36-lecture Course: Principles of Evolution, Ecology and Behavior

Lecture #1 of 46

Course Description: Offered by Yale, this is an introductory course by Professor Stephen C. Stearns into the study of biology and the environment focusing on the principles of evolution, ecology and behavior. Recent advancements in the field, in regards to ideas, mechanisms and processes, have set new standards that should be known by all biologists, as well as educated citizens.

The Nature of Evolution: Selection, Inheritance, and History

This lecture takes a general look at evolutionary biology and its two main divisions: microevolution and macroevolution. Darwin was responsible for natural selection — the idea of reproductive success and its ties to organism traits — but evolution also has roots deeper than Darwin. Life can be traced back to ancestors approximately 3.7 billion years ago, and build the history that led us to where to are today.
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Basic Transmission Genetics

Evolution is driven by genetic transmission. Every organism is given all the necessary information it needs by DNA. This DNA is made up of the same basic building blocks as other DNA, but it is the way the blocks are arranged that create different structures. Chromosomes, which are groups of genes that code for proteins, divided up the DNA. If an organism is asexual, it reproduces using mitosis, and if an organism reproduces sexually, it uses meiosis. Mitosis and meiosis both wind up with the same end result, the duplication of DNA (where RNA plays a crucial role), which is passed to offspring.
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Adaptive Evolution: Natural Selection

Natural selection pushes adaptive evolution. Many mistake natural selection as being “survival of the fittest,” but actually is best referred to as “reproduction of the fittest.” Selection occurs at varying rates and can result in several outcomes: directional, stabilizing and disruptive. These outcomes occur due to frequency-dependent selection, sexual selection and other standard forms of selection.
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Neutral Evolution: Genetic Drift

If genes have no effect on reproductive success, then they experience no natural selection and are dubbed the title, neutral evolution. This neutrality emerges as a result of an organism’s genotype mutation causes no change it the organism’s phenotype. Neutrality can also result from changes in the genotype and phenotype that bear no effect on reproductive success. Genetic drift is the term applied to neutral genes because of their inability to change direction over time, and rather “drift” instead. With the help of meiosis, neutral genes are useful as a molecular clock to help identify common ancestors or positions is the phylogenetic tree of life.
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5. How Selection Changes the Genetic Composition of Population

Genetics plays the master role in evolution. The genetic systems are divided into four main parts: the combinations of sexual and asexual, and haploid and diploid. Adaptive genetic change in all genetics systems has somewhat of a roller coaster effect: it begins slow, accelerates, and then finishes slowly. Of all the combinations, the asexual haploids have the fastest rate of change, while sexual diploids generally have the slowest. But in large populations, gene frequencies only change if the population undergoes selection.
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The Origin and Maintenance of Genetic Variation

Mutations are partly responsible for genetic diversity. It is because of mutations that new traits are introduced as selection weeds out the reproductively unsuccessful traits. Sexual recombination of alleles also plays a role in creating genetic diversity. In some cases, genetic diversity and its varying rates of evolution and fixation can be affected by population size.
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>The Importance of Development in Evolution

Complexity of multicellular organisms is due to development. It assists in mapping the genotype into the phenotype. Ancient patterns between related organisms is also due to development, and structures among life forms have experienced little change over the course of hundreds of millions of years. Expressed combinatorially, development allows genetic information to be pronounced in many ways.
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The Expression of Variation: Reaction Norms

Depending on the environment, the spectrum of phenotypes that a singe genotype can create, are described by the reaction norms which must consist within an organism’s phylogenetic constraints. Reaction norms can range from differing in individuals, to some traits differing slightly due to the environments and sometimes there is no difference whatsoever.
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The Evolution of Sex

The evolution of sex has several reasons for its perseverance. The first is the spawn of beneficial mutations while expelling the harmful ones. The second accelerating resistance against pathogens. There are disadvantages to sex though: offspring receiving only half your genome, difficulty finding mates and predator and STD risks. However, the advantages exceed the disadvantages and sex remains the dominant division in reproduction.
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Genomic Conflict

When interests of various genomic elements, like cytoplasmic organelles and chromosomes are not in sync, genomic conflicts occur in two types: either one is enclosed with another, or inheritance is asymmetrical. Genomic conflict can arise within several situations: a cell, an organism or between two organisms. Operations to avert conflicts in sexual species involve uniparental inheritance of cytoplasmic genomes and fairness of meiosis.
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Life History Evolution

There are three main divisions life history defines for traits in organisms: number and size of offspring, age and size at maturity and reproductive investment and lifespan. An organism must find a balance between these traits. Answers to ecological problems, such as food acquisition and mortality, come from life history traits, which are revealed through reaction norms that determine what traits are displayed by an organism when their genes come across certain conditions.
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Sex Allocation

How much reproductive investment an organism decides to pass on is known as sex allocation. Typically, it is a 50:50 ratio, but that can vary. Hermaphrodites are an example of organisms that have a variation of the norm. Some species can even adjust their own sex ratios depending on the conditions of their environment.
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Sexual Selection

Natural selection encompasses sexual selection in the sense that mates are chosen for survival capabilities. Natural selection is commonly known as survival of the fittest, but reproduction of the fittest is a more appropriate term. Sexual dimorphism occurs from sexual selection. Intersexual selection refers to a sex picking a mate, and intrasexual selection refers to individuals of a sex competing for mates. Many times, the deciding sex uses signals to help their decisions.
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14. Species and Speciation

Speciation is course where species depart from one another and/or a common ancestor. Species can be defined a many different ways, but they all mainly focus on two aspects: reproductive isolation and/or phylogenetic similarities. Controversies can arise from this. Speciation occurs from ecological specialization or geographical separation. During speciation, there are times when organisms organize themselves into groups before becoming different species.
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Phylogeny and Systematics

Because appearances can be deceiving, the tree of life is determined through detailed genetic analysis. Just because a species looks similar, does not necessarily mean they are the same or share common ancestors. Determining a correct tree means defining through simplicity and if what we see is probable.
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Comparative Methods: Trees, Maps, and Traits

Phylogenic information can be linked to geographical histories using genetic analysis. Throughout human history we have left genetic traces of our migration scattered about the globe that we can trace all the way back to Africa. Molecular genetic methods are used to determine if trait states were ancestral. These findings can have large implications for biological ideas.
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Key Events in Evolution

Several crucial events have defined the history of live and evolution. Some examples are of symbiosis and specialization bringing biological units together. Other events involve information transmission or conflict resolution all the way up to the cultural level.
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Major Events in the Geological Theatre

Two of the biggest influences on the development of life are geology and climate. Examples of this are the tectonic drift, mass extinctions, oxygenation of the atmosphere and natural disasters. Life, mainly bacteria, has also had a profound effect on the planet’s geological makeup through metabolic processes.
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The Fossil Record and Life’s History

Evolutionary information can be found through fossil records. While historically this information could not be seen on shorter time scales, new fossil records are more thorough. Fossil records show that extinctions create ecological space for which new speciation and radiation can occur. Fossil records also show that life forms start small and increase in size over time.
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Coevolution

Coevolution occurs on not only the level of the species, but on many others as well. Organelles like mitochondria and chloroplasts are good intracellular examples. Other living things are an important part of an organisms environment. Coevolution can happen in helpful ways, such as symbiosis, and in harmful ways, like parasitism. Frequency, degree of interaction, and many others can influence coevolution.
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Evolutionary Medicine

Evolution also plays the part of doctor. It provides a path for how our bodies acknowledge treatments, it helps pathogens respond to treatments, and how these responses will change over time. Often, pathogens with the help of evolution, reach an intermediate level of virulence at which point they can infect hosts and reproduce. But these pathogens are still spread because they are not strong enough to kill the host.
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The Impact of Evolutionary Thought on the Social Sciences

It is said that humans could be part way through an evolutionary transition that separates individuals and groups. Common tensions in modern life could be a result of the two units of selection and the pull between biology and culture. Examples of this struggle are the appearance of selfishness and altruism in our culture.
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The Logic of Science

Just because modern science and philosophy have many differences, it does not mean there aren’t philosophical ideas that can be applied to science. Ideas about the nature of science have led to new thoughts about falsifiability, revolutions, creativity, and have pushed the boundaries of what was thought possible by different types of science.
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Climate and the Distribution of Life on Earth

Physical aspects of the earth’s biomes are discussed. Several factors are introduced: water, latitude, altitude, and temperature. Regions that contain similar similar aspects, typically have similar life-forms. These aspects also can change weather patters which affects habitats and ecosystems.
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Interactions with the Physical Environment

Every species has an environmental range that it can survive in. The most beneficial spot for survival is typically in the middle of this range. When there are complications, organisms can adapt to meet the difficulties of the environment. These adaptations and what can be manipulated differ between plants and animals.
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Population Growth: Density Effects

Population growth is balanced by several factors. Some of these factors are density, food and resources, and predators. Density refers to the probability that one species will run into its own kind and not another species. Mathematics of logs and exponents are used for population growth studies.
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Interspecific Competition

In lower density populations, interspecific competition can often have a greater impact on selection than intraspecific competition. Effects on each species fitness from another can result in positive, negative, or neutral effects. These effects as a result of cohabitation help shape evolution similar to the way the physical environment or species does.
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Ecological Communities

The concept of ecological communities has changed greatly over the past four decades. In the past, it was said so many species were a result of evolution packing niches tightly. But now, trophic cascades are emphasized. Trophic cascades are food chains controlled from the top down. Foods webs were downplayed by this as predation in ecology was emphasized. As a result, interrelated nature of ecosystems were seen as better than food chains.
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Island Biogeography and Invasive Species

An important factor in ecology is geography. To model this, two systems were designed: island biogeography and metapopulations. Metapopulation is the recent but dominant theory. They consist of populations in multiple neighboring areas. If an individual population ceases to exist, the metapopulation still goes on. This application has gained popularity because of its applications to epidemiology.
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Energy and Matter in Ecosystems

Geology, meteorology, and chemistry all come into play when studying the movement of matter and energy around the planet. Energy moves upwards from plants to herbivores to carnivores, and then is decomposed by detritivores, beginning the cycle all over again. Photosynthesis or chemosynthesis is also used to produce energy. Compounds are also important to life and include nitrogen, carbon, and phosphorous.
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Why So Many Species? The Factors Affecting Biodiversity

There are many different viewpoints one can take when looking at biodiversity. An ecological view looks at how necessary diversity is for an ecosystem to function. An economic view looks at how valuable nature’s “services” are for mankind. An evolutionary view artificiality of the human “right” when compared to dominance. And a personal view looks at the emotional values people attach to biodiversity.
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Economic Decisions for the Foraging Individual

Examining the behaviors of organisms can be done several ways. For example, when they forage, hunt, or look for mates. The higher the organism, the more complex the behavior. Foragers and hunters have been known to adjust their behaviors after examining the cost and benefits of an action. They also hoard resources to handle risk.
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Evolutionary Game Theory: Fighting and Contests

Game theory, the idea that your outcomes are affected by the actions of others, can be applied to evolution. If you look at interactions between organisms as not just encounters, but as a mathematical “game,” then information regarding fitness payoffs and proportions of “strategies” played by groups can developed. Even though nature is sometimes much too complicated, mathematical models can still be useful for conveying ideas.
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Mating Systems and Parental Care

Each species varies in their mating systems and the way they care for their young. Factors upon parental care are physical environments and behavioral dynamics in intraspecies relationships. The mating system, in reference to the dominant sex and internal or external fertilization also affects parental care.
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Alternative Breeding Strategies

Males and females differ in their breeding strategies. These differences can typically be tied to frequency dependence. The relative fitness of the different strategies will be similar if the species is at evolutionary equilibrium. Differences can be traced all the way down to the gamete.
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Selfishness and Altruism

Darwin and others originally thought altruism and self-sacrifice could not go hand-in-hand. But new explanations show how an individual’s fitness could be increased by altruism. Kin selection is one of these explanations. Kin selection is the idea that one’s genes can be increased by helping relatives. Another explanation is ecological constraints and punishments. This is where individuals help the group while waiting for their chance to reproduce.
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