Evolution: Natural Selection and Genetic Variation

• The theory of evolution states that the diverse plant, animal, and other living forms on Earth originated from pre-existing types through modifications across generations.
• Biological evolution is descent with modification, where organism lineages change over generations, leading to diversity as lineages from common ancestors diverge over time.
• Charles Darwin proposed biological evolution by natural selection, where organisms with heritable traits that favor survival and reproduction leave more offspring, increasing the trait frequency across generations.
• Evolution is change in the heritable characteristics of biological populations across generations.
• These characteristics, expressions of genes passed from parent to offspring during reproduction, vary within populations due to mutation, genetic recombination, and other sources of genetic variation.
• Evolution occurs when processes like natural and sexual selection or genetic drift act on this variation, changing the prevalence of specific characteristics in a population.
• Patterns of biodiversity have been formed by the repeated emergence of new species (speciation), changes within species (anagenesis), and species loss (extinction).
• Species with more recent common ancestors exhibit greater similarity in morphological and biochemical traits.
• Morphological and biochemical traits can reconstruct phylogenetic trees, showing evolutionary relationships between species.
• In the 1850s, Charles Darwin wrote "Origin of Species," that proposed species evolved through "descent with modification" from a common ancestor.

Evidence of Evolution

• Evolution is a key principle in biology.
• Evolution is a change in the genetic makeup of a population over time
• Anatomy shows certain anatomical features of vertebrates are evidence for evolution.
• Fish have a simple heart with one auricle and one ventricle.
• Amphibians have one ventricle and two auricles.
• Reptiles have two auricle and one partially divided ventricle.
• Birds and mammals have two auricles and two ventricles.
• Also a change from single to double circulation of blood in animals.
• Homologous features such as complex bone structures or body plans indicate shared ancestry.
• The similar bone structure in the forelimbs of whales, humans, birds, and dogs suggests a common ancestor.
• Analogous features are physical similarities in different organisms that evolved independently due to organisms living in similar environment of experiencing similar selective pressures.
• Arctic fox and ptarmigan undergo seasonal color changes which does not reflect common ancestry.
• Bird and bat wings are used for flight and look superficially similar, are constructed in different ways and are analogous structures that evolved independently.
• Embryos of vertebrates have gill slits and a tail during development.
• Shared features suggest living things are descended from a common ancestor with DNA as its genetic material, used in transcription and translation.
• Homologous or orthologous genes in different species are compared to determine their evolutionary relationship.
• Humans and chimpanzees insulin proteins are more similar than human and chicken insulin proteins.
• Geographic distribution of organisms and unique groups of plants and animals on northern and southern continents can be traced to the split of Pangaea into Laurasia and Gondwana.
• Most mammal species in Australia are marsupials, while elsewhere they are placental, which led to the isolation for millions of years.
• Fossils show that different organisms have lived on Earth during different periods.
• Fossils of horses have allowed scientists to reconstruct a branching "family tree" for horses and their now-extinct relatives.
• Fossils are mainly found in sedimentary rocks.
• Annelid fossils appear very early while fossils of reptiles appear late in geological records.
• Bone, teeth, shells and woody parts of plants that are found petrified, are also fossil evidence.
• Examples of the evolution taking place is development of drug-resistant bacteria and pesticide-resistant insects.
• DDT resistance in mosquito populations was observed directly in the 1950s.
• Mosquito populations evolved resistance due to natural selection.
• Industrial melanism is the spread of 'industrial melanin' a dramatic darkening in colouration in regions of heavy industrialization in Britain.
• Biston betularia, the peppered moth assumes a dark colour, preventing it from being preyed on by birds.
• Organisms have structures that serve no apparent function but are homologous to useful structures in other oganisms which are called vestigial structures.
• Examples of vestigal structures are the tailbone of humans, the hind leg bones of whales, and the underdeveloped legs found in some snakes.
• Biochemists have found similarity of the chemical composition of all protoplasm.
• All plant and animal cells carry out metabolic activities.
• Proteins in closely related organisms have very similar amino acid sequences.
• Most vertebrates share the same of similar hormones.
• In vertebrates, all red blood corpuscles contain haemoglobin.
• The geological time table is a method of relating the timing and relationship between events that have occurred during the history of the Earth.
• The Earth is more than 4.5 billion years and life on Earth originated about 2 billion years ago.
• Neo-Darwinism is also called the modern evolutionary synthesis or modern synthesis, incorporates Charles Darwin's theory of evolution by natural selection and Gregor Mendel's theory of genetics as the basis for biological inheritance.
• The modern synthesis integrated scientific disciplines and theories into a common view of evolution can be explained by small genetic changes in populations over time, due to natural selection.
• The modern synthesis connected natural selection and population genetics, based on Mendelian inheritance.
• A major conclusion of the modern synthesis is that populations can explain evolutionary changes, consistent with the observation of naturalists and genetic mechanisms.
• Darwinism declares that all species of organisms arise and develop through that natural selection of small, interited variations that increase indvidual's ability to compete, survive, and reproduce.
• Darwin's general theory presumes the development of life from non-life and stresses the naturalistic "descent with modification".

Darwin's Theory of Evolution by Natural Selection

• Evolution by natural selection is the process where traits enhancing survival and reproduction become common over generations.
• Traits are often heritable, passed from parent to offspring.
• Organisms produce more offspring than the environment can support, leading to competition for resources.
• Offspring vary in heritable traits such as color, size, shape, etc.
• Darwin concluded the following
• Some individuals will have inherited traits that help them survive and reproduce.
• Helpful traits are heritable so it will become present in more of the next generation.
• Over generations, the population will adapt to its environment as individuals with traits helpful in that given environment can survive and reproduce.
• Darwin reasoned that there must be variations in nature that were favorable or useful to the organism in the struggle for existence.
• Favourable variations are ones that increase chances for survival and procreation.
• The outcome is an organism to survival in it's environment where evolution will occurs as a consequence.
• Natural selection preserves and accumulates minor advantageous genetic mutations or variations.
• Breeders eliminate undesirable traits gradually over time.
• Selection may occur because of survival, fertility, rate of development, and mating success.
• The evolutionary fitness of an organism also called darwinian or relative fitness.
• Fitness is measured by an organism's ability to survive and reproduce.

Competition for Resources

• Competition is the interaction among organisms of the same or different species associated with the need for a common resource, like food, space, water, and light, etc. in a limited supply relative to demand.
• Is an interaction between organisms or species in which both organisms or species are harmed.
• Competition is one of many interacting biotic and abiotic factors that affect community structure.
• Competition amoung members of the same species is known as intraspecific competition, while amoung members of different species is known as interspecific competition.
• Interference competition occurs directly between individuals via aggression when the individuals interfere with foraging, survival, reproduction of others or directly preventing their physical establishment in a habitat.
• Exploitative competition occurs when individuals interaction indirectly as they compete for common limiting resources, like territory, prey or food.
• Apparent competition occurs when two individuals that do not directly compete for resources affect each other indirectly by being prey for the same predator.
• Competition can cause species to evolve differences in traits because the individuals of a species with traits similar to competing species always experience strong interspecific competition.
• Therefore, whenever populations of a species are crowded, intraspecific competition is intense.
• Intraspecific competition can be a selective factor in evolution.
• The competitive exclusion principle which states that species with ecologically identical life styles and resource needs cannot coexist over the long term; the competitively less-fit species will be displaced by the better fit species.
• Such variations, because they are not genetically acquired but environmentally acquired or influenced characters, cannot be inherited by the offspring.
• Genetic variation: This refers to differences amongst organisms of the same species due to the differences in the genes they inherit from their parents.
• Example: Some individuals are tall and others are short. There are two types of genetic variation.
• Continuous variation
• Discontinuous variation
• Continuous or quantitative variation is where differences among organisms of the same species are slight and grade into each other.
• Discontinuous Qualitative Variation is the variation that shows clear-cut and sharp differences amongst organisms over a given trait.
• There are mainly two causes of variation
• Environmental factors
• Genetic factors
• Survival of the fittest refers to the organism or species that is best suited for the immediate, local environment where its defined as reproductive success (natural selection).
• Individuals who have the favorable adaptations will live long enough to pass down those genes to their offspring.
• Mutations is any change in the DNA sequence of an organism.
• Mutagens are any agent that can increase the rate of mutation.
• DNA is made of units, A (adenine), T (thymine), G (guanine), and C (cytosine).
• Types of Mutations
• Substitution
• Insertion
• Deletion
• Frameshift causes DNA codons to parsed incorrectly resulting in truncated proteins.
• DNA fails to copy accurately.
• External influences can create mutations such as radiation cause the DNA to break down.
• Mutations can also be deleterious or beneficial.
• Mutations are essential to evolution.
• New genetic variant (allele) spreads via reproduction where differential reproduction is a defining aspect of evolution.

Adaptations to the Enviroment

• Adaptations can be a behavior, a protein, or an anatomical feature.
• Organisms show adaptive plasticity as traits develop in response to environmental challenges.
• Adaptive radiation is a process in which organisms diversify rapidly into a multitude of new forms, particularly when a change in the environment.
• The most common example of adaptive radiation is finch speciation on the Galapagos known as Darwin's finches.
• Adaptive radiation can identified by the following four features or characteristics:
• A common ancestry of component species.
• A phenotype-environment correlation.
• Trait utility.
• Rapid speciation.
• Following are conditions that permit the occurrence of adaptive radiation:
• A new habitat has opened up.
• This new habitat is relatively isolated.
• The new habitat needs a wide availability of niche space.

Isolating mechanisms

• Reproductive isolating mechanisms or isolating mechanism are the biological properties of organisms that can prevent interbreeding or reduce/prevent successful reproduction.
• Types of Isolating Mechanisms
• Prezygotic or Pre-mating
• Ecological isolation: Individuals mate in their preferred habitat.
• Temporal isolation: Individuals of different species do not mate because they are active at different times of day or in different seasons.
• Ethological or behavioral isolation: Potential mates meet, but choose members of their own species.
• Mechanical isolation: Copulation is attempted, but transfer of sperm does not take place.
• Postzygotic or Post-mating: reduced in viability or fertility.

The Origin of Life-

Theories to explain the origin of life

• Theory of Special Creation - Life was created by God.
• Theory of Spontaneous Generation - Life arose spontaneously from non-living matter.
• e.g., Horse hair in water create horsehair worm, meat creates fly larvae.
• Theory of Catastrophism - God created life and catastrophies occurred afterward.
• Theory of Cosmozoic - Life formed in different planet as spores and arrived on Earth.
• Theory of Eternity of Life - Life has no end or beginning
• Modern Theory, a.k.a. Chemical Theory - Life can arise spontaneously if inorganic molecules react with each under the right conditions (solar energy, ultraviolet raditation). There are 355 genes from the last universal common ancestor.

Fossils and Human Evolution

• Human evolution starts with the appearance of the first mammals on Earth.
• In the Jurassic period mammals appeared on Earth which were stemmed from the cotylosaurs or stem reptiles.
• The primates appeared about 65 million years from the shrew link small insectivores.
• These mammals have acquired 5 important features to maintain tree life.
• Bipedal locomotion
• Grasping hand and feet
• Stereoscopic vision
• Reduction in snout
• Enlargement of brain
• The evolutionary line of monkey and apes has several stages
• Parapithecus - Earliest fossil form of monkey, ape and man
• Propliopithecus - Evolution from these yield gibbons
• Dryopithecus - Considereed fossil ape and a common ancestor of the great ape
• Proconsul - Evolved from Dryopithecines
• Human Ancestral Forms
• Ramapithecus - Lived on trees and ate on the ground.
• Australopithecus - First Ape-man
• Homo habilis - Usage of tools were beginning and has closure man-like
• Homo erectus - Making fine quality tools, know of fire and erect posture
• Homo neanderthalensis
• Made tools, used animal hides, knew of fire, and perform rituals
• Homo sapiens (or modern man)
• This has made him the most domina