Why do atheists believe in macro-evolution? It is so contradictory it is hilarious.

The topic of the debate suggests that Con wants to debate the resolution that macroevolution "is so contradictory it is hilarious." However, he has chosen the "Con" position, and it does not seem that he opposes that statement. Nor can I find any resolution in the opening statement which Con might argue against. I will therefore assume that Con is contesting the truth of macroevolution. I will also assume that, as instigator who has not stipulated otherwise, he assumes the burden of proof to disprove evolution.Macroevolution is defined as evolutionary change at or above the species level.[1] The only argument Con makes that macroevolution is false is the argument that a single cell cannot become a complex multi-cellular organism. However, this argument is self-refuting; by making it, Con has shown that he exists, and therefore that he, as is the case with all humans, developed from a single-celled organism to a complex multi-cellular organism with functioning organs and organized cortical brain activity in only five or six months (and journeyed down a birth canal a few months after that). Thus, it is clearly possible for multi-cellular life to develop from single-cellular life.Since this is the only argument offered by Con, he has failed to make a prima facie case against macroevolution. However, having quite a few characters to spare, I will make a brief case of my own.Perhaps the most common-sensical argument for macroevolution is this: We know for a fact that microevolution (change below the species level) exists. We know for a fact that time exists. But that's all that macroevolution is: microevolution plus time. Given a sufficiently large accumulation of microevolutionary changes, a population of a given species will invariably reach the point where it can no longer interbreed with the original species. That by definition is speciation, which in turn by definition is macroevolution.The creationist can counter this argument in two ways. First, he can claim that there is some mechanistic barrier that prevents evolutionary change at the species level, while allowing it below that level. However, despite having much time and incentive to do so, they have never identified such a barrier.Second, he can claim that not enough time has elapsed in the history of the Earth for microevolution to lead to speciation, because the Earth is only, say, six thousand years old. However, radiometric dating has shown that the Earth is approximately 4.6 billion years old[2]; that is more than enough time for speciation to not only occur, but to occur so many times that all the diverse forms of life on Earth could have descended from a common ancestor -- and the evidence suggests that that is the case.Here are just a few more evidences for macroevolution.(1) All living organisms have inherited the same structures which perform the functions necessary for life, namely replication, heritability, catalysis and metabolism. Out of hundreds of naturally occurring amino acids, all protein molecules are built from the same set of 22. Out of hundreds of naturally occurring polymers, all life uses only three. If evolution were false, we might expect to find a life form on Earth that does not use polynucleotides, polypeptides or polysaccharides, or that does not use DNA, or that uses DNA without nucleic acids.[3]2) All species fall into nested hierarchies. That is all species can be classified objectively and in a manner that all biologists can agree upon. Anyone who learned the phrase "kings play chess on funny green squares" in school will know that this is the case. If evolution were false, we would expect to see species that could not be easily classified into such groupings, such as a tree with mammary glands, or the fabled "crocoduck." We don't.[4]3) Vestiges exist. Since a given feature of a species doesn't necessarily disappear when another species evolves from it due to the graduality of the process, we observe that there are vestiges -- anatomical or molecular structures that serve little or no purpose, but would serve a great purpose in another, perhaps closely related species. Examples of vestiges include ostrich wings, python pelvises, and the human coccyx, which is basically a skeletal structure that serves as the base of a tail. If evolution were false, then we should never find vestiges.[5]4) The geographical distribution of species are consistent with their genealogical relationships, since the Earth is dynamic and evolution occurs in space as well as time. For example, all marsupials on the Earth are native to Australia, or to regions that we know were once connected to Australia (and have since separated via continental drift). All alligators on Earth are native to eastern North America and eastern Asia, which again were once connected geologically. If evolution were false, we would expect to see a more profound scattering of life -- cacti growing natively in Australia, for instance, or lions roaming the North American plains. We don't.[6] Biologist Jerry Coyne noted in 2009 that "[t]he biogeographic evidence for evolution is now so powerful that I have never seen a creationist book, article, or lecture that has tried to refute it. Creationists simply pretend that the evidence doesn’t exist."[7]5) Transitional forms appear in the fossil record. Given the rare circumstances under which it is possible for an organism to fossilize, we do not have fossils of many or even most species which ever lived; nonetheless, the record that we do have is entirely consistent with the phylogenetic tree. One of the most famous examples is Archaeopteryx, a species that lived millions of years ago and fits on the phylogenetic tree at the point where reptiles and birds would share a common ancestor.[8]I could go on at great length, but hopefully this suffices to show that the evidence for macroevolution is plentiful and compelling; so much so that, given awareness of the evidence, a "blind leap of faith" is precisely what is needed to deny it.[1] Wilkins, J. "Macroevolution: Its Definition, Philosophy and History," available at http://www.talkorigins.org... updated 2006.[2] Dalrymple, B.G. The Age of the Earth (Stanford, 1991).[3] Theobald, D. "29+ Evidences for Macroevolution," available at http://www.talkorigins.org... last updated 2012; part 1.1.[4] Ibid., part 1.2.[5] Ibid., part 2.1.[6] Ibid., part 2.5.[7] Why Evolution Is True (Viking, 2009), p. 89.[8] Theobald (2012), part 1.4