Evolution Final
Compare the various models for the origin of Homo sapiens. How do the "Out-of-Africa," "Multiregional," and "Hybridization/Assimilation" models compare? What features / predictions do they share? Where do they differ?
"Out-of-Africa": H. erectus spread globally, Other Homo species derive from H. erectus., H. sapiens evolved in Africa, dispersed, displaced others, No interbreeding. "Multiregional": H. erectus spread globally, but maintained continuity as a single species, H. sapiens evolved via anagenic change within each region concurrently with gene flow to maintain single species. To think about how this differs from the Replacement model, imagine being able to sample ancient populations, and compare them with modern human populations. In this case we would see a big mixture. Present-day gene pools would be a mixture of the local populations and ancestral archaic populations. "Hybridization/Assimilation": somewhere in b/w the two; H. sapiens originated in Africa, migrated out, and replaced archaic species through interbreeding/assimilation. Limited evidence of competition, innovation, dramatic morphological change, though many disagree here. Most studies have supported African replacement model, with minor hybridization (Neanderthals, others?)
What's an ape? A great ape? African great ape? Where do humans fall within here? How does this relate to hominoids, hominids, hominins?
Ape: Hominoid; Gibbons, Orangutans, Gorilla, Chimps, & Humans; synapomorphies that help define them: Rel. large brains & more erect posture, No tail (reduced caudal vertebrae), Molars with five cusps, Greater flexibility of hips, ankles, wrist & thumb. Great apes: Hominid; Orangutans, Gorilla, Chimps, & Humans. African Great ape: Hominins; Gorilla, Chimps, & Humans, monophyletic, Elongated skull w/ enlarged brow ridge, Shortened, stout canine teeth, Fusion of certain wrist bones, Enlarged ovaries & mammary glands, Reduced hairiness. We are in the same family as chimps and gorillas, and substantial research shows chimps and humans to be sister hominins (with the chimp/human ancestor being sister to the gorillas).
The species we studied include Australopithecus afarensis ("Lucy"), Australopithecus sediba, Ardipithecus ramidus, Homo habilis, Homo erectus / ergaster, Homo floresiensis, H. heidelbergensis, H. neanderthalensis, Homo sapiens. If given a genus and/or species, where does it fall in the broad scheme, or relative to each other? Be sure you're familiar with some key details of each species, approximate time frame when each occurred, key anatomical features highlighted, relationship to other species (bigger brain? tool user? bipedal?).
Ardipithecus ramidus (4.4mya): Small head and brain (300-350 cc), Bipedal, but flat-footed w/ opposable toe, Long limbs w/ more flexible hands, Lived in mixed forest and grassland, May have been partially arboreal. Australopithecus afarensis "Lucy" (3-3.6 mya). Australopithecus sediba (2mya): represented what some believed a transition from Australopithecus to more derived Homo species. It dated to approximately 2 mya, which made it more recent than any other Australopithecus species. It also showed a mosaic of ancestral and derived features. Remember our discussion of whales and transitional fossils. A common misconception associated with a linear, progressive view of evolution is that transitional fossils should be intermediate in features. The reality is what some call mosaic evolution, which means that so-called "transitional fossils" should show a mix of ancestral, derived, and even novel traits. Just the hand of Australipithecus sediba showed that, with features more like their Australopithecus relatives, others more like later Homo species, and some, like the length of the thumb, that were entirely unique, What we know of Australopithecus sediba came from two individuals discovered in 2008 that seem to have fallen in a sinkhole. Their features are "so weird" according to one researcher, as they represent a mix, or mosaic, of ancestral and derived features. If you would give a specialist one part of the skeleton, they'd swear they were holding a chimpanzee bones. Give them another, they'd swear it was Australopithecus. Yet another and they'd swear it was Homo, perhaps even human. H. habilis (1.5-2.5mya), H. erectus/ergaster (0.5-1.9mya), H. floresiensis (17,000 yrs ago): ~ 3.5 ft tall & 50 lbs, Chimp / Lucy-sized brain, made stone tools, very recent (~17,000 yrs ago), Distinct hominid? Modern Homo with abnormality? Fraud?. H. heidelbergensis (200k-600k yrs ago): Large brain (1100-1400 cc), taller (males 5'9"), Intergraded b/w H. erectus and H. neanderthalensis, 30 individuals in inaccessible pit, one w/ hand axe of pink quartz, Suggests complex thought, symbolism, beliefs, etc., Relationship to other Homo uncertain, H. neanderthalensis (200k-300k yrs ago): Short, heavy-set, larger brains (1500 cc), Tough, committed hunters w/ primitive tools, Grew up quickly, smaller parietal & temporal lobe, similar frontal lobes to H. sapiens, Enormous energy demands (5,000 kC), Last trace, 28K near Rock of Gibraltar. H. sapiens (200k yrs ago): slightly heavier brow ridges, faces a little bigger, simple technology, Making similar tools as neanderthals.
Natural selection is the only process that results in evolution Related: Any misunderstanding that equates natural selection with evolution.
As we have seen with the start of this chapter, there are in fact five processes that affect evolution, which we now know to be a change in allele frequencies. Those mechanisms are natural selection, genetic drift, genetic mutation, migration, and non-random mating (recall however, that non-random mating alters genotypic frequencies, by itself, it does not alter allele frequencies). Natural selection is certainly the most powerful and pervasive of these mechanisms, in terms of contributing to evolutionary change, but by no means is it the only mechanism.
The fittest organisms are those that are strongest, fastest, healthiest, and/or largest.
As you've seen, "fitness" has a very different meaning in evolutionary biology. Fitness does not always indicate health. Fitness is the ability to get genes into the next generation relative to other individuals present and the current environment. Fitness doesn't always correlate with strength, speed, or size. A puny male bird with bright tail feathers might leave behind more offspring than a stronger, duller male, for example. Fitness of the scale-eating cichlid depended on how frequent your phenotype was. Fitness in the Florida panther certainly did not indicate health or vigor.
First, be sure you understand the broad relationships and biology of the major groups. Australopithecines (both gracile and robust). What about archaic Homo species vs. more modern Homo species?
Australopithecines "Archaic humans": Incl. famous "Lucy" (A. afarensis) and "Laetoli footprints", Many ancestral, intermediate features, Rel. large teeth and bipedal, Never been found with tools, Social, mostly vegetarian, strong prognathism (but slightly less than chimps), brain case (~400-500 cc; chimps ~ 350 cc; H. sapiens 1,200-1,400), curved finger and toe bones (sim. to chimps), Intermediate limb length (rel. to chimps and humans). Gracile older (2.5-4.5 mya) vs. Robust (1.0-2.4 mya) Robust: Larger "dish" face, jaws, molars, premolars, & chewing muscles (Note cranial ridge & zygomatic arch: Experts speculate that they may have been the more vegetarian of the two and fed upon tough plant material, such tubers, tough fruits and fibers. Both similar in height and brain size and walked upright. Went extinct. Archaic Homo species are H. rudolfensis and H. habilis vs. modern species H. erectus/ergaster. H. rudolfensis and H. habilis: Greater brain size (610-800 cc), more like later Homo sp., Reduced prognathism (so shorter tooth row), flatter face, More bipedal than Australopithecines, Overlap Australopithecines in tooth and body size. H. habilis: Genus has been controversial, Brain size larger, but overlapped with Australopithecus, Clearly bipedal (e.g., large toe aligned w/ other toes), Face and teeth more like Homo, Inferences on social structure and intelligence. H. erectus/ergaster: First obligate, fully committed biped, Larger brained (600-1250 cc), meat-eater w/ more complex tools (axes & cleavers), H. erectus first to disperse outside of Africa, Used fire, likely vocalized (but lacked speech), Relatively recent extinction (w/in 500,000 years).
You should be familiar with the various species concepts we highlighted, their strengths, and also their limitations.
Biological species concept (BSC): groups of interbreeding natural populations that are reproductively isolated; Pros: Most widely used, Intuitive, confirms lack of gene flow; Cons: No asexual sp., fossils, isolated populations, Difficult to apply to hybridizing populations. Phylogenetic species concept (PSC): the smallest monophyletic group amongst a group of populations; Pros: Can be used where BSC can not; Cons: Requires a phylogeny, Need long period of evolutionary independence for monophyly. Morphospecies concept: groups species based on morphological similarities and differences; Pros: Widely applicable; Cons: Can be too loosely or arbitrarily applied, Difficult to apply to microscopic organisms. ALL trying to achieve recognition of evolutionary independent species!
Evolution always favors survival and reproduction.
By looking at the other mechanisms of evolution, we've seen that evolution can, in fact, favor results that are detrimental to the individual. This is likely a major change in thinking for many of you. To think that evolution can lead to harmful results runs counter to what nearly everyone thinks about the process. It can favor an increase in frequency or maintenance of harmful alleles, it can favor reduced genetic variation, it can lead to inbreeding depression, it can run opposite to the effects of selection (such as through migration or drift).
What might you expect to see different in our species if you could time travel to 1 million years from now? Speculate on how natural selection or other evolutionary mechanisms might continue to influence humans (informed speculation, not wild speculation).
Clearly our modern society has fewer barriers to migration, suggesting greater homogenization of the gene pool will continue (barring cultural barriers). The exception might be some populations that remain isolated and small. They have and will continue to experience some degree of drift and NR mating. With modern advances, certainly the intensity of selection is diminished, but we also have a larger population size that needs resources, poverty, and is experiencing novel changes in our environment (pathogens, toxins, diseases, global climate change, etc.). So although we may be seeing selection relaxed in some ways, it may be "ramping up" in other regards. Whether weak or strong, natural selection will always be present, however. There are countless examples. Others include evidence of stablizing selection on some quantitive characters such as birth weight; and also some evidence of bimodal selection on fertility relative to IQ, and little evidence of directional selection on most physiological, physical, or mental traits (that is, there has been no evidence for selection for bigger size, better physiology, greater intelligence, etc.). So humans should continue to look and act the same at least for the foreseeable future. In several millions of years, however ... who knows???
dispersal
Colonization of a new habitat
What is that "mystery of mysteries?"
Darwin thought that nat. sel. could explain how species formed (origin of species) but he considered that a mystery.
What is ecological speciation? How does it differ from the other forms of speciation we discussed?
Ecological speciation: divergent selection (whether natural or sexual) is the mechanism for reproductive isolation. Two populations might be evolving and adapting to two different environments, favoring reproductive isolation because selection is "pushing" them in different directions. Populations may be allopatric or even sympatric, what is being stressed is that a mechanism (natural or sexual selection) is driving divergence and isolation. sympatric speciation simply emphasizes the LACK of overlap between populations. When we start considering mechanism-based models, such as ecological speciation, we're simply not placing a strong emphasis on geography. Ecological speciation could occur between allopatric, peripatric, parapatric, or sympatric populations. The key point is that the EMPHASIS is on the mechanism of genetic divergence (e.g., natural or sexual selection). Allopatric: geographically isolated pops. Peripatric: a small pop. isolated at the edge of a larger pop. Parapatric: A continuosly distributed pop. Sympatric: within the range of the ancestral pop.
Evolution is a theory about the origin of life
Evolution does have implications for life's origins (e.g., where it might have occurred, which organic molecules came first, etc.), much as it does about countless other fields (ecology, animal behavior, microbiology, comparative anatomy), but life's origins is not the central focus. The science of life's origin is sometimes referred to as abiogenesis. As a field of study, evolutionary biology focuses on how life changed after it originated, regardless of how it started. It explains the origin of life's diversity, not the origin of life itself.
Evolution involves progress; organisms always get 'better.' Related: Evolution is goal-directed (e.g., Humans are the pinnacle)
Evolution gives the appearance of progress if you consider the evolution of life from beginning (individual self-replicating & mutating molecules) to gradually more complex organisms. But it's wrong to think that evolution is inherently a process that involves progress, increased complexity, or an inherent drive towards perfection. Natural selection is not so much "survival of the fittest" as it is "survival of the fit enough." Natural selection is an unconscious biological process that merely favors whatever works at the time in the given environmental context, which may favor being simple, complex, large, small, fast, slow ... whatever works. It is nothing more than a biological process, like cell division. Consider research on penguins not being able to smell fish (meat) or cuttlefish not being able to see color.
Individuals evolve.
Examples of change within an organism's lifetime are development, plasticity, or acclimation. Consider Darwin's finches. Individual birds did not change, they merely lived through the selection event and some passed on their genes more than others. Other aspects of "change" such as development, plasticity, or acclimation do not constitute evolutionary change (i.e., changes to the gene pool over multiple generations).
vicariance
Existing population range split into two or more sub-populations by a physical barrier (island formation, rivers, mountains, habitat changes, etc).
Evolution by natural selection leads to perfection Related: Everything is an adaptation.
First, as we have seen, fitness is intimately connected to environment; it is relative and requires an environmental context. Second, there are countless constraints and trade-offs. It is NOT the case that anything is possible. There are countless examples of traits that evolve as byproducts. For example, research has shown that the evolution of elastic skin in mole rats has given them immunity to cancer as a byproduct! Often features that evolve as a byproduct are mostly nonadaptive (e.g., shortened tail and coat mottling in the silver fox experiment being correlated to 'tameness'), maladaptive (e.g., the sickle-cell allele in the absence of malaria), or simply not possible due to constraints (e.g., giant insects and the biomechanical constraints of their exoskeleton and physiological constraints of the tracheal system ) or evolutionary history (evolution can only 'work' with what is passed on from the previous generation).
Broca's area
Further analysis conducted on H. erectus, discussed subsequently, reveals that the presence of vocalization rather than effective speech was likely the case. This is revealed by evidence of an increase in what is called the Broca's area in the brain. This is somewhat controversial, but this is an area associated with symbolic communication and executive functions.
How do populations become isolated? Is geography necessary or required?
Genetic drift - sampling error in isolated populations leads to distinct genetic differences. Natural selection - populations experience different habitats, competitors, predators, use different resources, etc. Sexual selection/assortative mating - populations evolve differences in how individuals choose, compete for, or attract mates. Mutation - genome duplications and chromosomal mutations isolate populations or facilitate divergence. No! In principle, any of these can lead to speciation. However, genetic drift is thought to play a very minor role. This is supported by empirical and theoretical research. Natural selection is thought to be the major force in causing speciation and leading to the evolution of organismal diversity. Sexual selection is sometimes considered a form of natural selection that strictly emphasizes the ability of individuals to acquire matings. In its most standard form it involves females being selective about their mating partner, perhaps having narrow preferences for certain males, and it also involves males competing for access to females (although the alternative is also possible, females competing and males being choosy). Sexual selection is also very important—some even argue it may be more important than natural selection. One of the reasons for this is because speciation by sexual selection can be very rapid since it is acting on mating directly; for example, imagine a population where an allele frequency change causes females to prefer a different type of male. Selection is acting directly on a trait that is involved in passing on genes to the next generation.
monophyletic
Group of organisms descended from a common evolutionary ancestor especially one not shared with any other group
Why is the name H. habilis controversial? What about H. erectus/ergaster, why are those distinctions controversial?
H. habilis: controversial, because it certainly is the least like Homo than all the others we'll mention (H. erectus, H. ergaster, etc.). Some fossils have shown H. habilis to be more australopithecine-like in body, but more Homo-like in their face and teeth. Other anatomical features, notably brain size (550-687 cc), and also evidence of stone tool use, have favored the designation of this group as being in the Homo genus. Brain capacity ranged outside that of Australopithecus. No clear distinction between H. ergaster and H. erectus; generally most H. ergaster and early H. erectus fossils geographically are confined to Africa. Sometimes, H. ergaster has been categorized as a subspecies of H. erectus, but most researchers consider that too few differences exist to separate them as species. In fact, some researchers deny any validity to the species H. ergaster at all. So for our purposes, we'll just broadly treat them as a group: Homo ergaster / erectus. Homo erectus is generally considered to be slightly more similar to later Homo species. No one argues that these are best represented by a new genus epithet (Homo). Imagine features and behaviors in H. habilis getting more pronounced and more "H. sapien-like," and you have the H. erectus / H. ergaster group.
There's no way we evolved through a random or chance process.
It should be obvious by now that natural selection is the exact opposite of chance; a subset of organisms with a particular trait or traits pass on their genes more than others. This is hardly "chance" or "randomness". The "random" criticism of evolution comes, in part, from the fact that it DOES have random components. Genetic mutation is semi-random in terms of how genetic mutations, where they occur in the genome and how they affect fitness. Genetic mutations are semi-random in the sense that they can occur nearly anywhere, and irrespective of their effect on fitness. Genetic drift is also a random mechanism to evolution, but it is not considered to be a dominant mechanism for evolutionary change. Evolution, and the primary mechanism of change, natural selection, is distinctly non-random.
Are there any traits that make Homo sapiens unique? Or the genus Homo? What are the Oldowan tools? Are there any traits in your assessment that are more unique than others for "making us human"?
Likely there is very little, aside from simple allelic substitutions, that makes us unique. We know we interbred with H. neanderthalensis, some even consider them a sub-species of H. sapiens. It's likely there is very little otherwise. What most people mean when they say "human" is the genus Homo. That's what the book seems to suggest, although if you note in their brief summary, at the end of the chapter (p. 807), they refer to "derived traits unique to our species." By using the word "species," they seem to mean H. sapiens, but much of their discussion in the chapter seems to imply the genus Homo. At any rate, we'll look at features that are unique mostly to recent Homo species. But what IS unique (arguably) in Homo species is the use of complex stone tools; complex in the sense of the tool being modified before use, AND being stone. The earliest stone tool construction and use currently dates to 2.5-2.6 mya from Gona, Ethiopia, and they're known as the Oldowan tools. These tools are widely considered to be from Homo habilis or others that occurred during the same time period and in the same geographic region (e.g., H. rudolfensis). Others have even suggested Paranthropus species may have used stone tools. This information is based on thumb morphology, but it's also been criticized (Paranthropus species have never actually been found with stone tools). The requirement of complexity AND stone together seems rather stringent for a new and unique characteristic. Personally, even if this is true, this seems rather unremarkable for a unique Homo trait. Chimpanzees and even birds have been known to fashion tools for a particular purpose, in other words, make a tool and make it more complex than what it is naturally. Often this involves stripping or breaking twigs or sticks to be of the proper size and shape for extracting food, for example. But other organisms do not fashion stones as Homo species have done. The one problem with this is the suggestion by a minority that Paranthropus may have used tools.
Do you think any of these are "missing links"? Do you agree with that term? How might you respond to criticisms that some of these are merely "apes," mutant humans, or a human walking their pet chimpanzee (i.e., believe it or not, the fossilized Laetoli footprints have been criticized as such).
Many of these species are not exact intermediates between humans and chimps. They just seem unique. They may have chimp-like features, they may have Homo-like features, or they might have Australopithecine-like features. Remember mosaic evolution. But overall, they're their own unique organism. Consider Ardithecus, or H. floresiensis. Or consider Paranthropus species. They have features neither humans nor chimps have. Remember, evolution is not a linear process; these are not chains in a link leading to humans. Think of a bush, with many "branches" representing extinct organisms. It's not always clear to me what critics or the popular media wants with a "missing link." But do any of these fit? What I mean that the co-occurrence is to be expected with evolution, is what I've mentioned in the notes of previous slides. When migration and gene flow are more limited, and populations are smaller and more isolated, as most of our ancestors would have been, it's not a surprise to see multiple, distinct gene pools (greater diversity) coexisting at the same time.
Can you give examples of speciation where geography was not an essential factor?
Mechanism-based model. Laupala crickets: male crickets sing at a particular chirp rate, and females prefer males that chirp at a particular rate. Research shows there is a very strong genetic correlation between male song rate and female preference for that particular rate. In other words, whenever there is divergence in song rate, the preference for that rate also diverges. Since males and females show strong assortative mating (prefer individuals of a similar phenotype), that maintains genetic isolation between populations and favors ultimate speciation.
Wernicke's area (and Planum temporal)
More complex language area; fossil skulls show Broca's area and Wernicke's area enlarge in other Homo. sp.; but asymmetry exists in humans and great apes.
Is evolution always a slow, incremental process? What factors affect the speed of evolution?
No; Generation time, Intensity of selection, Mutation rate (affects the amount of genetic variation); Many different factors can foster RAPID evolution — small population size, short generation time, big shifts in environmental conditions — and the evidence makes it clear that this has happened many times, stronger sel., mutation rate (Viruses).
Misunderstandings of the concept of "species."
Often, the term "species" is not used by evolution critics, but rather, a more vague term is used instead. For example, the term "kinds," which we started off with in this chapter when I showed you a series of birds, along with a reptile or two, and asked you which were different "kinds." One common criticism is that we've never observed a new species form. This statement is simply wrong, for a couple reasons. First, it often relies on a previous misconception that everything in science must be directly observed, which is simply wrong. And in fact, if we use the most commonly accepted definition of a species, the Biological Species Concept, then new species have been generated in the lab. More to the point, often what evolutionist critics are suggesting is that we have never directly observed major transitions between forms, a misconception we've already addressed.
How do populations exhibiting polymorphism, geographic variation, a hybrid zone, or even cryptic species relate to the idea of "species." Can such populations be species?
Polymorphism: (Grove snail (Cepaea nemoralis)), variation in phenotype within a population (therefore variation within the same species); Geographic variation: (bird (drongo (Dicruris spp.)), variation across a geographic region, or across populations, which may have a pattern (Typically when we think of geographic variation we are dealing with the same species, but that wouldn't necessarily have to be the case9; Hybrid Zone: (northern flicker (Colaptes auratus)), 2 different forms interbreed & produce an intermediate form, but remain distinct outside the zone; Crypitc species: (Two-spotted treehopper (Enchenopa binotata)), indistinguishable morphologically, but divergent in songs, calls, odors, or other traits.
postzygotic (inviability, sterility, reduced fitness)
Postzygotic isolation - populations remain isolated even if breeding occurs because offspring are inviable or sterile.
prezygotic isolation (and ecological, temporal, behavioral, and mechanical isolation)
Prezygotic isolation - selection (or drift?) favors mutations that prevent fertilization (formation of a zygote). Ecological isolation: This is when species occupy different habitats. For example, the lion and tiger overlapped in India until 150 about years ago, but the lion lived in open grassland and the tiger in the forest. Consequently, the two species did not hybridize in nature, although they sometimes do in zoos. Temporal isolation: Species breed at different times. Example: Five frog species in the genus Rana occur in North America, but they differ in the peak timing of their breeding activity. So even if they could produce viable, fertile offspring, they simply never mate at the same time. Behavioral isolation: Species don't recognize each other, often this is due to differences in courtship or mating signals. For example, two races of the European corn borer (Ostrinia nubilalis) in the northeastern US use different chemical isomers for their mating pheromone (although still recognized as races, a strong case can be made for species status). Mechanical isolation: Species don't interbreed because of structural or molecular blockage of the formation of the zygote. A silly structural example: if chihuahuas and great danes were "real and wild" animals produced by natural selection, they would be different species; structurally, copulation just doesn't work. Molecular mechanisms might include the inability of the sperm to bind to the egg.
In dealing with the allopatric model, what are the possible consequences should diverging populations come into secondary contact?
Reinforcement: where two diverging forms produce hybrids that have lower fitness. The selection against hybrids would reinforce the pre-mating isolation. Put another way: the individual with the highest fitness in each diverging population would be those who happen to have experienced a genetic mutation that confers a decreased probability in mating with the other "species." Hybrids as third species: Hybrids have higher fitness in new habitat. Hybrids as transitional: Hybrids persist in stable hybrid zone (not new habitat). Essentially have similar fitness.
Evolution is not falsifiable Related: Evolution is too slow to be observed and therefore, relies on faith. Related: "You weren't there" arguments.
See pages 103-105 in your text for some discussion on these and other misconceptions. First, remember the four postulates, each of which is independently testable. Put another way, evolution is most definitely falsifiable. Consider if a mammalian fossil (should only be 10's of millions of years old) was found in Precambrian rock strata (over half a billion years old). Something would be a miss. The two related misconceptions distort how science works. First, they imply that the only valid evidence is that which can be observed directly. So they imply that if we can't directly observe a process that takes millions of years, then it must not be true. But consider if we could only use direct observation as evidence of any phenomenon. We could not study anything historical, or anything too big or small (e.g., atoms, universes). The fact is that we use inferences and indirect observations all the time, in science, in our daily lives, even outside the sciences (e.g., history, law). This equates to a "straw man" type argument that sets up unrealistic and false expectations to cast doubt on evolutionary theory.
Natural selection gives organisms what they need. Related: Evolution involves organisms trying to adapt.
Similar to #6 that says there's no inherent goal or progress, natural selection does not operate on a "need" basis. Organisms do not evolve certain adaptations simply because they are needed. It is not a conscious process and does not involve effort, trying, or wanting. So statements such as, "organism x evolved fur because it needed to stay warm in its cold environment" give an erroneous impression of how evolution works, though such statements are common. Similar inaccurate words include "need," "try," and "want." Natural selection just selects among whatever variations exist in the population. Given the heritable connection across generations, the result is evolution.
Evolution occurs slow and gradually
Some of you might have been initially confused when I first put this up as a "misconception." In general, this statement is true. Evolution tends to be relatively slow, particularly if we're talking about macroevolutionary processes (i.e., origin of higher taxa) and organisms with long generation times. But the key here is that evolution is not always slow and gradual. Consider viral or bacterial evolution (short generation times). Consider the rare genetic mutation that can duplicate a genome and instantly generate reproductive isolation, and therefore, new species. But more generally, even if we have relatively strong selection (natural or particularly sexual) and short generation times, new species of some organisms (those with short generation times) can form in the span of a couple human generations, if not sooner. An example is the apple maggot flies on hawthorn and apple trees. This process has happened within the last 200 years, not millions of years. Remember how people often misunderstand geological time (related to misconception #4) - if Earth's history is represented as an hour on a clock, ALL of human evolution (last couple million years or so) would be represented by the last few hundredths of the last second! Two hundred years in the apple maggot fly is blindingly fast in evolutionary terms.
Are chimpanzees "moral"? (see Franz de Waal video on one of the last slides for insight here)
Studies on monkeys and fairness have shown that given the choice between accepting goodies from helpful, neutral or unhelpful people, capuchin monkeys (Cebus apella) tend to avoid individuals who refuse aid to others (third-party evaluation). Other studies and experiments (see Frans de Waal video) have shown that chimpanzees may even refuse food treats for themselves until another chimpanzee is ALSO given a treat (i.e., recognizes inequity and refuses to be selfish). Why? It turns out that cooperative, even altruistic behaviors can be favored by selection under the right circumstances. Many critics forget, or simply are not aware of evolution having this explanatory breadth.
As populations diverge genetically, at what point might we be able to call them reproductively isolated? What are the various ways in which diverging populations might become isolated? Is it possible for populations to mate, still produce offspring, but yet still be considered separate species?
Subsequent divergence would then occur through other mechanisms, such as natural selection, sexual selection, or genetic drift. The mechanism is typically natural selection, but it could be sexual selection (form of natural selection that emphasizes mating), or even random genetic drift. Reproductive isolation (i.e., full speciation) may occur while the populations are isolated, or it may occur at some point later if they come into secondary contact. Yes! What happens when diverging populations come into contact again (i.e., become sympatric again)? If are reproductively isolated, that means that either they can't interbreed, or if they do, the offspring are inviable in some way. So the fate of speciation is intimately tied to what happens with hybrids.
Evolution is "just a theory," and it is in crisis.
Technically speaking, this misconception is true, evolution IS a theory. But this is equivalent to saying the notion of germs causing disease or objects falling to the Earth when dropped are "just theories" (referring to germ theory and the theory of gravity). Common usage of "theory" implies an untested, speculative idea, like an untested hypothesis. Many people use the term in this way, even some scientists in casual conversation, despite it being technically incorrect. But this also is how critics of evolution use the word, in an attempt to equate evolution with an untested, unsupported idea. However, the precise scientific meaning of theory is that it represents a broadly unifying set of statements based on abundant evidence and reason. Hence, "atomic theory," "big bang theory," "cell theory," or "germ theory." A scientific theory goes far beyond a hypothesis, even a well-supported hypothesis. A true scientific theory provides a more comprehensive understanding of nature and has no credible evidence against it. So yes, ironically, evolution IS a theory, but not in the sense critics often imply.
Okay, maybe organisms can change a little, but I don't see new kinds of organisms evolving. Related: Misunderstand the immensity of geological (evolutionary) time Related: Belief in microevolution, disbelief in macroevolution.
The argument being made here, in a nutshell, is that since we have never directly observed one "kind" change into another "kind," there is no evidence for evolution. Often critics fail to define precisely what they mean by "kind." If they mean species, this has been observed directly in the lab, with fruit flies for example. Generally critics use "kind" to mean a designation above the species level, such as humans evolving from social primates, or birds from theropod dinosaurs. Since we do not live long enough to observe these large-scale changes directly, critics suggest there is no evidence they happened. This argument neglects the fact that evidence in science and many other fields may be direct or indirect. It seems unreasonable to claim there is no evidence of the Revolutionary War since no living person was alive to observe it directly. Or how could we study archaeology? Geology? Or nobody would seriously entertain the notion that atomic theory is false because we have never seen an atom, particularly when we can build rather wicked bombs based on what we have inferred to be true. Similarly, evolution is not falsified because we do not live millions of years to view major evolutionary transitions. We infer major transitions based on abundant evidence from multiple scientific fields. Observations can be direct or indirect, and science uses both in conjunction with reason, empiricism, and a willingness to try new ideas when current explanations lose explanatory power.
mosaic evolution
The discovery of Australopithecus sediba was an exciting discovery, because it represented what some believed a transition from Australopithecus to more derived Homo species. It also showed a mosaic of ancestral and derived features; so-called "transitional fossils" should show a mix of ancestral, derived, and even novel traits. Just the hand of Australipithecus sediba showed that, with features more like their Australopithecus relatives, others more like later Homo species, and some, like the length of the thumb, that were entirely unique.
Laetoli prints
The prints were preserved in wet volcanic ash, presumed to be a male and female walking side by side.
lactose
The sugar present in mammalian milk. It's a relatively complex disaccharide that needs to be broken down into its components, galactose and glucose, in order for our body to use it. In all non-human mammals, AND in most humans, individuals lose the ability to break down lactose after weaning. Individuals become "lactose intolerant" after weaning. But in some human populations, "lactose persistence" has evolved. Instead of being "turned off," there are alleles that remain active into adulthood.
Taxa that are adjacent on the tips of a phylogeny are more closely related to each other than they are to taxa on more distant tips.
This is more of a technical misconception, rather than a common misconception in the public, but it's useful to make it explicit as you study phylogenetics.
Developmental changes (acquired traits) are passed on to an individual's offspring. Related: Confusion over adaptation, development (plasticity), acclimation.
This is very similar to misconception #5, but made more explicit and highlighted to correspond to this chapter. See the brief discussion to #5, in ch. 3.
There are no intermediate forms. I've never seen a creature that's half-man, half-ape.
This misconception is rooted in several factors. First, many misunderstand the concept of a transitional form. Evolution critics often posit ridiculous hypothetical creatures that are better placed in a book on mythology than biology (e.g., the 'crocoduck' of internet fame). Then their claim is made more ridiculous by assuming the nonexistence of such mythical creatures disproves evolution. Second, many expect a transitional form to appear suddenly, like a bird emerging from a reptilian egg. Third, many expect well-preserved fossils to be abundant and widespread, despite the conditions under which fossils are formed being stringent and restrictive. Fourth, many people have the false, preconceived expectation of there being discrete boundaries between different "kinds" of organisms, such as "reptile," "bird," "fish," or "human." In reality, anyone who has studied the diversity of life will tell you these boundaries are artificial, man-made, and better viewed as a continuum, rather than a discrete boundary. More realistic expectations should be that "transitional forms" (not "missing link") should represent a mosaic of features, from those similar to ancestral organisms, to those more similar to their descendants, to those that might be entirely novel. Thus we expect transitional forms to be distinct organisms with an amalgam of features. For example, the famous Archaeopteryx has bird-like features such as feathers, a "wishbone," an opposable big toe, and a bird-like hipbone. It also has reptilian characteristics such as the lack of a true bill (particularly the horny covering called the rhamphotheca), unfused vertebrae, claws, teeth, and a long bony tail. It represents an ancestral form of the "bird lineage," a "proto-bird" that is neither fully avian nor reptilian. It is transitional. In some cases, a collection of fossils do reveal a crude transition, such as larger brains in hominins, gain of feathers in dinosaurs and birds, or the movement and fusion of nostrils to form a blowhole in whales. But in general, evolution is not goal-driven (teleological).
Evolution leads to immoral behavior Related: 'Struggle for existence' does not give justification for "social Darwinism."
This misconception is sometimes related to the "survival of the fittest" phrase. The idea is that if evolution is only about survival of the fittest, then that means evolution is strictly about everyone being for him/herself, the whole process is inherently selfish, etc. This ignores the fact that it can be beneficial to individuals (i.e., "selfish," or better, "self-interest) to cooperate and help others. In other words, what we might deem as moral behavior, helping, cooperating, respecting, and being kind to others can most certainly evolve. In fact it has evolved countless times in everything from microbes to primates. This misconception ignores the fact that individuals might get a reproductive benefit, either directly or indirectly, by cooperating with others, whether it is kin, tribe members, colony members, nestmates, or whatever. A hundred years ago or more the notion of "survival of the fittest" was even misconstrued by some to support the idea of "social Darwinism." This is the preposterous and socially abhorrent idea that if evolution is about survival of the fittest, then the poor, sick, or less fortunate members of our society could justifiably be deemed the "less fit" members of our society. Therefore, we have "biological justification," for making sure their genes do not get into the next generation. Or to compound it, some have used this idea to suggest that those deemed "more fit," such as the wealthy, privileged, and healthy individuals should be favored. This is absolutely NOT what evolution is about, what it suggests, nor what it supports in any biological sense. Thankfully, this is no longer advocated today (mostly).
reinforcement
This would be where the two diverging forms produce hybrids that have lower fitness. The selection against hybrids would reinforce the pre-mating isolation. Put another way: the individual with the highest fitness in each diverging population would be those who happen to have experienced a genetic mutation that confers a decreased probability in mating with the other "species."
geographic isolation
Two populations of the same species become isolated geographically due to some barrier to gene flow, which could be as small as a road, could be human-induced such as deforestation, or it could as large as a river, mountain, ocean, change in current
cooking hypothesis
Unique to Homo; uses of controlled fire favored big brained, tall, upright; get evolution of culture, cooks out pathogens, get more protein; cooking is the major driver of features that make genus Homo unique (found rocks with chips in cave).
theory-of-mind
Unique traits to H. Sapiens; higher cognitive ability; beliefs, worries, stories
We evolved from apes (or monkeys). Related: If humans evolved from apes, why are apes still around?
We are close relatives, cousins, we did not evolve from modern apes (or make the misunderstanding worse, monkeys). To help you understand why this statement is false, picture your family tree. If this statement was true, it would be equivalent to your cousins giving birth to you (which hopefully is an absurd statement). Or worse, it would be equivalent to us expecting our cousins to "disappear" when we are born, because we came from them. Chimpanzees and humans are close evolutionary cousins. The organism that gave rise to us (or gave rise to BOTH chimps and humans via a speciation event), was neither chimp nor human. It was its own distinct organism, perhaps with its own unique constellation of traits, some of which may have been more chimpanzee-like, some of which may have been more human-like, some of which may have been entirely novel. Perhaps it was similar to some of our anthropoid species we studied: Ardipithecus ramidus? others? We do not know for sure, but it wasn't our evolutionary cousin or anything that currently exists.
How does speciation relate to micro- and macroevolution?
We can think of speciation as a micro-evolutionary process (e.g., the effect of natural selection within and between populations), but also as the starting point for macro-evolutionary patterns, such as an ancestral reptile into bird, or an ancestral mammal into a whale (and therefore, the generation of species, genera, families, etc.). The only significant difference between micro- and macroevolution is time. The same mechanisms are at work (natural or sexual selection, genetic drift, mutation providing the raw material, etc.).
Humans are no longer evolving Related: We are no longer "struggling for existence."
We dealt with this one in our evo-bits, and we most certainly are still evolving. The notion that we are no longer experiencing natural selection has a fragment of truth to it. As a species, medical and technological advances have decreased the intensity of selection ON SOME TRAITS relative to our ancestors. The increase in offspring survival is an obvious example. But this doesn't mean we're not evolving. Our environment is still changing, and our genome is still responding to it with heritable change (or changes in allele frequencies) that affects our survival and reproduction. That's all that is required for evolutionary change. Recall Nesse and William's ch. 10 on Diseases of Civilization. In fact, I think one could reasonably argue that in other ways, we are making natural selection more intense, for example, with our rapidly increasing population, multi-drug resistant pathogens, or new diseases being transported around the globe with our vastly increased ability to "migrate."We are most certainly still evolving, we just have to clarify our expectations. Even in a million years, if we're still around, we will likely look quite similar. Perhaps we'll be slightly shorter, experience slight changes in our life history traits (age of first reproduction, etc.). Our divergence from chimpanzees has been estimated to be around 5-6 million years ago. Assuming our common ancestor with them was some transitional form with an amalgam of chimp/human/novel traits, it is safe to say that we have not changed in shocking or dramatic ways in 5.5 million years ago. That being the case, it's likely we won't change significantly in another million.
Compare/contrast geography-based and mechanism-based explanations for speciation.
What is being shown here is geographic variation, or variation across populations relative to geography. Sometimes that variation may show a distinct pattern (clinal variation, e.g., north to south, east to west, or whatever).
What is a "kind"?
When we generally think of different "kinds" of organisms, most people tend to associate the word "kind" to a much higher taxonomic level than "species," perhaps the order or class level if we're dealing with vertebrates. The exception with this pattern comes with greater knowledge of the organisms. Studies have shown that if you ask members of primitive, isolated human population about different "kinds" of organisms in their surroundings, they tend to associate different "kinds" with different species, presumably because they know their native animals so well. Similarly, if you were to ask a bird biologist the same question using the pictures here, he or she would probably ask what is meant by the word "kind," or he or she would at least associate the word with a more exclusive taxonomic level, likely "species." The point here is to get you to think about what the word "species" is trying to do: it's trying to discriminate something real in nature. Boundaries for higher taxonomic levels, such as how we distinguish different genera, are really just arbitrary boundaries. But different species is thought to be a real biological phenomenon. We just have a hard time defining it.
reproductive isolation
Where diff. species may live in the same area but properties of them prevent them from interbreedinng
Genetic mutation only produces harmful effects and "genetic monsters"
With this misconception I want to explicitly clarify common expectations with respect to the word "mutation." In the vernacular we tend to think of "mutation" as a change for the worse, and often a dramatic change. Even when applied to modern biology, I would venture to say that the general public probably thinks of "genetic mutations" that cause major pathologies or diseases. But when we look at the reality of how our genome can mutate, and how those mutations affect evolutionary fitness, we arrive at a very different notion. It should be clear from our study of chapter 5 that the most common form of genetic mutation is a change in a single nucleotide base of a DNA sequence, and most of the time, these changes have very slightly negative or neutral effects. In the right environmental context, however, some can have beneficial effects, and it is the accumulation of these over evolutionary time that largely drives evolutionary change. More dramatic and sudden genetic mutations are possible (e.g., genome duplications), they're just less common.
prognathism
the lower face extended beyond the eyes. This is stronger in chimps and much reduced in us. What may have caused the reduction is an increase in chewing efficiency, relative to chimpanzees (and even more so in more recent hominins).
What does it mean to say that species are "evolutionarily independent?"
they're the smallest independent evolutionary unit
