Lecture: Correcting Misconceptions About Evolution

Avoiding Misconceptions: Some Important Points on how Evolution Does and Does Not Work.

NOTE: These are lecture notes for Biology 391, Organic Evolution, at The University of Tennesee at Martin. Anyone outside of UT Martin wishing to use these notes or to contact me for additional information should first read the information obtained by clicking here.

Goals: The goal of this lecture is to emphasize some important points about how natural selection and evolution do and do not work to help you avoid some of the common misconceptions about evolution.

Related Textbook Material: Freeman and Herron (2001) Chapter 3 sections 3.3-3.5

Lab Manual Questions over this material are in Lab Manual Chapter VII

The Lecture:

Many misconceptions about how evolution works are commonly found in nature shows, the popular press, etc. As a result, figuring out how it actually works can be confusing; you may have ideas about how it works that are not correct and that will confuse you. In this section, I'd like to stress some points about how natural selection and evolution work to help you avoid some of these common problems.Some important points to note about natural selection.

Differences in fitness (survival and reproduction) generally depend on how well individuals with certain traits can function in their specific environment. A trait might have high fitness in one environment and low fitness in another. For what trait in peppered moths is this true? For what aspects of HIV is this true?
adaptation (evolution through natural selection) is something that happens over many generations. If one individual's phenotype (appearance) is modified within its lifetime, that's NOT adaptation. Individuals do NOT adapt. If an individual has a genetic trait that results in low fitness (for example, a gray peppered moth in a black woodland), that's tough luck for that individual; it won't change (it will probably be eaten.) It is populations that adapt as genetic traits that result in high fitness in individuals become more common.
natural selection does not occur in order to benefit a population or a species. Natural selection occurs because some individuals (NOT SPECIES) survive better than do others, and reproduce their traits better. This MAY result in improved survival of the species -- for example, if a trait evolves because individuals with it can obtain food better, this may be good for the species -- but may not; for example, a trait that improves the ability of individuals to obtain food might cause populations to reproduce rapidly, overpopulate their environment, and die out (this would be bad for the species.) The point is that traits that improve individual survival evolve regardless of their impact on the population or the species; whatever impact they end up having on the population or species is a side effect of this process.

Now let's consider some more important points about how evolution does (and does not) work:

evolution has no goal. Evolution occurs because of variation that exists within species; this variation arises randomly through mutation, as we will discuss in more detail later. It can not magically look into the future and plan for the future.
no extant (modern, currently living) species can be considered to be evolutionarily more advanced, or higher, than others. All life that exists on Earth apparently evolved from a single ancestral species, so all species that are now alive have been evolving for the same amount of time. All species have some traits that are recently evolved and some that go back very far in evolutionary history. All species show adaptations to their particular environments. We tend to think of ourselves as advanced and of organisms like bacteria as less so, but evolutionarily we can not rank species in this way; we have some traits, such as our large brains and intellectual abilities, that are recently evolved, but have others, such as the way our genes code for proteins, that trace back to the ancestor to all life. Similar, a bacterium may have an advanced, recently evolved trait such as the ability to resist being killed by an antibiotic (something that evolved only after we started treating them with antibiotics) and also have the same way genes code for proteins that we do and that traces back to the ancestor to all life.
no modern species is the ancestor to any other modern species. Modern species are related -- if you trace their ancestry, you find that at some point in the past they evolved from some common ancestral species -- but since the descendent species continue to evolve we consider them to be different species from that common ancestral species.
natural selection does not necessarily make organisms more complex. Again, we tend to think of ourselves as complex and advanced and assume that natural selection results in the evolution of these traits (because they work well for us,) but in some environments it is better to be less complex and in such environments complexity decreases through natural selection. For example, eyes have been lost in species of fish and salamander that live in completely dark caves; they serve no function in darkness, and to make them wastes energy, so NOT having eyes has higher fitness than having eyes in a dark environment.
natural selection does not always result in species that are perfectly adapted to whatever the current environment is. Natural selection occurs based on the variation that is present in a species at any time. The traits that are best adapted may not have arisen through mutation; in that case, they will not have evolved. The environment may also have changed recently; in this case, species are likely to be adapted to a previous environment, not the current one. We will consider other reasons natural selection does not always result in perfect adaptation later in the term; for now, it is just important for you to begin to recognize that species are not all perfectly adapted.

At this point, you should be able to answer the questions in section V of your lab manual. Work on these questions to make sure you understand and can apply the different points discussed in this lecture, and are avoiding potential misconceptions about evolution.

Study Tips: start to be careful whenever you discuss or write about evolution (for example, in study questions, on papers, or on exams) to be clear when discussing adaptation that you avoid the misconceptions discussed here! The material from this lecture applied to EVERYTHING in this course, and you will lose credit if you do not avoid these common problems! In particular:

be careful of the word "individual" and never imply that an individual can adapt.
when discussing fitness and adaptation, refer to the environment within which a trait has high (or low) fitness, or is an adaptation -- don't just refer to the trait.
be careful of the words "population" and "species" and never imply that traits have evolved for the good of a population or a species.
never say or imply that any modern species is the ancestor to any other modern species.
never say or imply that there is a goal to evolution.
never say or imply that a more complex trait must be more recently evolved.
do not refer to "higher" and "lower" or "more advanced" and "less advanced" modern species.
do not assume, say, or imply, that a species or population must be perfectly (optimally) adapted to its environment.

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