Lecture week 1 (8-24) - Notes Introduction to Evolution

Biol 114 Fall 2023

Week 1: (8/24)

Intro To Darwin and Evolution
For a long time, before the mid-1800s, the world new many important ideas about variation, species diversity, and species change. We knew:
1. Organisms have offspring similar to themselves.
2. We could select individual plants and animals on our farms to breed and produce offspring that we considered beneficial.
3. There exists a large amount of diversity/variation among organisms within a species.
4. Differences among the members of a population mean that not all are affected in the same way by ecological factors
5. The variation between species may mean that not all areas that can do so will support a population of a particular species or actually have a population present.
6. Typically, individuals produce more offspring than what the environment can support.
7. We also believed:
  1. All organisms were created by a divine being (Special Creation) as recently as 6000 years ago.
  2. Species have never changed and are unchangeable.
  3. Aristotle’s Great Chain of Being: All species are organized into a sequence based on increased size and complexity, with humans at the top.
  4. Variation between individuals is unimportant or misleading.
Jean-Baptiste de Lamarck –
1. First to state that species have changed through time (first formal evolutionary theory).
2. Thoughts were based on Aristotle’s typological thinking and simple organisms spontaneously generated.
3. Species change through time via acquired characteristics – That is, individuals change as a result of environmental pressures and then pass those traits to offspring. (Giraffe neck, and my son as examples)
Along comes Darwin

Although Charles Darwin and Russel Wallace independently came up with the theory of evolution by natural selection at roughly the same time, Darwin’s name is more typically associated with its creation. As a result, from here on when talking about evolution, we will refer to Darwin only.

While traveling on the H.M.S. Beagle around the world from 1831-1836, Darwin amassed a huge amount of evidence that there existed a tremendous amount of variation within species, between similar species, and between distinct species. He also noticed that the traits organisms had seemed to change and be predictable based on differences seen in environmental factors like weather, climate, geology, etc.

As a result of the accumulation of this evidence, Darwin went on to publish his now-famous book: On the Origin of Species. Within this and subsequent books, Darwin concluded:

Variation, in conjunction with environmental pressure, is the key to understanding diversity and how and why species change.
Darwin’s theory on the Origin of Species by Natural Selection had 3 components:
- 1. All species have a common ancestor.
  2. All species show changes in characteristics through time.
  3. All species show changes in characteristics in different environments.
These three (esp. the 3^rd) lead us to our Modern Theory of Natural Selection
Modern Theory of Natural Selection
1. Evolution is the change in genetic (allelic) frequency within a population over time.
2. Natural Selection is a process by which evolution can occur.
3. Natural Selection requires:
  1. Trait variation in a population. Variation is the fuel of natural selection. Without it there are no traits to select for and against. Future generations will be no different than previous generations (minus genetic drift). Almost all phenotypes have variation. These exist on a continuum, not normally an either/or situation.
  2. Heritability. The traits in question need to be heritable, that is, passed from parent to offspring by genes. This is where Lamarck’s ideas fell apart. Acquired characteristics are not normally passed from one generation to another (However, pay attention when we get to the end of “Mendelian Inheritance”.)
  3. Differential survival. There needs to be a difference in survival to reproductive age based on the condition of the trait (which leads to Differential reproduction below). Some individuals will produce more breeding offspring than others will. Non-breeding individuals are no different than dead individuals. Differential survival also refers to differences in the persistence of genes (traits) across time within a genetic line within a population.
  4. Differential reproduction. As a result of a condition of the trait, individuals will have more breeding offspring than others, thus passing the genes for that condition into the next generation

As a result of the greater survivorship and reproductive success of individuals possessing a particular trait, they are considered to be “naturally selected”, i.e., selected to survive in nature because of the traits they possess. Remember, it is the relative number of breeding offspring that counts: a king salmon producing 100 eggs is not very good when its neighbors are producing thousands! The individual producing more offspring is considered “more fit”. Fitness, here, refers to the number of viable offspring you produce in your lifetime. “Survival of the fittest” (a line so often quoted, but not understood) does not refer to the strength or constitution of an individual, but how many offspring that individual can produce or potential fitness – how many offspring can they produce. They often mean the same thing, since those that are bigger and stronger frequently have more offspring, but this does not always work. Actually, I don’t remember ever hearing a biology professor use the term “Survival of the fittest”. Maybe because it frequently means something else entirely to the non-scientific community, scientists have steered clear of using it.

1. Where are the 4 components of NS in the example of your sinus infection (from the video lecture provided)?
2. Natural selection results in traits that are selected for. Adaptations.
3. Adaptation is:
  1. A heritable trait that increases the relative fitness of individuals having the trait.
  2. A process by which individuals within a population acquire traits that increase their relative fitness. Here, one organism can be “better adapted” to a particular environment because the process of “adaptation” has taken place over a longer period of time. The term “adaptation” as a process is similar to “natural selection”, although “adaptation” implies the formation of a fitness-enhancing trait rather than what/how selective agents operate.

Artificial Selection

Having defined a mechanism of genetic change in a population over time as Natural Selection, you would think there must be such a thing as Artificial Selection. Indeed there is. Artificial selection is a similar process to natural selection. In the case of artificial selection, however, the selecting agents (that which drives the evolutionary process) are humans. For thousands of years, people have been selecting individuals from their domesticated stock of plants and animals to breed. These organisms have been selected because they possess some desirable trait (e.g., high food yield, ability to assist humans, etc.), and the resulting offspring would continue that trait as well. This sort of selection is considered “artificial” because the selective pressure is not occurring as a result of non-human environmental conditions, and, more importantly, the resulting desirable traits do not necessarily allow the individuals to survive and reproduce more offspring in the wild. That is to say, the resulting traits are not adaptive in the wild, even if they are so in captivity.

II. Evidence for Evolution

There are three main conclusions from evolutionary theory. 1) Species are related, 2) Species (and species diversity) change over time, and 3) Evolution should be able to be seen in the short-term. The first two of these, are typically referred to as Macroevolution, the change of one major taxonomic group into another (e.g., fish to amphibians to reptiles), or the creation, or extinction, of species. The third is often referred to as Microevolution, the change in a population over generations that helps to separate populations from each other genetically. The accumulation of microevolution over a long period may result in the creation of new species (macroevolution).

Macroevolution
1. Evidence that some species are related.
  1. Geographic proximity of similar, non-interbreeding species. The birds in the figure (in the video) are 4 different species of mocking birds on the Galapagos Islands. Their extreme similarity and close proximity suggest relatedness.
  2. Homology – similar traits in separate species due to a shared common ancestor
    1. Genetic Homology - similar gene sequences between individuals of different species.
    2. Developmental Homology - similarities in morphology of embryos of different species.
    3. Structural Homology- similarities in structure of body parts of different species.
2. Evidence that species (and species diversity) change over time.
  1. Fossil Record
    1. Not all species were together at one time
    2. Extinction has taken place
    3. Transitional forms exist
    4. Major increases in species complexity takes billions of years
    5. Life began in the sea
  2. Vestigial Traits structures in organisms commonly found in the species that serve little or no function (as compared to an Atavism – a vestigial trait found in very few individuals within a species).
Microevolution

We have already considered many aspects of microevolution. Consider the case of antibiotic resistance in the example of you fighting your sinus infection.

III. Misconceptions about Evolution

Probably no other biological concept has generated as much controversy among the non-scientific community as evolutionary theory has. The unfortunate reality of the situation is that many of the problems people have with evolution are largely based in inaccuracies and misconceptions. Worse still, once these inaccuracies are used in arguments against evolution, either in private or public settings, the listeners believe them and use them in their own arguments. What follows is a list of commonly held misconceptions about evolution.

1. If evolution is true, then there is no God.
2. Humans evolved from apes.
3. Individuals evolve.
4. Adaptation occurs because a species needs/wants it.
5. Evolution always results in a more complex or better organism
6. Animals do things for the good of the species
7. All traits are adaptive
8. Functional traits have unlimited adaptive potential

IV. Evolution as a scientific framework

Apart from explaining how species are related and how species have changed over time, evolution provides us with a scientific framework within which we can investigate the world around us. Science is based on testable, rejectable hypotheses. Evolutionary theory allows us to predict events (form hypotheses) within biological systems as well. We can then design experiments to test for those events, and, thus, better our understanding of our world. Consider the example of Homicide (Daly and Wilson 1988) in the lecture video.

V. Evolutionary trends.

There have been some long-term trends that resulted from macroevolutionary processes over billions of years. These include:

1. An increase in multicellularity
2. An increase in complexity
3. An increase in ways to capture energy for use
4. An increase in ways to deal with the environment - biotic and abiotic
5. An increase in diversity (snowball effect)

Note