Evolution and Natural Selection

Evolution Overview

• Evolution happens via species transformation over time, leading to a wide variety of life.
• The main mechanisms are variation, natural selection, inheritance, and genetic drift.
• These mechanisms act on populations, enabling adaptation and evolution into new species over long periods.

Variation

• A key element of evolution.
• Populations consist of non-identical individuals differing in physical traits, behavior, and genes.
• Differences arise from mutations, random DNA changes, genetic recombination, and environmental pressures.
• Some variations are beneficial for survival and reproduction.
• Other variations are neutral or detrimental.
• Evolution requires genetic variation.

Natural Selection

• The main driving force behind evolution.
• Organisms with advantageous characteristics (e.g., camouflage, speed, immunity) are more likely to survive and reproduce.
• Advantageous characteristics become more common, while less beneficial ones are lost.
• Species become better adapted to their environments.

Inheritance

• Characteristics must be passed to offspring for evolution to occur.
• Genes, parts of DNA, provide directions for these characteristics.
• Genetic information is transferred during reproduction.
• Evolutionary adjustments accumulate over time.

Genetic Drift

• Evolution occurs by chance, unlike natural selection.
• Random events alter a population's genetic composition.
• A disaster could kill off part of a population, leaving only a few individuals to breed.
• Traits of the remaining individuals become more prevalent, even without a survival advantage.
• Genetic drift is more powerful in small populations, where random alterations impact genetic diversity.

Speciation

• Evolution over long periods can result in new species.
• Occurs when populations become geographically or behaviorally isolated.
• Genetic differences accumulate until interbreeding is no longer possible.

Evolution Significance

• Evolution is a continuous process that has shaped life for billions of years.
• All species, including humans, have evolved through basic mechanisms.
• Knowledge of evolution provides insights into biology, medicine, and Earth's future.

Theories of Evolution

• Influenced by multiple scientific theories describing species evolution.
• The most famous theory is Charles Darwin's natural selection.
• Other theories include Lamarck's acquired characteristics, Darwin's natural selection, mutation theory, and modern evolutionary synthesis.

Lamarck's Theory

• Proposed by Jean-Baptiste Lamarck in the early 19th century.
• Organisms modify themselves during their lifetimes based on needs.
• Acquired characteristics are passed to descendants.
• Example: Giraffes evolve longer necks by stretching.
• Offspring inherit this characteristic.
• Refuted as genetic alterations do not occur through acquired traits, rather through mutations and natural selection.

Darwin's Theory

• Natural selection theory presented in "On the Origin of Species" (1859).
• Individuals within a population differ in characteristics.
• Beneficial characteristics lead to survival and reproduction.
• Favorable characteristics become more prevalent over time.
• Species change gradually through inherited genetic characteristics.

Mutation Theory

• Proposed by Hugo de Vries
• Sudden genetic changes, or mutations, create new traits in organisms.
• Mutations providing a survival advantage spread through a population.
• Mutations contribute to genetic variation on which natural selection acts.

Modern Synthesis of Evolution

• Formulated in the 20th century.
• Unites Darwin's natural selection with Mendelian genetics.
• Evolution is caused by genetic mutations, recombination, gene flow, and genetic drift.
• Explains how inheritance occurs.
• Populations change with gradual changes and genetic variations over time.
• All theories contribute to our understanding of evolution.
• Darwin's theory is the basis of modern evolutionary biology.
• Mutation theory and modern synthesis explain genetic processes of evolution, which create a complete picture of how life developed .

Evidence for Evolution

• Supported by scientific evidence from biology and geology.
• Evidence collected from fossils, comparative anatomy, embryology, molecular biology, and biogeography.
• All show species have evolved over time and share common ancestors.

Fossil Record

• Strongest evidence for evolution.
• Fossils are remains/traces of ancient organisms preserved in rock layers.
• Fossils reveal how species evolved over millions of years.
• Transitional fossils (e.g., Archaeopteryx) show traits of reptiles and birds.
• Fossils of early hominins illustrate human evolution from ape-like ancestors.

Comparative Anatomy

• Illustrates structural homology among species.
• Homologous structures (e.g., human forelimb, bat forelimb, whale forelimb, bird forelimb) have varied uses but similar skeletal makeup.
• Reflects common ancestry.
• Analogous structures (e.g., wings of birds and insects) do similar work but developed differently.
• Illustrates convergent evolution.

Embryology

• Science of embryos in development.
• Vertebrate embryos (fish, birds, mammals) resemble each other in early development.
• Suggests a common ancestor.
• Structures like gill slits and tails in human embryos indicate connections with aquatic ancestors.

Molecular Biology

• Provides strong evidence for evolution.
• DNA comparisons reveal genetic similarities between species.
• Humans share 98% of DNA with chimpanzees.
• Vestigial genes (e.g., for producing vitamin C in primates) are functional in some species but inactive in others.
• Confirms evolutionary relationships.

Biogeography

• Species distribution.
• Distinct fauna of remote islands (e.g., Galápagos finches) shows how species evolve based on surroundings.
• Similar species in nearby areas indicate evolution from a common source.
• Fossils give a record of the past.
• Anatomy and embryology shows structural and developmental homologies.
• Molecular biology verifies genetic affinities.
• Biogeography accounts for species distribution.
• All prove life on our planet has evolved through natural mechanisms.

Theories of Evolution

• Descent with modification asserts that all living things share a common ancestor.
• They develop over time through inherited changes.
• Evolutionary theory and diversity of life rely on this concept.
• Charles Darwin's natural selection is the most prominent and accepted theory of evolution.
• Evolutionary thinking has changed, incorporating new scientific findings.

Descent with Modification

• Organisms transmit genetic characteristics to offspring with slight differences during reproduction.
• Advantageous differences aid survival and reproduction.
• Useful characteristics become more prevalent over generations.
• Less beneficial characteristics disappear.
• Incremental processes result in new species.
• Fossil evidence, comparative anatomy, and genetics support this idea.
• Fossil demonstrates evolution over millions of years.
• Anatomical and DNA similarities verify common descent.

Early Evolutionary Accounts

• Early accounts of evolution were often misleading.
• Jean-Baptiste Lamarck thought organisms could gain traits during life.
• Traits would then be transferred to offspring.
• Giraffes evolving long necks by stretching to reach leaves was an example.
• Was proven incorrect.
• Traits gained in life are not inherited genetically.
• Darwin's natural selection gives a better explanation.

Darwin's Natural Selection

• Organisms with favorable characteristics have a better chance of passing them on
• Can result in species changing gradually over time.
• The range of finches located throughout the Galapagos Islands, display adequate changes as a result of their individual food source
• Unlike Lamarck, Darwin was confident that evolution occurred via inherited hereditary variations and not through acquired traits

Modern Synthesis

• Darwin's natural selection was synthesized with Mendelian genetics in the 20th century.
• This gives a greater understanding of evolution.
• Mutations in DNA form genetic variation, which is acted upon by natural selection.
• A finding that further reinforced the theory of evolution.
• Today, evolutionary theory continues to evolve with breakthroughs in genetics, molecular biology, and paleontology.
• DNA sequencing, in conjunction with the discovery of certain fossils, is employed by scientists to track evolutionary patterns.
• Descent with modification is a core concept.

Systematics Defined

• Classifies organisms and establishes evolutionary relationships.
• Rooted in evolutionary ideas, specifically descent with modification.
• Traces evolutionary lineages, appreciates biodiversity, and classifies life into categories.

Systematics Characteristics

• Systematics combines taxonomy, phylogenetics, and molecular biology.
• Taxonomy, the study of naming and classifying living things, is the foundation of systematics.
• Carl Linnaeus created the binomial nomenclature system (two-word Latin name) for each species.
• Evolutionary theory transformed taxonomy.
• It expresses common ancestry.

Taxonomy

• Taxonomists organize organisms into hierarchical categories (domain, kingdom, phylum, class, order, family, genus, species).
• Based on evolutionary relationships.
• Diagrams that depict how species have descended from common ancestors are called Phylogenetic trees .
• Scientists use fossil remains, comparative anatomy, and molecular information to construct these trees.
• Genetic similarities in DNA sequences, show specific aspects of evolutionary relationships.
• Molecular biology enables scientists to compare genetic information across species.
• Research has revealed that humans and chimpanzees share nearly 98% of their DNA.
• Molecular clocks approximate the time of divergence between species.

Systematics Applications

• Can be applied beyond classification; for example everyday applications in medicine, conservation, and ecology.
• Evolutionary relationships aids scientists in discovering potential new medicines, following the transmission of diseases, and plan conservation programs for threatened species.
• By analyzing systematics help conserve biodiversity.
• Researchers can predict how species are likely to adapt to environmental changes.
• Offers a classification system to understand life.
• Can improve classifications.
• Provides information about the relationships between species.
• Further establishes the influence of evolution on the diversity of life.