Mutations are the origin of genetic diversity. Mutations introduce new traits, while selection eliminates most of the reproductively unsuccessful traits. Sexual recombination of alleles can also account for much of the genetic diversity in sexual species. In some instances, population size can affect diversity and rates of evolution and fixation, but in other cases population size does not matter.
Genetics controls evolution. There are four major genetic systems, which are combinations of sexual/asexual and haploid/diploid. In all genetic systems, adaptive genetic change tends to start out slow, accelerate in the middle, and occur slowly at the end. Asexual haploids can change the fastest, while sexual diploids usually change the slowest. Gene frequencies in large populations only change if the population undergoes selection.
Neutral evolution occurs when genes do not experience natural selection because they have no effect on reproductive success. Neutrality arises when mutations in an organism’s genotype cause no change in its phenotype, or when changes in the genotype bring about changes in the phenotype that do not affect reproductive success. Because neutral genes do not change in any particular direction over time and simply “drift,” thanks in part to the randomness of meiosis, they can be used as a sort of molecular clock to determine common ancestors or places in the phylogenetic tree of life.
Adaptive Evolution is driven by natural selection. Natural selection is not “survival of the fittest,” but rather “reproduction of the fittest.” Evolution can occur at many different speeds based on the strength of the selection driving it. These types of selection can result in directional, stabilizing, and disruptive outcomes. They can be driven by frequency-dependent selection and sexual selection, in addition to more standard types of selection.
Genetic transmission is the mechanism that drives evolution. DNA encodes all the information necessary to make an organism. Every organism’s DNA is made of the same basic parts, arranged in different orders. DNA is divided into chromosomes, or groups of genes, which code for proteins. Asexually reproducing organisms reproduce using mitosis, while sexually reproducing organisms reproduce using meiosis. Both these mechanisms involve duplication of DNA, which then gets passed to offspring. RNA is a key component in the duplication of DNA.
The lecture presents an overview of evolutionary biology and its two major components, microevolution and macroevolution. The idea of evolution goes back before Darwin, although Darwin thought of natural selection. Evolution is driven by natural selection, the correlation between organism traits and reproductive success, as well as random drift. The history of life goes back approximately 3.7 billion years to a common ancestor, and is marked with key events that affect all life.
In this lecture, Professor Kagan tells the story of the rise of Philip and describes his early actions: unifying Macedon, defeating barbarian armies, and creating a new, professional, national army. According to Professor Kagan, through these actions, Philip was able to make inroads into the Greek world. What made these inroads more effective was Philip’s uncanny talent for diplomacy and the fighting between the various poleis. Eventually, the Greeks under the efforts of Athens and Demosthenes decided to face Philip in the battle of Chaeronea.
In this lecture, Professor Kagan describes the growth of a new power: Thebes. Under the leadership of Epaminondas and Pelopidas, Thebes grows into a major power among the Greek cities. In fact, the Thebans even rout the Spartans in a standard hoplite battle in the battle of Leuctra. Finally, Professor Kagan points out that by the time of Theban hegemony, the Greek world had experienced so many wars and conflicts that it opened the door to a powerful leader: Philip of Macedon.
In this lecture, Professor Kagan examines the continuation of Spartan tyranny over the Greek poleis and the response of the Greek world. According to Professor Kagan, it became clear that the Greek poleis needed to do something to check the power of Sparta. So, Thebes, Argos, Corinth, and Athens along with some of the smaller poleis joined together to fight Sparta in the Corinthian War. The war ended in a stalemate, but now the Persians were afraid of the growth of Athenian naval power.
In this lecture, Professor Kagan describes the aftermath of the Peloponnesian War and how the Spartans began to dominate other Greek poleis, instead of liberating them. The Spartan general Lysander at this point not only grows in influence and power, but also follows an aggressive plan to establish pro-Spartan, oligarchical governments. However, according to Professor Kagan, this fact angered many cities. Therefore, Thrasybulus, along with the help of other poleis, resisted Spartan rule.
