Genetic transmission is the mechanism that drives evolution. DNA encodes all the information necessary to make an organism. Every organism
Principles of Evolution, Ecology and Behavior (Lecture Series by Yale University Professor Stephen Stearns)
- Principles of Evolution, Ecology and Behavior (Lecture Series by Yale University Professor Stephen Stearns)
- MIT Video Courses on Evolution
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.
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.
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
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.
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.
Development is responsible for the complexity of multicellular organisms. It helps to map the genotype into the phenotype expressed by the organism. Development is responsible for ancient patterns among related organisms, and many structures important to development shared by many life forms have changed little over hundreds of millions of years. Development is expressed combinatorially, allowing a relatively small amount of genetic information to be expressed in many different ways.
Reaction norms depict the range of phenotypes a single genotype can produce, depending on the environment. Reaction norms must fit within an organism.
There are several explanations for the evolution of sex evolution and its continued prevalence. One is facilitating the spread of helpful mutations while hastening the removal of harmful ones. Another is expediting resistance against pathogens. Sex does have several costs compared to asex, such as only giving half your genome to offspring, having to find mates, and the risk of predation and STDs. Overall, the benefits outweigh the costs and sex has a firm hold on the majority of the recent branches of the tree of life.
Genomic conflict arises when the interests of various genomic elements, such as chromosomes and cytoplasmic organelles, are not aligned. These conflicts arise in two situations: either when one unit is contained within another, as a mitochondrion is contained within a cell, or when inheritance is asymmetrical. Genomic conflict can thus occur within a cell, within an organism, or between two organisms, such as a mother and developing fetus. There have been several steps taken to avoid these conflicts in sexual species, including the fairness of meiosis and the uniparental inheritance of cytoplasmic genomes.