29+ Evidences for Macroevolution The Scientific Case for Common Descent Version 2.85 Copyright © 1999-2004 by Douglas Theobald, Ph.D. [Last Update: undefined NaN, NaN] Permission is granted to copy and print these pages in total for non-profit personal, educational, research, or critical purposes. Introduction volution, the overarching concept that unifies the biological sciences, in fact embraces a plurality of theories and hypotheses. In evolutionary debates one is apt to hear evolution roughly parceled between the terms "microevolution" and "macroevolution". Microevolution, or change beneath the species level, may be thought of as relatively small scale change in the functional and genetic constituencies of populations of organisms. That this occurs and has been observed is generally undisputed by critics of evolution. What is vigorously challenged, however, is macroevolution. Macroevolution is evolution on the "grand scale" resulting in the origin of higher taxa. In evolutionary theory it thus entails common ancestry, descent with modification, the genealogical relatedness of all life, transformation of species, and large scale functional and structural changes of populations through time, all above the species level (Freeman and Herron 2004; Futuyma 1998; Ridley 1993). Common descent is a general descriptive theory that concerns the genetic origins of living organisms (though not the ultimate origin of life). The theory specifically postulates that all of the earth's known biota are genealogically related, much in the same way that siblings or cousins are related to one another. Thus, macroevolutionary history and processes necessarily entail the transformation of one species into another and, consequently, the origin of higher taxa. Because it is so well supported scientifically, common descent is often called the "fact of evolution" by biologists. For these reasons, proponents of special creation are especially hostile to the macroevolutionary foundation of the biological sciences. This article directly addresses the scientific evidence in favor of common descent and macroevolution. This article is specifically intended for those who are scientifically minded but, for one reason or another, have come to believe that macroevolutionary theory explains little, makes few or no testable predictions, is unfalsifiable, or has not been scientifically demonstrated. Outline Introduction Part I. A unique, historical Part 2. Past history phylogenetic tree ● Universal Common 1. Anatomical vestiges Descent Defined 1. Unity of life 2. Atavisms ● Evidence for Common 2. Nested hierarchies ❍ Whales with Descent is 3. Convergence of hindlimbs Independent of independent phylogenies ❍ Humans tails Mechanism ❍ Statistics of 3. Molecular vestiges ● What Counts as incongruent 4. Ontogeny and Scientific Evidence phylogenies developmental biology ● Other Explanations 4. Transitional forms ❍ Mammalian ear for the Biology ❍ Reptile-birds bones, reptilian ● How to Cite This ❍ Reptile-mammals jaws Document ❍ Ape-humans ❍ Pharyngeal ❍ Legged whales pouches, ❍ Legged seacows branchial arches Scientific Evidence and the 5. Chronology of common ❍ Snake embryos Scientific Method ancestors with legs ❍ Embryonic human tail Phylogenetics ❍ Marsupial introduction eggshell and caruncle 5. Present biogeography ● Figure 1: A consensus 6. Past biogeography universal phylogeny ❍ Marsupials ● Cladistics and ❍ Horses phylogenetic ❍ Apes and humans reconstruction ❍ Maximum parsimony ❍ Maximum likelihood ❍ Distance matrix methods ● Statistical support for phylogenies ● Does phylogenetic inference find correct trees? ● Caveats with determining phylogenetic trees Part 3. Evolutionary Part 4. Molecular evidence Part 5. Change opportunism 1. Protein functional 1. Genetic 1. Anatomical redundancy 2. Morphological parahomology 2. DNA functional 3. Functional 2. Molecular redundancy 4. The strange past parahomology 3. Transposons 5. Stages of speciation 3. Anatomical 4. Redundant pseudogenes 6. Speciation events convergence 5. Endogenous retroviruses 7. Morphological rates 4. Molecular 8. Genetic rates convergence 5. Anatomical suboptimal function Closing remarks 6. Molecular suboptimal function What is Universal Common Descent? niversal common descent is the hypothesis that all living, terrestrial organisms are genealogically related. All existing species originated gradually by biological, reproductive processes on a geological timescale. Modern organisms are the genetic descendants of one original species or communal gene pool. Genetical "gradualness", a much misunderstood term, is a mode of biological change that is dependent on population phenomena; it is not a statement about the rate or tempo of evolution. Truly genetically Other Links: A Critique of Douglas Theobald's "29 Evidences for Macroevolution" Lawyer, Churches of Christ minister, and young-earth creationist Ashby Camp argues that the evidence is insufficient to establish that all organisms share the same biological ancestor. Theobald Responds to Ashby Camp's "Critique" The author of this essay has written a response to Camp. Search this FAQ gradual events are changes within the range of biological variation expected between two consecutive generations. Morphological change may appear fast, geologically speaking, yet still be genetically gradual (Darwin 1872, pp. 312-317; Dawkins 1996, p.241; Gould 2002, pp. 150-152; Mayr 1991, pp. 42-47; Rhodes 1983). Though gradualness is not a mechanism of evolutionary change, it imposes severe constraints on possible macroevolutionary events. Likewise, the requirement of gradualness necessarily restricts the possible mechanisms of common descent and adaptation, briefly discussed below. Common Descent Can Be Tested Independently of Mechanistic Theories In this essay, universal common descent alone is specifically considered and weighed against the scientific evidence. In general, separate "microevolutionary" theories are left unaddressed. Microevolutionary theories are gradualistic explanatory mechanisms that biologists use to account for the origin and evolution of macroevolutionary adaptations and variation. These mechanisms include such concepts as natural selection, genetic drift, sexual selection, neutral evolution, and theories of speciation. The fundamentals of genetics, developmental biology, molecular biology, biochemistry, and geology are assumed to be fundamentally correct— especially those that do not directly purport to explain adaptation. However, whether microevolutionary theories are sufficient to account for macroevolutionary adaptations is a question that is left open. Therefore, the evidence for common descent discussed here is independent of specific gradualistic explanatory mechanisms. None of the dozens of predictions directly address how macroevolution has occurred, how fins were able to develop into limbs, how the leopard got its spots, or how the vertebrate eye evolved. None of the evidence recounted here assumes that natural selection is valid. None of the evidence assumes that natural selection is sufficient for generating adaptations or the differences between species and other taxa. Because of this evidentiary independence, the validity of the macroevolutionary conclusion does not depend on whether natural selection, or the inheritance of acquired characaters, or a force vitale, or something else is the true mechanism of adaptive evolutionary change. The scientific case for common descent stands, regardless. Furthermore, because it is not part of evolutionary theory, abiogenesis also is not considered in this discussion of macroevolution: abiogenesis is an independent hypothesis. In evolutionary theory it is taken as axiomatic that an original self-replicating life form existed in the distant past, regardless of its origin. All scientific theories have their respective, specific explanatory domains; no scientific theory proposes to explain everything. Quantum mechanics does not explain the ultimate origin of particles and energy, even though nothing in that theory could work without particles and energy. Neither Newton's theory of universal gravitation nor the general theory of relativity attempt to explain the origin of matter or gravity, even though both theories would be meaningless without the a priori existence of gravity and matter. Similarly, universal common descent is restricted to the biological patterns found in the Earth's biota; it does not attempt to explain the ultimate origin of life. What is Meant by "Scientific Evidence" for Common Descent? Scientific theories are validated by empirical testing against physical observations. Theories are not judged simply by their logical compatibility with the available data. Independent empirical testability is the hallmark of science—in science, an explanation must not only be compatible with the observed data, it must also be testable. By "testable" we mean that the hypothesis makes predictions about what observable evidence would be consistent and what would be incompatible with the hypothesis. Simple compatibility, in itself, is insufficient as scientific evidence, because all physical observations are consistent with an infinite number of unscientific conjectures. Furthermore, a scientific explanation must make risky predictions— the predictions should be necessary if the theory is correct, and few other theories should make the same necessary predictions. As a clear example of an untestable, unscientific, hypothesis that is perfectly consistent with empirical observations, consider