Evolution Notes

Unit 3 - Evolution Notes
Evolution involves change over time....from a biology standpoint evolution looks at how organisms change over long periods of time over many generations and hundreds of thousands of years.

Source of Genetic Change

Mutations are the source of genetic change * Neutral mutations - do not seem to benefit or harm the organism * Harmful mutations - negatively affect the life of organisms * Beneficial mutations - positively affect the life of organisms

Artificial Selection

Many species of plant and animal have been domesticated meaning that humans bring them into their homes or near to where they live. Humans have been involved in selecting traits that are desirable and only breeding those plants or animals with desirable traits into future generations.

Ex - Wolves have been domesticated into many different breeds of dog
Wild Sea Cabbage has been bred into brussel sprouts, cabbage, cauliflower and broccoli!

Proof

Dimitri Belyaev - did an experiment with the silver and red fox. He selected only foxes that have the trait of being tame. After 35 generations (within his lifetime), he was able to breed tameness into 80% of the offspring. They became very dog like and even changed appearance to be more dog like.

Problems with artificial selection * Breeders may favour traits that lead to less genetic diversity * Some dogs have bad hips * Sweet corn is prone to insect damage

Leading to Evolution * French scientist – Buffon wondered about anatomical features that served no purpose * Life must change over time he thought (from perfect to different)...not true but interesting

* Lamarck proposed two principles * Use and it gets stronger, disuse and it gets weaker (ex...Giraffes stretch their necks to get food...their necks get longer) * The inheritance of acquired characteristics (ex...future generations of Giraffes pass along their longer necks to offspring)...this is not true but does lead to thinking about evolution
Evidence of Change in Fossils
Fossils are loosely defined as being over ten thousand years or older
Reading Fossils * Many fossils appear to be of unusual and unknown organisms...thousands of species are no longer living * No fossils or most living species * Fossils are deep within rock formations...some 1 km below Earth’s surface * Fossils are found in unexpected locations...sea life in mountains and deserts? * continued * Fossils of simple organisms are found in all depths * Fossils of more complex organisms are only at shallow depths * Fossils at shallow depths more likely resemble living species * Rock layers contain fossils of many species that do not occur in layers above or below them

Uniformitarianism

* Charles Lyell – father of Modern Geology * Earth has been changed by the same processes in the past that are occuring in the present * Geological change is slow and gradual rather than fast and catastrophic * Natural laws that influence these changes are constant and eternal, and they operated in the past with the same intensity as they do today * EARTH IS EXTREMELY OLD and LIFE HAD A LONG TIME TO EVOLVE ...this was radical thinking back in 1830!!

The Origin of Species (1859)
There are two main points that Charles Darwin had to his theory on the Origin of the Species

1. Common Descent * descent with modification * all organisms related through descent from some unknown prototype that lived in the remote past * habitat influence accumulation of adaptations for specific ways of life

2. Natural Selection and Adaptation

Signs Of Evolution
Biogeography
* geographical distribution of species
Fossil Record * succession of forms
Taxonomy
* descent from common ancestors
Comparative Anatomy
Homologous versus Analogous features * homologous - structures share a common origin but serve different functions in modern species * analogous - structures similar in function but not in origin
Vestigial features * features that have lost their function or have minimal function
Comparative Embryology * features in developing embryos across many different species are similar
Molecular Biology * Evolutionary relationships among species are reflected in DNA and proteins * genetic distance between species can be compared * mtDNA - mitochondrial DNA can also be compared

Modern Evolutionary Theory * Darwin’s theory of natural selection explained how evolution happened * Success means producing offspring and passing along your genes...if you survived, whatever traits you possessed to help you survive get passed on * Modern Evolutionary Synthesis combines Darwin’s Natural Selection with gene variation through the generations

Sexual Variation – Not a mutation

Sexual reproduction produces variations because of crossing over and random assortment of chromosomes....this produces slight variations in a species and potentially some will be more successful that others

Mutations

* Recall that base pairs can be substituted during DNA replication * Crossing over can have mutations if alleles are misaligned * Genes can get duplicated during meiosis which leads to more than one copy of a gene which can be beneficial * The extra gene can mutate leading a new traits or protein synthesis * If the mutation is beneficial, nature selects for that and that species becomes more successful

Mutation Rates

* If your genome is large, you have a greater chance for mutations to occur. In humans, we think that about 20 mutations occur in your 3 billion base pairs. * That is per person so on the planet, there are well over 100 billion mutations present

Homologous Genes

* Since mammals have a common ancestor, you would expect homologous genes to be similar.

Psuedogenes

* Genes that have undergone mutations and do not serve a useful purpose anymore * Following the psuedogenes can help link species together to following their evolutionary changes

Types of Natural Selection * Directional Selection * Individual has a more extreme variation of the trait * Results in a shift away from the average condition * Stabilizing Selection * Average phenotype is favoured * Disruptive Selection * Favours two individual traits at opposite extremes of phenotype because environmental conditions are at two different extreme * Sexual Selection * Favouring of any trait that enhances mating success * Leads to female mate choice...appearance of males is attractive...mating rituals * Leads to male to male competition * Males that mate many females pass along their part of the genetic information to many offspring...and biologically that is successful

Selection Due to Genetic Factors

Note that these factors do not rely on natural selection

* Genetic Drift * The random shifts of genetic makeup of the next generation from changes in allele frequency by chance * The smaller the population is, the greater the influence * Bottlenecks * Genetic bottlenecks result in the loss of genetic diversity following an extreme reduction in population * With the reduction in population comes a reduction in the number of allele variations found * If the population recovers, only those alleles (and any mutations) move forward into the offspring * Cheetahs have little genetic variability...it is thought that only seven individuals survived a bottleneck event 10000 years ago. * Founder Effect * A type of genetic drift that results when a small number of individuals separate from their original population and establish a new population * The types of alleles that are in the small population can be significantly different or rare by chance * If the population is very small, then you start with a new gene pool which is very different from the original population

Hardy-Weinberg Principle

* In large populations in which only random chance is at work, allele frequencies are expected to remain constant from generation to generation * Changing allele frequency leads to evolutionary change

Hardy-Weinberg principle leads to the following conditions for evolution to occur * Natural selection * certain alleles get passed on as a result of a species suited to a particular environment * Small population size * the smaller the population, the more genetic drift can occur * Mutation * random mutations introduce new types of alleles or removes alleles because genes stop functioning properly * Immigration or Emigration * new alleles appear in populations due new species moving into an area * Horizontal gene transfer * new alleles from different species are transferred into a genome

There are other considerations * Need to consider biology of species * Reproductive Biology (how long to make offspring) * Genetic diversity * Example – species with short reproduction times and high genetic diversity respond to natural selection rapidly...insect become pesticide resistant

Humans have drastically altered environments and ecosystems by any of the following: * commercial fishing * habitat loss * climate change * selective hunting * chemical pressures from insecticides, herbicides, fungicides * antibiotic and antimicrobial

Speciation

* Speciation is the formation of a new species * A species is not an easy thing to define * Includes all the members of a populations that can interbreed under normal conditions

Modes of Speciation

* Reproductive isolation * When a species evolves such that it is isolated from breeding and must establish a new interbreeding population * Evolution can involve differences in: * breeding season * physical traits * behavioural traits * habitat preferences * incompatible genes

Reproductive isolation can be prezygotic (happening before the zygote is formed) or poszygotic (happening after the zygote has formed)

* Allopatric Speciation occurs when evolutionary changes happen following a period of geographic isolation

* Sympatric Speciation – evolution of populations within the same geographic area into separate species by becoming genetically isolated * For example: a mutation can cause polyploidy or doubling of the original number of chromosomes. Polyploids can mate with each other to produce normal offspring while polyploids mating with diploids will produce infertile offspring...hence genetic isolation

Different Forms of Evolution

* Adaptive Radiation * Rapid evolution of a single species into many new species which fill a formerly empty ecological niche (example Darwin’s finches)

* Divergent Evolution * The large scale evolution of a group into many different forms due to the abundance of particular niches (example the variety of rodents) * This form of evolution minimizes competition and increases biodiversity

* Convergent Evolution * Two species placed under similar selective pressure will co-evolve to two produce two different species to occupy similar * This form of evolution favours similar traits in similar environments

* Convergent Evolution * Two species placed under similar selective pressure will co-evolve to two produce two different species to occupy similar * This form of evolution favours similar traits in similar environments

Looking at Large Scale Evolution - Macroevolution

Looking at Earth's history, we see evidence of many mass extinctions followed by significant increases in biodiversity.

The dinosaur extinction is theorized to be due to a massive asteroid impact 65 million years ago

Look at how to do Cladistics which show evolutionary relationships of different groups of species of living things

Changes can happen gradually or quickly

* Theory of gradualism – new species evolve and appear similar to the original species....the changes occur slowly * Theory of punctuated equilibrium – evolution is slow but occasionally occurs very quickly and then goes back to being slow...causes a problem for fossil record * BOTH OCCUR!

The Missing Link

* Can’t find a transitional fossil...must be because evolution is wrong! * Can’t find the element technetium in nature....periodic table must be wrong! * NOT SO...we found technetium * We found several missing links....archaeopteryx ...has features of bird and reptiles...birds and reptiles are in the same class

Human Evolution

* Homo sapiens (today’s humans) are primates and more specifically hominids * There is a common ancestor of primates about 60 to 70 million years ago * Human and chimpanzee DNA is 98.8% similar * Human and gorilla DNA is 98.4% the same

Out of Africa

* All early hominids lived in Africa * Homo erectus left Africa and went to Eurasia (1.9 million years ago but died out 100 000 years ago) * Homo neanderthalenis parts of Europe about 300 000 years ago * Soon after that, modern humans evolved