Lecture 2: History of Evolutionary Theory and Background Biology
Published 2 years ago
Published 2 years ago
- Hypothesis started in Arab and Greek areas, and then moved to England.
- Lyell is the father of geology. He didn't create the ideas, but rather summarized and revised them.
History of Evolutionary Theory
- A change in the genetic structure of a population from one generation to the next. The term is also frequently used to refer to the appearance of a new species.
History - Necessary Background Developments
- Experimental science and hypothesis testing.
- Uniformitarianism is the concept that processes that happen in the present (ex. flooding, volcanic eruptions, everyday snow melt, etc.) can be used to explain deposits from the past. Not catastrophism which states changes in the earth are due to sudden violent random events.
- Lyell observed that earth is millions of years old. At that time, everyone thought it was only some thousands of years old. This way there is an explanation for the time needed for development of new species (a group of organisms that reproduce with each other to produce viable offspring), fossilization, geologic processes etc.
- Linnaeus created the first taxonomy classification system where humans were included with groups of animals. This was a very radical idea at that time, because humans were known as superior and were always acknowledged as separate. 'Homo sapiens'.
- Recognized the change within species over time (as opposed to fixity of species, stating that all species came onto the earth as they appear now, which is the argument by creative design).
- Lamarck attempted to explain evolutionary processes, stressing the effects of environmental change.
Darwin-Wallace - Evolution by Natural Selection
- Lamarck coined the term biology, which is the study of living organisms with evolutionary change as the central concept.
- Lamarck said inheritance of acquired characteristics requires variation to arise when it is needed. He thought an organism could acquire characteristics in its lifetime.
- Darwin-Wallace was the first to mention that evolutionary change happens by natural selection, which states that evolution requires that variation already exists. The theory of natural selection is a mechanism for evolution, explaining how it could happen. States that differential reproductive success in individuals leads to changes in the population. Natural selection affects the individual, but the evolutionary change happens to the population. (Page 30 - 31).
- Acquired characteristic cannot be inherited
Summary of Mechanism of Evolutionary Change by Natural Selection
- For natural selection to occur,
- The trait must be inherited.
- There must be a variation in the trait within the population.
- Fitness (the ability to produce offspring) is a relative measure, since it changes as the environment changes.
- Ex. Galapagos finches, Darwin's theory. Page 32, figure 2.10. Birds that had big beaks used if for getting hard seeds, while smaller beaks were used for fruits. The population shifted during the drought years, where fruits died off which left only hard shell food left. So the large beak birds survived and produced offspring who also had big beaks. The relative percentage (frequency of alleles) of beak size changed in the population, so evolution occurred.
- Ex. Peppered moth in northern England. Page 31-32, figure 2.15. Before there was a lot of white bark, so white winged butterflies survived because they were able to hide from their predators. But in the industrial revolution, soot covered the trees and made them dark. Over time, the allele frequency changes so that darker winged butterflies survived and reproduced.
- Ex. Bacterial resistance. Page 32.
- Ex. Giraffes. Figure 2.3.
- But reproductive fitness and success is not only about survival of individuals. Includes reproduction to produce offspring and survival of offspring to reproduce. Differential net reproductive success.
- Ex. Swifts and their offspring. Page 33-34. Swifts can have 2, 3 or 4 eggs. The most successful fitness is 3 eggs, because there are not too many offspring to take care of.
Background Biology (Cells)
DNA - Introduction to Genetics (Chapter 3)
- Chromosomes are a group of DNA molecules.
Two Types of Cells
- Somatic cells are body cells, each having 46 chromosomes which are grouped into 23 non identical pairs in humans.
- All somatic cells in organisms have the same genetic information. They all have the ability to make all types of cells. But all cells have some parts turned off, so that only the part that is needed is used. Regulatory genes turn on the right part of DNA by sending a message. If the regulatory genes get messed up, they will give the wrong message. This is very important for evolution and also for medical research.
- Gametes zygote. Gametes are reproductive cells, eggs and sperm. They have 23 chromosomes in each cell in humans, one from each pair of 46 chromosomes. All non identical. Two gametes from two different individuals unite to form a zygote, which has 46 chromosomes by the end.
DNA (Deoxyribonucleic Acid)
- Structure (Figure 3.2). There are two strands that form a double helix, called a backbone. There are a series of linked bases, AT CG pairs.
- Replication (figure 3.3). DNA is the only molecule responsible for the transmission of traits and the only molecule which can replicate. The two strands of DNA are unzipped by enzyme. Each strand is a template for a creation of a new strand bonded to it.
- Protein synthesis (coded with mRNA, page 40-42). U instead of T in base pairs. Proteins are used by the body in many ways. We eat proteins which get broken down into amino acids. They form the proteins into something our bodies can use. DNA says 'here is how proteins go together to come in use'. Codes in groups of three, which make up amino acids. The order of the amino acids determines what protein it is.
- The triplet codes for amino acids are the same in all organisms. The difference is of order of codes which creates diversity.
- A gene is the sequence of DNA that specifies how to build a protein.
- Regulatory genes produce proteins that influence other genes in their own production.
- A mutation is a change in the DNA. The sequence of bases or a change in the structure and number of chromosomes.
- Genes and mutations are important in creating proteins. They are very important in the body's functions, in creating the structure of organisms, influencing communication and have a big effect on the regulation of systems