and share a common ancestor. Not only that, but pseudo genes also rule out design as an explanation for the genetic observations – we share non-functional DNA with other organisms as well as functional DNA (7), but seeing as this DNA has no use, why would an intelligent designer even insert it into our genetic code in the first place, especially as some estimates have it as making up 99% of our genetic code. A specific chromosome illustrates nicely our common lineage with chimpanzees and other hominids, namely chromosome 2. This is because hominids, including chimpanzees, have 24 pairs of chromosomes, yet humans only have 23 pairs of chromosomes. The cause of the missing chromosome is that human chromosome 2 is a fusion of two ancestral chromosomes, and this is supported by the fact that chromosome 2 in humans has a near identical DNA sequence to that of two separate chromosomes in chimpanzees (8), demonstrating that those two separate chromosomes fused together to form human chromosome 2. Of course, those in the intelligent design community might argue that the intelligent designer simply used the same DNA that was in the two chimpanzee chromosomes but decided to put it in only one chromosome in humans instead. Not only does this seem incredibly far-fetched and have no evidence whatsoever to support it, but the presence of vestigial telomeres also supports the ancestral fusion model – telomeres are usually found at the ends of chromosomes, yet in chromosome 2, they’re also found in the middle, showing that two ends of our ancestral chromosomes fused together to form human chromosome 2. (9) This is why the biologist J.W. Ijdo concludes:
the locus cloned in cosmids c8.1 and c29B is the relic of an ancient telomere-telomere fusion and marks the point at which two ancestral ape chromosomes fused to give rise to human chromosome 2
Would an intelligent designer literally fuse together two chromosomes? Again, it seems unlikely, but I’m sure creationists could concoct some kind of scenario in which an intelligent designer would do this. This is exactly why scientists regard intelligent design as pseudoscience – it’s unfalsifiable. Chromosome fusion, by contrast, is an observed phenomenon in biology.
More evidence from molecular biology in support of evolution by natural selection comes from cytochrome C, which is a ubiquitous protein which exists in all living cells of every organism and performs very basic life functions. It is made up of 100-104 different amino acids, in a sequence, and as expected, similar organisms have similar or identical sequences of cytochrome C: for instance, humans and chimpanzees have identical sequences as do chicken and turkeys, as do pigs cows and sheep. Meanwhile, rhesus monkeys’ sequences are identical to humans and chimpanzees’ except for one amino acid. (10) This is, of course, strong evidence, but it’s even stronger evidence for common ancestry because the protein cytochrome C has a high degree of functional redundancy; that is, changing the amino acid sequence barely affects the functionality of the protein, meaning that it’s far more likely that humans and chimpanzees, for example, share an identical sequence due to random mutation and common ancestry rather than due to an intelligent designer, because an intelligent designer could have made the sequence identical in every single organism and it wouldn’t have affected how it worked! Only random mutation would, for no reason, alter the sequence when no alteration was needed.
Moving into comparative anatomy, there is a plethora of evidence that supports evolution by natural selection. To take a specific example, the recurrent laryngeal nerve in, especially, giraffes, provides evidence that giraffes’ ancestry lies in the ocean and that intelligent design is, again, false. The recurrent laryngeal nerve, rather than travel an optimal route of just several inches, takes almost a 15 ft detour by passing from the brain down into the neck, past the heart, round the aorta and through the neck again to the larynx. Natural selection explains this perfectly – the nerve’s route would have been direct in the fish-like ancestors of modern tetrapods, traveling from the brain, past the heart, to the gills (as it does in modern fish). Over the course of evolution, as the neck extended and the heart became lower in the body, the laryngeal nerve was caught on the wrong side of the heart. Natural selection gradually lengthened the nerve by tiny increments to accommodate, resulting in the circuitous route now observed. (11) However, there’s no reason at all to suggest a reason as to why an intelligent designer would create such a professedly illogical route for a nerve.
Perhaps the most obvious evidence for evolution by natural selection is the fact that it has been observed. One of many examples is Dr. Richard E. Lenski’s long-term experiment with e.coli. He started off with 12 identical populations of asexual e.coli, and by changing the environments in which the populations were living, induced many evolutionary adaptations in them due to beneficial random mutations. Other observations include the evolution of elephants – ivory hunters obviously kill elephants with larger tusks, which means that smaller-tusked individuals may be at an evolutionary advantage. And, that’s exactly what we see – the Uganda Game Department, for example, published data showing that, over just 3 decades, the average tusk size of the elephants, most likely due to ivory hunting, decreased, as elephants who had smaller tusks had a larger chance of reproducing. Another observation of evolution before our very eyes is the case of Italian wall lizards – in 1971, biologists moved five adult pairs of Italian wall lizards from their home island of Pod Kopiste, in the South Adriatic Sea, to the neighboring island of Pod Mrcaru. Decades later, Duncan Irschick, a professor of biology at the University of Massachusetts Amherst says that “striking differences in head size and shape, increased bite strength and the development of new structures in the lizard’s digestive tracts were noted after only 36 years, which is an extremely short time scale.” This was directly because of the change in the environment that the lizards were living in – observed changes in head morphology were caused by adaptation to a different food source. (12) According to Irschick, lizards on the barren island of Pod Kopiste were well-suited to catching mobile prey, feasting mainly on insects. Life on Pod Mrcaru, where they had never lived before, offered them an abundant supply of plant foods, including the leaves and stems from native shrubs. As a result, Professor Irschick observed that “individuals on Pod Mrcaru have heads that are longer, wider and taller than those on Pod Kopiste, which translates into a big increase in bite force… Because plants are tough and fibrous, high bite forces allow the lizards to crop smaller pieces from plants, which can help them break down the indigestible cell walls.”
The geographical distribution of animals also illustrates how much better the explanatory power of evolution by natural selection is compared to creationism or ID. For instance, kangaroos and other marsupials are only found in Australia, an observation that can easily be explained by evolution by natural selection. By contrast, according to creationism, there was a massive flood 4000 years ago which wiped out every organism on the planet bar two of each kind. After the flood was over, the animals disembarked from the Ark in the Middle East. So, why did all the kangaroos go to Australia? And, why do we not find a single fossil of a kangaroo anywhere between the Middle East and Australia?
1. James McCarter, “Evolution is a Winner – for Breakthroughs and Prizes”, National Center for Science Education, originally published in the St. Louis Post-Dispatch, 2005-10-09.
2. MacFadden, B. J. (1999), Fossil Horses: Systematics, Paleobiology, and Evolution of the Family Equidae. Cambridge & New York: Cambridge University Press. ISBN 0-521-47708-5
3. MacFadden, B. J. (1976). “Cladistic analysis of primitive equids with notes on other perissodactyls”, Syst. Zool 25 (1): 1–14. Doi: 10.2307/2412774. JSTOR 2412774
4. Alan Hamilton Turner, Peter J. Makovicky and Mark Norell (2012). “A review of dromaeosaurid systematics and paravian phylogeny”, Bulletin of the American Museum of Natural History 371: 1–206 doi:10.1206/748.1
5. Ward, C. V.; Kimbel, W. H.; Johanson, D. C. (2011). “Complete Fourth Metatarsal and Arches in the Foot of Australopithecus afarensis”. Science 331 (6018): 750.
6. Chen FC, Li WH (2001). “Genomic Divergences between Humans and Other Hominoids and the Effective Population Size of the Common Ancestor of Humans and Chimpanzees”, American Journal of Human Genetics 68 (2): 444–56.
7. Petrov DA, Hartl DL (2000). “Pseudogene evolution and natural selection for a compact genome”, J Hered, 91 (3): 221–7.
8. Yunis and Prakash; Prakash, O (1982). “The origin of man: a chromosomal pictorial legacy”. Science 215 (4539): 1525–1530
9. Ijdo, J. W.; Baldini, A; Ward, DC; Reeders, ST; Wells, RA (1991). “Origin of human chromosome 2: an ancestral telomere-telomere fusion”. Proceedings of the National Academy of Sciences 88 (20): 9051–5.
10. Lurquin PF, Stone L (2006). Genes, Culture, and Human Evolution: A Synthesis. Blackwell Publishing Incorporated. p. 79, ISBN 1-4051-5089-0
11. Dawkins, Richard (2009). The Greatest Show on Earth: The Evidence for Evolution. Bantam Press, pp. 364–365. ISBN 978-1-4165-9478-9.
12. Dawkins, Richard (2009). The Greatest Show on Earth: The Evidence for Evolution. Bantam Press, pp. 113-114. ISBN 978-1-4165-9478-9; see also Johnson, K, “Lizards Rapidly Evolve after Introduction to Island”, National Geographic, April 21st 2009.