Comprehensive Notes on the Theory of Evolution
Chapter 12: Theory of Evolution
12-1 The Work of Charles Darwin
Darwin's Journey:
Charles Darwin, though not initially a stellar student, became a pivotal figure in science.
He was appointed as an unpaid naturalist on the HMS Beagle voyage.
The ship's primary mission was to chart the South American coastline.
Darwin's acceptance of the role was initially opposed by his father but later supported by his uncle.
Initial Beliefs:
Darwin initially believed in the prevailing view of species as divinely created, unchanging entities.
Shifting Perspectives:
Fossil discoveries challenged the traditional view of divine creation.
Jean Baptiste Lamarck:
Proposed a mechanism for evolution (later proven incorrect).
His hypothesis involved the inheritance of acquired characteristics.
Example: Giraffes evolving longer necks by stretching, with this trait passed to offspring (Figure 12-3).
Observations on the Beagle:
Darwin read Charles Lyell's "Principles of Geology," which discussed Lamarck's theory.
He observed similarities and differences between fossils and living species in South America, suggesting evolution.
The Galapagos Islands provided key evidence: plants and animals resembled those of the South American coast.
Darwin reasoned that species migrated from South America to the Galapagos and then evolved.
He termed this change "descent with modification," which is evolution.
Darwin Seeks Explanation:
Darwin continued studying plants and animals after returning from the voyage.
He married, had 10 children, and meticulously analyzed his collected specimens.
He sought a mechanism to explain how evolution occurs.
Malthus's Influence:
Thomas Malthus's Essay:
Stated populations could increase faster than the food supply.
Population grows geometrically, while food supply grows arithmetically (Figure 12-5).
Malthus argued unchecked population growth would lead to resource scarcity, but this is prevented by factors like disease, war, and famine.
Population Definition:
A group of individuals of the same species living in a defined area and interbreeding.
Natural Selection:
Darwin applied Malthus's principle to all species: organisms produce many offspring, but only a limited number survive to reproduce.
Key Realization:
Individuals with superior traits are more likely to survive and reproduce, passing favorable characteristics to offspring.
This process, where populations change in response to their environment, is called natural selection.
Evolution by natural selection explains biological diversity.
Adaptation occurs as species evolve in response to their environment.
Darwin noted species in nearby geographic locations are more similar than those in similar, distant areas, implying evolution from common ancestors.
Publication Delay:
In 1844, Darwin documented his ideas but hesitated to publish due to public criticism of evolution-related books.
He continued refining his notes for 14 years.
The Wallace Letter:
Alfred Russel Wallace sent Darwin an essay describing evolution by natural selection.
This prompted Darwin to publish his work alongside Wallace's.
Both papers were presented at a scientific meeting in 1858.
On the Origin of Species:
Darwin's book was published in 1859 and caused a sensation (Figure 12-6).
It presented evidence for evolution and a mechanism for how it occurs.
His ideas were widely accepted by biologists despite some public reservations.
Updated Ideas:
Darwin's hypothesis of natural selection has been examined and updated with new genetic discoveries.
Key Points:
Individuals best suited to their environment leave the most offspring, making their traits more common.
Genes are responsible for inherited traits.
Natural selection causes gene frequencies in a population to change over time.
Microevolution:
Change within a species over time (Figure 12-7).
Mutations and genetic recombination provide new variations.
Isolation leads to divergence- different environments will evolve differently.
Speciation:
Isolated populations may become unable to interbreed, leading to new species formation.
Macroevolution:
Extinction of some species allows better-suited species to replace them.
Replacement of dinosaurs by mammals is an example.
12-2 Evidence of Macroevolution
Three Major Points:
Earth is approximately billion years old.
Organisms have inhabited Earth for most of that time.
All organisms evolved from earlier, simpler life forms.
Fossils:
Provide direct evidence of macroevolution.
They are preserved remains or traces of ancient organisms.
The fossil record shows change over time, with older rocks containing different fossils than newer rocks (Figure 12-8).
Fossil links have been discovered between major groups of organisms like fish and amphibians.
Fossilized remains of whale ancestors provide links to four-legged land mammals (Figure 12-9).
*Fossil Formation:
*Organisms that are rapidly buried in fine sediments deposited by water, wind, or volcanos are more likely to become fossilize (e.g., wet lowlands, slow-moving streams, lakes, shallow seas, and areas near volcanoes that spew).
Limitations of the Fossil Record:
The fossil record is incomplete.
Many species lived in environments where fossils don't form.
Fossil formation requires rapid burial in sediment, which doesn't always happen.
Radiometric Dating:
Paleontologists use radiometric dating to determine the age of fossils.
This allows them to arrange fossils in sequence.
Family trees diagrams shows how organisms are related through evolution (Figure 12-10).
Molecular Record:
Changes in genes should accompany species evolution.
Nucleotide sequence changes accumulate over time.
Species that diverged long ago should have more differences in protein amino acid sequences.
Hemoglobin Comparison:
Comparison of the beta chain of human hemoglobin with that of several species reveals these differences (Table 12-1).
*Human vs. Gorilla=few amino acid sequence differences since they recently shared a common ancestor.
*Human vs. Frog=many amino acid sequence differences since they shared a common ancestor in the distant past.
Scientists estimate nucleotide substitutions by counting amino acid sequence differences.
Gene sequencing helps determine the exact nucleotide sequence of genes.
Family trees are constructed using molecular data, supporting the fossil record (Figure 12-11).
Anatomy and Development:
Homologous Structures:
Anatomical comparisons reveal basic similarities in body structures, even with different functions.
Vertebrate forelimbs have the same basic bones used for different purposes (Figure 12-12).
These structures share a common ancestry.
Vestigial Structures:
Reduced structures with no or less prominent function.
Evidence of an organism's evolutionary past.
Example: The flightless cormorant's wings (Figure 12-13).
The human coccyx is another vestigial structure.
Embryonic Development:
Vertebrate embryos show similarities early in development (Figure 12-14).
Each has a tail, limb buds, and pharyngeal pouches.
These disappear in humans by birth.
These similarities suggest that vertebrate development evolved by layering new genetic instructions on older ones.
Rate of Evolution:
Gradualism:
Evolution as a gradual process over long periods.
Punctuated Equilibrium:
Evolution occurs in spurts separated by long periods of stability.
Major environmental changes impact species formation.
These changes can be linked to volcanic eruptions, asteroid impacts, and ice ages.
Such changes create opportunities for colonization by rapidly adapting species.
*Gradualism vs Punctuated Equilibrium (Figure 12-15).
*The fossil record seems to provide evidence of both types of evolution.
12-3 Evidence of Microevolution
Natural Selection:
Is the primary mechanism responsible for evolution.
Five Main Elements:
Genetic variation exists within species.
The environment poses challenges to survival.
Organisms produce more offspring than the environment can support, leading to competition (struggle for survival).
Individuals better suited to the environment leave more offspring (survival of the fittest).
Favorable characteristics increase in a population over time.
The environment dictates the direction and extent of change (Figure 12-16).
Industrial Melanism:
Example: The European peppered moth, Biston betularia.
Darkening of populations in response to industrial pollution.
Dark moths became more common in industrialized areas after 1850.
Concealment Hypothesis:
Dark moths are camouflaged against soot-darkened bark, avoiding bird predation.
Kettlewell's Experiment:
H.B.D. Kettlewell released marked light and dark moths in polluted and unpolluted areas.
Observed differential Moth Survival (Figure 12-17).
* More moths matching the tree color survived.
* Natural selection causes industrial melanism.Sickle Cell Anemia:
Hereditary disease affecting hemoglobin molecules.
Caused by a single nucleotide change in the beta-hemoglobin gene.
Sickled red blood cells clog arteries, often leading to death.
Heterozygous individuals have enough functional hemoglobin to remain healthy.
The sickle cell allele is common in central Africa (Figure 12-18).
Malaria Resistance:
Heterozygous individuals are more resistant to malaria.
Distribution of Sickle Cell Allele, closely coincides with malaria (Figure 12-18). * Even though homozygous individuals with sickle cell anemia die, the population experiences fewer malaria-related deaths.
Balancing Selection:
Natural selection acts in opposing ways (elimination vs. preservation).
Maintains both normal and sickle cell alleles in the population.
Directional Selection:
In areas without malaria, the sickle cell allele is being eliminated since there is no balancing advantage.
The environment determines the direction of evolutionary change.
Species Formation:
Ecological Races:
Local populations adapt to different environments, becoming distinct.
Example: Seaside sparrows (Figure 12-19).
These races may continue to diverge and eventually become separate species.
Reproductive Isolation:
Prevents interbreeding between closely related species.
Barriers to reproduction maintain new species.
Examples: behavioral, temporal, and ecological isolation (Figure 12-20, Table 12-2).
Speciation Summary:
Begins with population adaptation.
Reproductive isolation prevents interbreeding.
Microevolution to Macroevolution:
Microevolution leads to new species and kingdoms.
Observed stages of speciation are well-documented.
Changes accumulate over time, leading to significant differences from ancestors.