The word "evolution" in its most basic terms simply means "change over time". In biological terms, it is the inheritance of genetic traits within populations of organisms through successive generations. Evolution is one of the most strongly supported scientific theories and is in fact the cornerstone of modern biology.
How it works
Evolution has two main components. The first is descent with modification. An offspring is like its parent(s) but not exactly like its parent(s). The reason for this is the random changes that occur in the propagation of genes between generations. Parent DNA is copied faithfully, but not exactly to the child. Sometimes part of the code gets pasted in backward, sometimes a chunk moves from page 1003 to page 1209, sometimes a bit is left out or another bit tacked on. There are a number of ways for information to be added, subtracted, or simply changed in a gene sequence.
Whereas an error in a computer program will cause it to crash and stop running, organisms can be more flexible. Sometimes a mutation can be crippling or fatal, other times it is a superficial change, and on some occasions the change is beneficial. The vast majority are completely neutral, either occurring in non-coding DNA or not changing the performance of the gene in which it occurs. You yourself are the heritor of some 120 (average number for humans) changes and probably aren't particularly crippled or enhanced by them. A specific mutation will typically only occur once and then spread through the population. Some mutations spread by virtue of being beneficial while others spread completely by chance in a process known as genetic drift. It is through genetic drift and mathematical models that scientists can trace evolutionary paths and genetic mutations back through history, in a process similar to the study of how language mutates over time.
The second component of evolution is a selection process—stated succinctly, that which survives to reproduce becomes more widespread. This is often referred to as natural selection, but in principle, we see selection processes every day. Whether you use Firefox or Chrome or Internet Explorer is a complex process of artificial selection, for example, and there are many reasons why different browsers control their respective market shares. Like organisms, companies, charities, even whole political systems spawn, grow, and die. What makes the evolution of organisms "natural" is that it has to do with conditions of adaptability, fertility, and more—what determines an organism's ability to propagate itself are factors derived from nature. And in the most trivial case, an organism that can't reproduce in some way (whether it's true sexual or asexual reproduction or simply the mechanism of a virus forcing a host cell to make copies) dies off and, well, vanishes.
Major factors that drive speciation through selection are geographical or climatological in nature: when populations get separated by mountains or rivers, the split-off groups can diverge; when the local weather patterns turn rainier or warmer, creatures built for cold, dry weather die off. Additionally, a creature may have a competitive advantage for limited resources. Plants that grow higher than others get a clear, unobstructed path to sunlight. Animals that are faster, bigger, or tougher can more easily kill their prey, or those that are fast and quick can outrun predators that might hunt them, or those that are smaller and weaker require less food and so do not starve. Organisms that are more attractive to the opposite sex can have more offspring. There are too many factors to list, of course; this is just a sample of what all affects an organism's ability to reproduce, to survive selection and the passage of time. In the end, no matter the cause, that which survives to reproduce becomes more prevalent, whatever that may be. It's a misconception to think only the "fittest" survive; this is not true. There's an element of chance (anyone can get hit by a falling rock). Plus, a great number of organisms survive to have children; it's whether they have more surviving children and grandchildren that determines the course of change.
Some dates to keep in mind regarding the history of life on Earth, according to evolutionary biology:
- The Earth itself is around 4.6 billion years old.
- The first simple life (that is, prokaryotic and single cellular) appeared around 3.5 billion years ago.
- Photosynthetic bacteria have been dated at 3.4 billion years old.
- Multicellular life did not appear until around 1 billion years ago.
- Animals (everything from jellyfish to scorpions to elephants) might have only been around for 550 million years or so.
- Flowering plants didn't appear until around 130 million years ago.
- Our genus, Homo, is only about 2.5 million years old. That includes our earlier bipedal ancestors.
- "Modern" humans only really popped up around 200,000 years ago.
- Cro-Magnons (the first Homo sapiens) originated around 50,000 years ago.
Notably, a particularly virulent strain of conservative Christianity has had issues reconciling evolutionary biology with The Bible's creation account in Genesis. Some have decided to take Genesis as metaphorical and/or believe that God drove the evolutionary processnote . Others say that the two views are irreconcilable and side with the Biblical account; while they can't deny the selection process or genetic drift on a small scale, they believe it only goes as far as forming different breeds within a species, not entirely different species (the degree of variation that constitutes creationist "microevolution" is usually arbitrarily small, or simply left undefined to stop those meddlin' scientists having any testable predictions to investigate). This view of microevolution has no scientific basis, and is a bit akin to saying "I believe that I can walk to the convenience store down the street, but not that I can walk to the next town seven miles away." In truth, the same mechanisms Young Earth Creationists try to Hand Wave into their version of microevolution are what cause macroevolution (ie, the change of organisms via natural selection), just as the same mechanism by which our notional creationist gets to the shop a short distance away (i.e walking) can get him to the next town a longer way away. In fact, macroevolution is simply all the microevolution in a given species.
Scientific Disputes within Evolution
While all serious biologists agree that evolution is a real process, like any scientific field of study, there is still some quibbling over certain details, such as the speed at which it occurs (phyletic gradualism, or a slow accumulation of changes over time, vs. punctuated equilibrium, or periods of little or no noticeable change interrupted by periods of great change in a short amount of time, like what might be caused by mass extinction events or population bottlenecks). There also is some debate between the Darwinist school of thought which holds random mutations as the primary source of evolutionary innovation, and a relatively newer theory of Symbiogenesis which instead emphasizes associations with other organisms that provide novel traits as a result of symbiotic relationships during times of environmental stress.
This is compounded by the fact that evolution is a bit trickier to follow in bacteria since they have the ability to pass their genes to other bacteria they encounter through a process called "horizontal gene transfer", and so bacterial populations have the ability to gain new traits from processes other than random mutation. The most famous example of this is probably the acquisition of antibiotic resistance genes across bacterial strains. Because of this ability, some scientists go as far as to argue that you can't even classify bacteria strictly into separate species since the classical biological definition of a "species" can't be applied to them!
Because of this wackiness with single-celled prokaryotes, most of the larger misconceptions that are addressed on this page have to do with animals and plants, as they are the organisms that most people are more familiar with and understand the best.
Also, keep in mind, despite these certain differences and disagreements, it all still assumes the fundamental tenets of evolution, that all populations of organisms have variations in their genetic information (no matter whether they come from mutations or were picked up from other organisms), and that not all of them will be able to produce offspring to carry on that information in the population.
Linnaean taxonomy classifies organisms based on their morphological characteristics into a hierarchical system. For example, humans are in Domain Eukaryota, Kingdom Animalia, Phylum Chordata, Class Mammalia, Order Primates, Family Hominidae, Genus Homo and Species sapiens. Unfortunately, not everything fits into this neat arrangement, especially once common descent is taken into account.
The Linnaean Taxonomy has precedents stretching back to antiquity, organizing life by kind and in a kind of ladder. God above man above animals above plants. However the hierarchy breaks down in the face of history, as single-celled organisms are more numerous and diverse than multi-cellular organisms. They had three billion years plus to evolve, so this makes sense, but it flies in the face of the anthropocentric world-view that holds life in a hierarchy with ourselves at the top. Further, the divisions between groups break down when you consider, for example, the primitive ancestors of mammals with characteristics commonly seen in reptiles, or when you learn that the birds are closely related to and recently descended from reptiles, making them closer cousins to crocodiles than crocodiles are to turtles, even though both of the latter are clearly reptiles!
The solution is a difficult one, particularly as Phillip and his Soup are so pleasing to the memory and to the aesthetic sensibilities of schoolchildren, but biology is switching over to cladistics. A clade is any group of organisms descended from a species. So in plants you could have the clade that includes mosses, ferns, conifers, and flowering plants. Or you could move up, pick a different ancestor species, and define a subclade that excludes mosses (who split earlier from the other plants), but which includes ferns, conifers, and flowers.
In the same fashion, you have the clade Dinosauria, which includes birds and non-avian dinosaurs. Go back to an earlier ancestor and you have the Archosauria, which clade includes dinosaurs (including birds), pterosaurs and pseudosuchians (crocodiles and friends). Go back further and your clade becomes Diapsida, including Archosauria, Lepidosauria (lizards and snakes) and maybe Testudines (turtles, which were once though to be non-diapsid reptiles). At that point your clade includes all living reptiles and, under the Linnaean system, would have been considered Kingdom Animalia, Phylum Cordata, Class Reptilia. However, your clade also includes the birds, which under Linnaeus were sorted into the separate Class of Aves.
Cladistics means that our understanding of life is less tidy and hierarchical, but considerably more organic. The tree of life now has three main branches of Archaea, Bacteria, and Eukaryota. Eukaryota has a sub-clade of multi-cellular organisms, some of which developed the protein collagen, which includes a sub-clade of bilateral animals (which excludes jellyfish, but includes insects), with a sub-clade of vertebrates (which includes all the fish), with a sub-clade of tetrapods (we're up to land animals, now), some of which developed amnions to help birth along, some of which developed hair and mammary glands, some of which developed an upright, bipedal posture and started smoking cigarettes because smoking is cool.
The Linnaean system has been retrofitted and adapted to help continue to organize life, but the tree of life is many-branched, as can be seen in this chart of the human taxonomy, which lists fifty-six clades, beginning with biota (all life) and ending with our subspecies, sapiens sapiens. Cladistics allows us to clearly sort ourselves and our ancestors, some of whom were mammals, some of whom were not, and some of whom had many characteristics common to mammals and absent in non-mammals but which clearly were not mammals. Rather than invent subphyla and superphyla and legions and metalegions, it makes more sense to consider this a historical science rather than a categorical science, and do our best to understand what happened when.
An alternative terminology is "monophyletic", "paraphyletic", and polyphyletic. A monophyletic group is (by definition) a clade. A group of organisms which excludes one group descended from that group is paraphyletic. A polyphyletic group consists of unrelated organisms that just so happens to resemble each other. For example, "fish" is a paraphyletic group, because there exist organisms (e.g. all land vertebrates) which are descended from fish but are not fish. However "cat" is monophyletic (a clade) - all current cat species are descended from a single ancestral proto-cat, and all descendants of the proto-cat are in the group "cat". The obsolete order "Insectivora" is polyphyletic, since golden moles and tenrecs are not closely related to shrews, moles, and hedgehogs, but were included in that group for a while before being moved to their own clade. The classification of some groups is surprising - brown (grizzly) bears are paraphyletic (any clade including all brown bears also includes polar bears.)
Common Misconceptions about Evolution
As with any significant theory, many myths, lies, and other misunderstandings have become attached to evolution and natural selection over the years:
Myth: Evolution picks winners.
- It's actually the other way around: Evolution picks losers. Organisms which are ill-suited to their environments, and the genes that make them ill-suited, are selected against. In a sense, "winning" evolution would be having children who have children who have children ad infinitum. There are no winners in this Endless Game, just organisms that haven't lost yet.
Myth: Evolution is leading somewhere, or knows where it's going, and that place is human intelligence.
- Evolution is simply a combination of random change and environmental pressure. What happens is that poorly adapted individuals die or reproduce less, not that something will magically appear that is perfectly suited to the environment. Happening as it does over hundreds of generations, modification and selection only guarantees you the minimum necessary to survive to this moment, not the best of all possible worlds. So, while you might be best-adapted today, that doesn't mean you will be tomorrow when something new evolves—or shows up by some other method. Take for example extremely isolated islands; in the absence of small mammals, birds adapted to fit the various niches that rodents would have occupied, but were then lethally out-competed when rodents showed up on European ships.
- And no, humans are not specifically the target of evolution. Were you to rewind history a few million years and play it forward again, there is no guarantee that a species would emerge that was a) bipedal, b) as intelligent as we are today and/or c) derived from apes, all of which are significant components of Homo sapiens. Were humanity to disappear today, it's questionable as to whether another species would achieve high intelligence, much less the other two.
- There are two schools of thought in the field of biology. The first, represented by Richard Dawkins is that if you were to rewind history prior to the emergence of our hominid ancestors, you would see the rise of bipedal, intelligent apes. They wouldn't be precisely human; the details would be different, but the overall organism would be very similar. The other, represented by Stephen J Gould, is that evolution is essentially stochastic (non-deterministic) and our hominid ancestors could easily go in another direction and intelligence might never appear.
- Research has actually been done on this point, and it turns out that both schools make valid points. The research was to follow populations of E. Coli for tens or hundreds of thousands of generations under varying conditions (which, given their life cycles, only takes a few weeks/months) and observe the result. Under tightly controlled conditions, the first school of thought holds; the result is the same overall, with varying details. Where conditions are more variable, the results are more variable and the second school of thought holds. Thus the argument has morphed to "Is the environment on Earth such that intelligence is an inevitable result or is intelligence a product of random exploration of the landscape of possible forms?" Until and unless we get the opportunity to observe alien biological histories, or the independent rise of intelligence multiple times on Earth, we may never know.
- There are not "more evolved" (mammals and birds) and "less evolved" (reptiles, amphibians, fish, invertebrates, non-animal organisms) species. All living things are descended from a common ancestor, and have the same three or so billion years of evolution between then and now. (While species aren't more or less evolved, they can be more or less complex. Lineages can evolve from high to low complexity - think of lizards losing legs to become snakes.) If you really pressed an evolutionary biologist to pick "more evolved" organisms, they'd reason that natural selection is most effective with short generation times and large populations, and therefore choose bacteria.
Myth: Evolution is nothing but chance.
- One of the arguments thrown at evolution is that "none of this could have just happened by chance" (see above re: religion). No evolutionary biologist argues that this is the case. Chance is flipping a million coins and having them all land on heads. Evolution by descent with modification and natural selection is flipping a million coins, keeping the heads, flipping the rest, keeping the heads, flipping the rest... If you think about it, the whole point of evolution is to accumulate "luck" in this way.
Myth: Evolution churns out perfection.
- Evolution gives us organisms that are able to survive in their environments, not organisms that are best at surviving in their environments. Remember what was stated above: evolution doesn't pick winners, it selects against "losers", or those that aren't able to produce offspring. As long as you're able to pass on your genetic information, whatever traits and adaptations you have will be kept in the gene pool, even if they aren't the most ideal traits for organisms to have. Some organisms may have certain traits not because they give any sort of appreciable benefit at all, but just because that's the trait that happened to be dominant through genetic drift or other random occurrences.
Remember, evolution is not guided with any sort of specific end or goal in mind, and it is only focused on the ability of the organism to produce offspring. So negative traits that only show up AFTER the individual has reproduced are not selected against. This is why some degenerative conditions like Huntington's disease are still present in human populations, whereas other genetic disorders are selected against because they eliminate bearers before those bearers reach reproductive maturity.
Myth: Evolution is about the origin of life.
- Evolution tells us how life changes once it's already here, not how it formed in the first place. The latter is known as abiogenesis and is the realm of biochemists and organic chemists. Not evolutionary biologists.
- And not having the answer to this question doesn't invalidate natural selection or common descent anymore than gravity and thermodynamics are invalidated by physics not having the answer to how matter and energy came into existence (also known as the first cause argument and/or complexity of the universe argument). To put it another way, not knowing who your father is doesn't mean you didn't have one.
- That said, the study of abiogenesis is a vibrant field. Scientists have long known that vitalism (the hypothesis that life involves a "vital element" that can't be replicated with "mere chemicals") is untrue, at least for purposes of the science of biology. And numerous experiments have suggested that early-earth conditions would naturally give rise to basic organic molecules, albeit with some serious difficulties that need to be worked out. The current consensus, drawn from a variety of evidence (genome comparisons and direct observations of certain environments) is that the last universal common ancestor arose in heat vents at the bottom of the ocean, where there is still life today. Unfortunately, the process is almost certainly non-repeatable outside of a very well-controlled lab, because any naturally-forming organic molecules will get gobbled up by existing life before they have to chance to "become alive."
Myth: Evolution is about the origin of the Earth/the origin of the universe.
- While astronomers do use terms like "cosmic evolution" when discussing the history of the universe, or "stellar evolution" when discussing how a star changes over its lifetime, these terms have nothing to do with what biologists mean when they say "evolution." Biologists always mean biological evolution, and in any discussion of "evolution" all parties involved should assume that they're talking about biological evolution unless another, specific meaning of evolution is presented as the topic up front.
Myth: If people evolved from monkeys, there should not be monkeys.
There are two incorrect assumptions present in this (annoyingly persistent) question. The first incorrect assumption is simple to correct, but the second is more pernicious.
- The first incorrect assumption is a somewhat pedantic one: modern humans did not evolve from modern monkeys, or at least from ancestors that would be fully classed as monkeys; in fact, both humans and monkeys evolved from some common antecedent that predated the emergence of the first monkeys. It would be more correct to ask "If people evolved from apes...", except that we're still apes. One of our closest relative is the bonobo, which may explain a lot.
- The second incorrect assumption is that evolution is a ladder of progress, and that an entire species must evolve into a different species that supplants the original species, leaving no members of it behind. Evolution, in fact, is not a ladder so much as a branching tree of contingency. Speciation usually occurs when a small group from a much larger population is reproductively isolated from the rest of that population, most often through geographic isolation. This smaller population continues to breed amongst themselves, and will generally be operating under different selection pressures than the population they came from. Eventually, so many genetic differences will accrue that the members of this new population can no longer interbreed with the other population, and it's at this point that we say a new species has arisen. We started with one species, and ended up with two species, and the second one is good at thriving in its new, different, environment.
This same mechanism happened with our ancient ancestors: We started with one large population pool in Africa that was pretty much chimp-like, then about 4-6 million years ago some of those chimp-like ancestors got separated from the rest of them and began exploiting a slightly different biological niche in a different part of Africa, until they'd diverged far enough from their ancestors that they could no longer interbreed with the rest of the chimp-like creatures. Meanwhile, because those original chimp-like creatures were now isolated from us, they went on to become modern chimps.
In short, the question is a little like claiming that airplanes should have obsoleted cars. True, the two objects share a purpose — getting human beings from Here to There — but have different operating requirements and thrive under different conditions. Airplanes should not have replaced cars because airplanes are not good at doing what cars are good at doing, and vice versa.
Myth: The theory of natural selection is a tautology.
This is usually phrased thusly: Natural selection is all about survival of the fittest, but fitness is determined by what survives, and 'round we go. Thus it has no real informational content; it doesn't describe the world any more than the statement that all chairs are chairs.
- In fact, fitness is defined as the average contribution by a particular organism/genotype/phenotype to the gene pool of the succeeding generation. This isn't the nebulous "survival" (recall that no one survives in the long run), but is in fact a mathematical definition that allows the comparison of genes, gene-plexes, organisms, populations, etc.
- Further, evolution doesn't occur in a vacuum; we observe it within a functional ecology and can make predictions about which genes will survive and propagate. The classic example would be the moths of England. In the absence of soot-producing coal fires, black moths were selected against because they were highly visible against tree bark; once England industrialized and the background was darkened with soot, the rate of success changed. Presented with the two kinds of moths and the information that soot is darkening the countryside, a prediction about the relative fitness is easy and inevitable. note
- Finally, in studying fitness, we have to recognize that two genotypes may have absolutely no competitive edge over one another. Neither is more fit, and how each fares will be the result of genetic drift, or allelic drift, in which the survival of each will be the result of random chance rather than natural selection. One might disappear, or both might continue. In the absence of an actual definition of fitness (as proposed by the myth), genetic drift and an absence of fitness would be incoherent concepts, which they are not.
Myth: Evolution predicts chimeras.
Behold, the mighty Crocoduck! This myth states that the transitional forms of species are the melding of two existing species. That is to say, something that is half cat, half dog. A mermaid, a hippogriff, a chimera.
- In fact, a transitional form is a form intermediate between a currently living form and its ancestor. For example, Darwin himself reasoned that birds are descended from a family of ancient reptilians, and predicted that there should therefore be a transitional form sharing characteristics common to both birds and reptiles. Just two years after the publication of Origins, Archaeopteryx was discovered with a snout containing teeth, feathers on half-formed wings, wingbones not fully fused, and other qualities placing it intermediate between the two forms. This remarkable predictive power is why evolution is today the fundamental theory of biology.
- A related misconception is about common ancestry. Bears, dogs, and cats (all members of the order Carnivora) are related, and bears and dogs are more closely related to each other than either is to cats (bears and dogs are both members of the suborder caniformia, while cats are members of feliformia). Thus you go back a certain amount of time and you find the common ancestor to both the bear and the dog. It is not a beardog. Rather, it shares characteristics common to both (hair, carnivorous diet), some that are unique to either (the ancestor walked flat on its feet [plantigrade, like us] whereas the dog family walks on its toes [digitigrade]), and some that are found in neither. The ancestor looked more like a badger (it wasn't one) than like either bears or dogs, but had a wider, more bearlike head; a snout longer than a bear's and shorter than a dog's; and it was about the size of a raccoon. You would have to go back even further to find the common ancestor of dogs, cats, and bears, and you'll find that it's not a fusion of the three modern forms. Instead it is a less well-defined, creature, with broader characteristics and without the specific adaptations any of them have today. What it did have was traits suited to its time and place that had the potential to turn into what those creatures became.
- Want something that'll blow your mind? The closest living relatives of the bears today are the raccoons, skunks, weasels and pinnipeds; the seals, walruses, and sea lions. The hyena isn't a caniform at all! They're descended from a civet-like creature, making them feliforms more closely related to the mongoose! This is an example of convergent evolution and explains why biology is such a difficult and complex science; also, why you shouldn't judge a book by its cover and the power of genetic studies.
- Look! Transitional forms!
- In traditional Darwinian evolution, animal populations evolve by having genes either removed or added to the gene pool (more technically, the genetic frequencies change; for example the gene variant for red hair may go from being in 15% of the population to being in 3% in a few generations if it's become an easy target for predators, or a new gene variant that's extremely useful and has just appeared will go from being in 0% percent of the population to being in 80%); the offspring are the evolved form, not the parent, and even so it's rarely a huge change. These genes are present in the fertilized egg, and an organism becomes what it is through a process of embryonic development, and can't change much after that. Genetic changes in the cells of an organism only affect that cell, and are much more likely to lead to cancer than to anything useful. The only exception are bacteria and other simple lifeforms, which really can be modified by taking up new genes.
- This is an especially pernicious and harmful myth, as it was proposed by some "scientific" racists during the 19th century that non-white peoples were an example of "regressed" or "primordial" human, and thus inferior.
- Much evolution-themed fiction involves a Mad Scientist or a Negative Space Wedgie can hitting humans with rays that turns them into Neanderthals or modern monkeys. This would not really work. Your DNA is partial copy of your mother's DNA and your father's DNA, with several dozen mutations. Your body doesn't have all of the DNA necessary to make a perfect copy of either of your parents, let alone any distant ancestors.
- Besides, humans evolved from neither monkeys nor Neanderthals. Even if our genes did contain our "ancestral memory," it would take us to a genus of apes that weren't like any living apes; hitting a chimp with the "devolution ray" would also bring them back to that. And Neanderthals are likewise a cousin species of ours (possibly Kissing Cousins), not an ancestor species.
- That said, evolution can "reverse" course in a different way. There is a thing called "atavistic traits", or traits that were once found in ancestral species, and the genes that code for them are still present in the organism's genome, just not being expressed at the time. Occasionally a mutation will cause these atavistic traits to reappear. For example dolphins and pythons are sometimes born with little stumps of hind legs attached to their hip bones! However, the further back in time that these traits stopped being expressed, the more they get scrambled due to random mutations, and the less likely they are to reappear.
Myth: Speciation necessarily results in a "new" and "old" species, with the "old" one freezing as it was or instantly dying out.
- This is the source of the "if we came from chimps, why are there still chimps?" argument, and tends to assume that the "goal" of evolution is to become a bipedal tool-user with curious ideas about how it got there, so doing anything else isn't evolving. Even modern bacteria are vastly more sophisticated than their ancestors; they've spent the same amount of time getting better at being bacteria as any other species has spent getting better at being not-bacteria.
- What you get instead is where once there was a single population of a single species, you now have two populations that can no longer interbreed. Those two species may both be entirely different from what came before, or they may both be superficially similar but have significant internal or behavioral differences, or one could have stayed roughly the same while the other changed a great deal.
Myth: Evolution violates the Second Law of Thermodynamics.
This is a common misrepresentation of entropy, which is often simplified into "order eventually degrades into disorder." Thus, the following question is often asked of evolution: “If the Second Law of Thermodynamics states that entropy increases over time in a system, how is evolution, which goes from disorder to order, even possible?”
- Firstly, the law actually states that entropy, a measure of randomness, cannot decrease in an isolated system—i.e., things in an isolated system tend to even out: hotter areas lose heat to cooler areas, friction takes energy from motion, and so on until the system achieves equilibrium. Hence, why there is no such thing as perpetual motion. However, biological processes take place in our planet, which is not an isolated system. Earth's biosphere receives energy and material from the Sun, other space debris and phenomena, and geothermal activity; so applying this law to evolution as a whole is based on a faulty premise.
- Secondly, if the Earth's biosphere actually was a closed system, then it is true that evolution would not happen—but neither would life in the first place. Life is just the distribution of energy from one lifeform to another in the form of several processes of conversion (photosynthesis, digestion, decomposition etc.), and that process would need a constant supply of energy or it would peter down to equilibrium instead of encouraging growth. The lowest rungs of most food (energy) chains usually begin with something requiring photosynthesis, which takes energy from an outside source (the Sun) and/or geothermal energy (exclusively the latter for life thriving in places with no sunlight).
- Lastly, evolution does not go from "disorder to order," which is basically another way of stating the Evolutionary Levels myth already discussed in previous sections.
Myth: Humans are no longer evolving.
Yes we are.
- People don't like to think that we're subject to the same impersonal forces of evolution, that things are going on in our brains that we don't understand, and that we're making choices we're not choosing to make. The funny thing is, we're all repulsed by the smell of rotting meat; some of us perhaps moreso than others. Perhaps some of us are more sensitive to that and thus make dietary choices that give them an advantage, which can be passed on. Perhaps some of us are better able to tolerate food that's less fresh, which is also an advantage that could be passed on, and which means that being repulsed by unfresh food would no longer confer an advantage! Are either of those traits better? Only time would truly tell.
- In any event, people aren't fully cognizant of all the processes going on in either body or mind, and their choices aren't fully rational (though if you ask them about it, you'll probably get an excellent post hoc rationalization attempting to justify it). Humans are subject to environmental and population pressures, and those are going to confer advantages on some people and not on others. Because we can't fully explicate what those pressures are, and are almost completely unable to predict what they'll be in a thousand years time, it's almost impossible to predict what humans will evolve to become, but that doesn't mean we aren't evolving.
- Similarly, we can control the path somewhat. For example, Adolf Hitler made a darn good stab at eliminating Semitic traits from the European population, and modern medicine has made it unnecessary to be resistant to either small pox or the black plague. However, that doesn't mean we can control all things nor even that we should.
Myth: All human traits evolved in the stone age.
Related to the above; people are squeamish about the idea that humans are still subject to natural selection. Thus they conclude that perhaps we used to evolve, but don't any longer.
- This is one of the central tenets of Evolutionary Psychology, a field awash with, if not completely dominated by, pseudoscience. They take a common trait (eg. girls prefer pink and boys prefer blue note .), assume it's a universal trait, and then find a post hoc rationalization (eg. boys were hunters, girls were gatherers that needed to be able to see berries). The field is mostly false because 1) those traits usually aren't universal (girls don't universally prefer pink and boys don't universally prefer blue), 2) there's no reason to suppose such a thing evolved rather than being a cultural issue (in China, everyone prefers pink because it's a shade of red and red is lucky, whereas in some places red is unlucky and associated with death because of blood), and 3) there's no way to test their random rationalizations. That's not to say that perhaps Evo Psych couldn't someday be a field worth studying, but right now it's a haven of racism, and misogyny.
- Evolutionary Psychology has a deservedly bad reputation for publishing ludicrous studies like the above, but also for there absurdly broad conclusions (women all behave X when they're ovulating, for example), despite the evidence from their own study explicitly contradicting that conclusion. (Conclusion: Women would walk more sexfully when they were ovulating, but they're all lying so men don't know they're ovulating. Also, men do find women more attractive when they're ovulating, but they're all lying to themselves so that they'll remain faithful.)
- Yes, psychology is based in biology, and yes, many behaviors are going to have concrete advantages that are separate from shifting and non-genetic culture, but evolutionary psychology as it currently stands doesn't make any sort of distinction like that, with its most popular journals publishing papers that simply assert a behavior is both universal and genetically determined, then telling a Just So story about how that behavior was set in stone back in the Stone Age.
- This is all false because, as above:
- Humans are still evolving, so, no, not all traits came from the stone age. Some came from after the stone age.
- Humans carry traits from well before the stone age. Our tetrapodal pentadactyl status (four limbs, five digits) evolved well before the stone age.
- Behaviors, unlike basic physiology, are highly plastic (as with the pink/blue boy/girl example) and don't have to have a genetic basis. Some behaviors can (eating, pooping), others probably not so much (liking the Jonas brothers, wearing your pants around your hips rather than your waist).
- Behaviors, unlike physiology or tools, aren't easily preserved by burial or fossilization, so it can be very difficult to say how people behaved in the stone age
- Finally, stone age humans lived in all habitats and explored all lifestyles (hunting, gathering, pre-farming, farming, fishing, practicing warfare, being uber-peaceful hippies...), so gross generalizations about jungle-dwelling hunter-gatherers really can't be applied to whale-hunting Inuit or Mesopotamian farmers.
Myth: All human traits were chosen by natural selection.
Megan: That's just the kind of sexism that discredits evo-psych! Your "evolutionary histories" always seem tuned to produce 1950s gender roles!
Cueball: Evolutionary wha—? I meant Savannah, Georgia.
Megan: Hey! Leave my mom out of this!
And thus they are awesome and everything has a purpose and trying to change anything is bad!
- First, recall that evolution doesn't lead to the best of all possible worlds, just the minimum necessary to get where we are now.
- Just because a trait evolved doesn't make it good.
- Some traits are evolutionary hangovers that we're still working to get rid of, like the vermiform appendix.
- Some traits are kludged together and okay at the moment, but hopefully they'll get better, like our rather wonky lower backs and prostates and pelvises.
- Some traits are just plain bad, but still occur in a sizable portion of the population, like breast cancer.
- Some traits were selected for in an ancestral environment that doesn't entirely apply today. For example, it's likely that we react positively to sweet and fatty tastes because those would always correspond to healthy fruits and rare meats; today, we can replicate the essence of those things with a "superstimulus" we call junk food.
- Not all traits are chosen by selection; recall that a significant portion of evolution is just randomness. Think of genetic drift (pure chance selecting for traits that are neither good nor bad, like hair color) or genetic draft (a bad or neutral gene [eg male pattern baldness] being very close to a good gene [eg being Wolverine or Batman]).
- In fact, there are mathematical models that demonstrate the prominence of either selection pressures or random factors in a population. Essentially, the larger a population, the more of a role selection has in the situation (though chance still plays a part). A small population is dominated by chance (though of course selection is still present).
- So which is humanity? Large or small? You might think that seven billion people (7e9, 7x10^9) is a large population, but no; that's how many bacteria you can fit in a test tube. Humanity is a small population mostly dominated by chance. Selection has played a role in our history, but chance has played a larger one. Selection plays a role in large populations like that of pelagibacter, an oceanic bacterium with roughly 2x10^28 individuals (or 3x10^18 times that of humanity, or 3 sextillion times as many).
- This ties back into the earlier myth, that evolution knows where it's going and human intelligence is the goal. Given the large role of chance in our history... probably not.
- Claiming evolution isn't a scientific theory would be like trying to claim that plate tectonics isn't a scientific theory. Just because a large portion of the research is in the form of forensic field work digging up clues millions or billions of years old doesn't mean it's not a science. Biology, geology, and even astronomy also have their theoretical researchers, their lab-work, and their strong ties to chemistry and physics (that more neatly conform to the popular view of scientific work). Just because the work is hard and doesn't take place on a lab bench doesn't mean it's not science.
- To build a theory, you must gather a great deal of evidence (which biologists have done. Literally, tons of evidence. Enough fossils to fill museums. Again, literally. They're frickin' huge rocks.). This evidence, these millions of individual facts, allow you to notice trends, which are cataloged as laws. These many laws are brought together and put into an over-arching framework. This framework brings together all the evidence, all the laws, and explains them. This framework is a theory. A theory is the final goal of scientific research and is incredibly difficult to build because it requires millions of facts, millions of man-hours to put together, and a single irrefutable fact can bring it crashing down. The theory of evolution explains centuries of careful work by biologists and in the more than 150 years since it was put forward by Darwin, it hasn't been pulled apart. It is a scientific theory, and one of the best and strongest we have.
- In a similar way, history is also a science. It pulls together the difficult and laborious fields of linguistics, archaeology, anthropology, physical anthropology, psychology, and the half-dozen or so fields concerned with understanding historical texts in order to build theories not only of what happened when, but why.
Myth: Evolution is just a theory
- This is when people mistake the popular definition of "theory" with the scientific definition. A scientific theory is an explanation for a portion of the natural world supported by a large amount of evidence, which can then be used to make predictions about how the natural world will behave. Most people use the term "theory" in the way that scientists would use "hypothesis": a proposed explanation for some phenomena.
- Attempts to claim that evolution is just a theory tend to ignore other scientific theories such as plate tectonics, germ theory, atomic theory, and the theory of gravity. While there are some fringe pseudoscientists who take issue with these individually, most people don't make the realization that if evolution is questionable because it is "just a theory" then so is gravity. Amusingly, gravity is less well understood than evolution, but much more widely accepted.
- The idea that evolution implies a cut throat social world is false for a few different reasons.
- Evolution is a descriptive theory about how species operate and not a prescriptive theory about human ethics - that is, it's about how nature is, not how society should be.
- It's impossible to know what future selection pressures will befall any organism so maintaining genetic biodiversity is important.
- Evolutionary arms races can lead to adaptations that, through cost of having it outweighing the benefits it provides, will cause one or both species to go extinct; if a predator causes its food source to go extinct, it will go extinct too.
- Evolution can lead to cooperation as the ability to get along well with others and work in teams can contribute to an organisms fitness.
- Finally as stated above the products of evolution aren't really all they're cracked up to be.
- Specific phenomena cited as mechanisms organisms can use to overcome nature's every organism for themselves free for all include kin selection, reciprocal altruism, and memetics.
- Kin Selection centers around the idea that genes are what's selected for instead of organisms. A gene competes not only with the genes in other organisms but also the other genes in the organism it is a part of. Most genes aren't present in a single organism though and are present across multiple organisms so it makes sense for the same genes in different organisms to cooperate with each other to increase their presence in the next generation.
- Reciprocal altruism is where one organism helps out another organism in exchange for help from that organism in the future. For instance if a monkey wasn't able to find food that day but other monkeys in the group found more than they need. The monkey with an excess can give some to the monkey who doesn't have any in the hopes that the monkey without any food will return the favor in the future when the monkey with an excess needs help. This can be seen as taking out an insurance policy for when times get rough.
- Added on to this idea is the idea of competitive altruism. Where organisms have to find the right balance between being cooperative and beinng choosy. If they are too cooperative then they can easily get taken advantage of. If they are too choosy then they won't be trusted because they barely help out.
- Memetics is the theory that ideas(or memes) are alive just like organisms. While bacteria reproduce through dividing and many animals reproduce through sex ideas reproduce by getting their host to use language to implant them into another hosts brain. In theory they can do this even at the cost of genetic fitness to the host organism. For instance the Shakers of the 1800's were able to survive for a while despite one of their doctrines being that adherents can't ever reproduce. They did this by taking in the many orphans and widows of Victorian society.