Chapter 22: Darwin and Descent with Modification
NOTE: ONLY HAS LECTURE INFO NOT TEXTBOOK
Myth Busting
evolution is a theory about the origin of life
false, evolution is a theory about how life has changed over time
abiogenesis is the leading scientific hypothesis about the process from which life arose on earth
transition from dead to living planet was not a single step
earth has a reducing atmoshpere for natural molecules to exist
abiotic (nonliving) synthesis of small organic molecules, such as amino acids and nitrogenous bases
these small molecules join into macromolecules, such as proteins and nucleic acids
these molecules get packed into protocells (droplets with membranes that maintained an internal chemistry different from that of their surroundings)
the origin of these self-replicating molecules eventually made inheritance possible
evolution is like a clumb up ladder of progress, organisms are always getting better
“better” is linked to the environment, not to progress
organisms change to adapt to the environment
many taxa (mosses, fungi, corals, crayfish) have changed little over significant expanses of time
ex. stromatolites have existed for over 3.5 billion years as basic, single-celled organisms
evolution means that life changes randomly
the source of variation is variation is random (mutations), but the current environmental conditions limit evolutionary change to only those variations
inheritable variations that improve a populations reproductive fitness
natural selection restricts which genes are passed on to the next generation
natural selection involves organisms trying to adapt
Lamarcke’s evolutionary view, which was rejected because traits are not passed to the next generation through acquired characteristics
natural selection gives organisms what they need
if a population has genetic variation that allows some individuals to survive a stress better than others (ex. reproductive fitness), then these individuals will leave more offspring in the next generation
if there is no genetic variation, no evolution will occur
evolution is just a theory
true, because a theory is an explanation of some aspect of the natural world that is well substantiated by multiple lines of independent evidence
central premise of the evolutionary theory:
life has existed for billions of years
life changes over time
life has changed with descent through modification by natural selection
Lamarcke’s Evolutionary View
inheritance of acquired characteristics
idea that one individuals acquired traits can be passed to the next generation
rejected because traits passed to next generation through genes, not acquired characteristics
use and disuse
individual body parts that are frequently used become stronger and more developed, body parts not used deteriorate over time
rejected because of functionality and time scale
functionality: lamarck’s theory implies every change in use leads to a corresponding change in structure’s development
time scale: lamark’s implies rapid adaption based on immediate circumstances
with true evolution, mutations/variations will accumulate over generations and evolution preserves traits that no longer provide any functional advantage, but genes still exist (vestigal structures)
ex. blind mexican tetra: eyes initially develop but muations cause then to become nonfunctional remnants because they live completely devoid of natural light
22.1: Historical Roots that Led to Darwin’s Proposal
Georges Cuvier (1769-1832)
french scientist
noticed that the older the stratum, the more dissimilar its fossils were to the current life-forms
observed that some new species appeared while others disappeared
inferred that extinctions must have been a common occurrence, but opposed the idea of evolution
James Huton (1726-1797)
scottish geologist
proposed that earth’s geologic fetures could be explained by gradual mechanisms, such as valleys being formed by rivers
idea that change happens over a large amount of time
Charles Lyell (1797-1875)
leading geologist of darwin’s time
incorporated hutton’s thinking ito his proposal that geological processes are operating today at the same rate
Jean-Baptiste de Lamarck (1744-1829)
french biologist
introduced the idea that species change, evolutionary change explains patterns in fossils
Thomas Malthus (1766-1834)
every species has the potential for unlimited growth but that doesn’t happen because of environmental constraints
Versalius (1514-1564)
trust your own observations
Charles Darwin developed a scientific explanation for the diversity of life, detailed in his book The Origin of Species.
Darwin's ideas marked the beginning of the era of evolutionary biology.
Darwin's revolutionary ideas were influenced by the work of others and his travels.
Key influences on Darwin's ideas include:
1795: Hutton's principle of gradualism.
1798: Malthus's Essay on the Principle of Population.
1809: Lamarck's hypothesis of evolution.
1812: Cuvier's studies of vertebrate fossils.
1830: Lyell's Principles of Geology.
1831-1836: Darwin's voyage on the HMS Beagle.
1844: Darwin writes his essay on descent with modification.
1858: Wallace sends Darwin his hypothesis of natural selection.
1859: Publication of On the Origin of Species.
The orchid mantis is part of the Mantodea group, which includes 2300 species in 430 genera, all sharing features like three pairs of legs, triangular heads with bulging eyes, and flexible necks.
These shared features illustrate the unity of life, indicating that all organisms share certain characteristics.
Despite their unity, species also exhibit diversity, differing in size, shape, and color.
The orchid mantis and its relatives highlight three key observations about life:
Organisms are well-suited (adapted) for life in their environments.
There are many shared characteristics (unity) of life.
There is a rich diversity of life.
Darwin aimed to explain these observations, leading to the conclusion that life evolves over time.
Evolution is defined as descent with modification, where species accumulate differences from their ancestors as they adapt to different environments over time.
Evolution can also be defined as a change in the genetic composition of a population from generation to generation.
Scala Naturae and Classification of Species
Aristotle's Influence: Aristotle viewed species as fixed and unchanging, arranging life forms on a scale of increasing complexity called the scala naturae.
Old Testament Consistency: Aristotle's ideas aligned with the Old Testament, which held that species were individually designed by God and perfect.
Linnaeus' Contribution: Carolus Linnaeus developed the binomial nomenclature system for naming species, which is still in use today.
Nested Classification: Linnaeus introduced a nested classification system, grouping similar species into broader categories (genus, family, etc.).
Evolutionary Relationships: Unlike Linnaeus, Darwin argued that classification should be based on evolutionary relationships.
Modern Approaches: Modern scientists use molecular approaches to classify species based on evolutionary relationships rather than just visual similarities.
Ideas About Change over Time
Fossils and Sedimentary Rocks: Fossils, the remains or traces of past organisms, are often found in sedimentary rocks formed from sediment settling in aquatic environments. These rocks form layers called strata, with each stratum representing a different time period.
Formation of Strata: New sediment layers cover older ones, compressing them into strata. Erosion can later expose deeper, older strata.
Georges Cuvier's Contributions: Cuvier, a French scientist, noted that older strata contained fossils increasingly dissimilar to current life forms. He inferred that extinctions were common and attributed the boundaries between strata to catastrophic events, followed by repopulation from other areas.
James Hutton's Theory: Hutton proposed that Earth's geologic features could be explained by gradual mechanisms, such as valleys formed by rivers.
Charles Lyell's Influence: Lyell expanded on Hutton's ideas, suggesting that the same geologic processes observed today have been operating at the same rate throughout Earth's history. This concept influenced Darwin's thinking about the age of Earth and the processes of biological change.
Darwin's Reasoning: Darwin agreed with the idea of slow, continuous geological processes, leading him to conclude that Earth must be much older than previously thought. He extended this reasoning to biological evolution, suggesting that slow and subtle processes could lead to significant biological changes over time.
Lamarck’s Hypothesis of Evolution
Jean-Baptiste de Lamarck was a French biologist who proposed a mechanism for how life changes over time.
Lamarck's hypothesis, published in 1809, suggested that evolutionary change explains patterns in fossils and the match of organisms to their environments.
He proposed two main principles:
Use and disuse: Parts of the body that are used extensively become larger and stronger, while those that are not used deteriorate (e.g., a giraffe stretching its neck to reach high leaves).
Inheritance of acquired characteristics: Organisms could pass modifications acquired during their lifetime to their offspring.
Lamarck believed that evolution occurs because organisms have an innate drive to become more complex.
Although Darwin rejected the idea of an innate drive for complexity, he also considered the inheritance of acquired characteristics as a source of variation.
Modern genetics refutes Lamarck's mechanism, showing that traits acquired during an individual's life are not inherited.
Despite being vilified in his time, Lamarck recognized that the match of organisms to their environments can be explained by gradual evolutionary change and proposed a testable explanation for this process.
22.2: Descent with Modification by Natural Selection
Charles Darwin (1809-1882)
notived that individuals vary within populations and we have been practicing artifical selection for 1000s of years
descent: share traits with common ancestor
modification: accumulation of differences
natural selection: mechanism by which change occurs
species change over time, new species arise from common ancestors
as species diverge, they retain some ancestral traits but modify them to suit new environmental functions
in a limiting situation (ex. habitat, environment), individuals with better suited traits to that habitate are more likely to leave more offspring than other individuals
if these better suited traits are hereditary, it is more likely that these traits will become more dominant in subsequent generations, which leads to evolution by natural selection
over the course of enormous amounts of time, the earth/environment is continuously changing
what was better suited at one time may no longer be suitable later, species either adapt via natural selection or go extinct
if species adaptation leads to reproductive isolation, new species arise
ex. giraffes
a long time ago, population of short neck giraffes with some slightly longer and some slightly shorter
environmental stress, contstrainsm and behaviour: slightly longer necked giraffes reproduce more to the next generation
over many generations, the average giraffe length gets longer
22.3: Lines of Evidence
direct observations
ex. invasive species
when a species is introduced to a new environment, it often undergoes rapid evolutionary changes to adapt to the new conditions
soapberry bugs feed on the seeds of balloon vine plants
when introduced to new areas, adapted by evolving shorter beaks to feed more efficiently on the seeds
change was observed over a relatively short period of time and demonstrates natural selection
illustrates darwin’s idea of descent with modification, where species evolve over time due to environmental pressures
ex. drug resistance bacteria
staphylococcus aureus as an eample of rapid evolution through natural selection
methicillin resistant strains of the bacteria emerged shortly after methicillin was introduced ni 1959
methicillin deactivates a protein important for bacterial cell wall synthesis
some bacteria could synthesize their cell walls using a different protein unaffected by methicillin, which allowed them to survive and reproduce
these resistant strains became more common over time
MRSA strains can exchange genes which increases genetic diversity and leads to multidrug resistance
pesticide resistance - OFFICE HOURS
early 1900s, citrus growers were significantly compromised by scale insects
1st generation: used lead, arsenic, and mercury to destroy
early 1900s was 97% effective, onlly 3% effective by 1930
2nd generation: used organochlorines
1938: identified DDT, which does not break down and impacts all insects
in 1946: 1 kilogram or pesticide used for 60 000 bushels of corn, in 1971: 64 kilograms needed for the same amount
resistance increased, leading to secondary outbreals and resurgence
3rd generation: species selective compounds introduced
pyrethroids
insect growth regulators
neonicotinoids
4th generation: biological and biochemical
GMOS, biotechnology
issues with GMOS and biotechnology limit full capacity
RNA interference
homology and vestigial structures
homologous structures = anatomical features in different species that share a common ancestry, even if they serve different functions
ex. vertebrate embryos echibit homologous structures
develop into gills in fish and parts of the ear and throat in mammals
ex. pelvic bones in humans and snakes
different functions, but tha same structures
illustrate how diverse species evolved from common ancesors through descent with modification
vestigial structures = remnants of features that were functional in ancestors but have lost their original purpose
ex. leg remnants in snakes, eye remnants in blind cave fish
indicate a shared ancestry among species, supporting the idea that species have evolved over time from common ancestors
fossil record
provides a chronological account of life on earth
fossils reveal the sequence in which different species appeared and evolved
record demonstrates that many past organisms were unlike those living today and many species that were once common are now extinct
transitional species
ex. aetiocetus (25 MA) as a transitional species
pakicetus (50 MA), described as early ancestor to modern whales
nostrils move from terrestrial —> marine (front to back), should expect a species with nostrils in the middle
biogeography
distribution of species and ecosystems in geographic space and through geological time
concept of continental drift
250 million years ago, all landmasses joined in a supercontinent called pangea
as pangea broke apart, species were isolated on different continents, leading to divergent evolutionary paths
geographic isolation and subsequent evolution can be observed in the fossil record
ex. evolutionary history of horses shows that they orginated in north america, because north and south america werre not connected at that time the oldest horse fossils
helps us understnad how species have evolved in response to their environments and geographic constraints