Chapter 19 - Descent with Modification

What book did Charles Darwin publish and what did it focus on

The Origin of Species (1859)

• focused the great diversity of organisms

Descent with modification

• noted that current species are descendants of ancestral species

• explains the adaptations of organisms and the unity and diversity of life

is evolution a pattern or a process

• evolution is BOTH a pattern and a process

Carolus Linnaeus

• founder of taxonomy

taxonomy

• branch of biology that classifies organisms

what helped lay the groundwork for Darwin’s ideas

the study of fossils

strata

layers of sedimentary rock where fossils can be found

• younger stratum with newer fossils on top

• older stratum with older fossils on bottom

Georges Cuvier

• developed paleontology, the study of fossils

• advocated catastrophism

  • speculated that each area between strata represents a catastrophe

paleontology

study of fossils

james hutton and charles lyell

• perceived that changes in Earth’s surface can result from slow continuous actions still operating today

uniformitarianism

lyell’s principle that states that the mechanisms of change are constant over time

• strongly influenced Darwin’s thinking

Lamarck’s hypothesis of evolution

• species evolve through use and disuse of body parts and the inheritance of acquired characteristics

• this hypothesis lacks evidence

what did Darwin first study

medicine (unsuccessfully) because he didn’t like the sight of blood

• and then theology at cambridge university

what boat did Darwin voyage on and what did he do

• HMS beagle

• darwin collected specimen of south american plants and animals

• observed adaptations of plants and animals that inhabited many diverse environments

what influenced Darwin in his studies

Lyell’s Principles of Geology

• Darwin thought that the earth was more than 6,000 years old

what did Darwin observe after reassessing his trip on the HMS beagle?

• perceived adaptation to the environment and the origin of new species as closely related species

  • based on his findings on finches having various sized/shaped beaks on various islands

Darwin and Wallace

• Darwin wrote an essay on the origin of species and natural selection, but didn’t publish it because he was afraid of getting backlash

• Wallace sent a manuscript to Darwin who had created an identical theory of natural selection as Darwin’s

• Darwin then finished the book and published it the next year

Darwin’s two main ideas in The Origin of Species

1. Descent with modification explains the unity and diversity of life

2. Natural selection is the cause of adaptive evolution

artificial selection (and what Darwin observed)

• humans modifying other species by selecting and breeding individuals with desired traits

  • bred his own pigeons to examine how traits could be altered under strong artificial selection

  • Darwin saw that traits can be altered by selective breeding over many generations

where did Darwin get inspiration for his theory of natural selection

• from his detailed study of artificial selection as practiced by plant and animal breeders

Thomas Malthus

• economist who noted the potential for human population to increase faster than food supplies and other resources

process of adaptation

• heritable traits that are advantageous will accumulate in the population overtime

  • this will increase the frequency of individuals with adaptations

• explains the match between organisms and their environment

summary of natural selection

• individuals with certain heritable characteristics survive and reproduce at a higher rate than others

• natural selection increases the adaptation of organisms to their environment over time

  • as environment changes, natural selection has to catch up

    • may result in adaptation and may give rise to new species

3 conditions for adaptation by natural selection

1. individuals must vary in reproductive success

• some are better at this than others

2. some variation in the trait must be heritable

3. trait must be correlated with reproductive success

can individuals evolve?

no, individuals do not evolve

• populations evolve over time through the accumulation of advantageous traits in individuals

• natural selection can only increase or decrease heritable traits in a population

example of natural selection in birds

• droughts from an el nino year cause smaller seeds to be exposed, which get eaten first by birds

  • this leaves only the bigger seeds left, so then bigger finches with bigger beaks become more advantageous

Was Darwin’s theory of evolution monolithic?

• no it was not a monolithic (singular) theory

• Darwin’s theory of evolution consists of five separate theories

Darwin’s 5 theories of evolution

1. Evolution as such

• organisms change over time

• this is no longer considered theoretical but factual

2. Common descent

• every group of organisms is descended from a common ancestor]

3. multiplication of species

• species multiply by splitting or budding

4. gradualism

• evolutionary changes occur through gradual changes in populations

• sometimes gradual, sometimes not

5. natural selection

• descent with modification

example of evolutionary changes occur through with salmon

• male salmon were advantageous if they were red because females preferred red salmon

  • but if you separate the males and females selectively inside buckets (sexual selection), this advantage is lost

  • and thus the trait is eventually lost

what is a theory in science

a well verified explanation based on a body of facts that have been well tested

what do theories do

• make life easier for scientists

• compress the data of the world for us

• a good theory doesn’t need to have a disconnected series of facts memorized

  • facts should fit a pattern

• ex. the difference between Canadian and American elections

4 lines of evidence for evolution

1. evolution is directly observable

2. homology

3. fossil record

4. biogeography

Trinidadian guppies and how evolution is observable

• brightly coloured males are more attractive to females, but also more vulnerable to predators (pike cichlids)

• guppy populations in pools with fewer pike cichlid predators had more brightly coloured males

antibiotic resistance and how evolution is observable

• most people aren’t affected by the bacterium staphylococcus aureus (found in 1/3 people)

  • but some strains of it are formidable pathogens

• penicillin was a widely used antibiotic that was affective against S. aureus (1943)

  • but within 2 years, 20% of S. aureus were resistant to penicillin

• Methicillin was introduced (1959)

  • within 2 years, resistant strains of S. aureus developed (Methicilin resistant S. Aureus (MRSA))

• Multidrug cocktails were then introduced

  • but still resistant strains emerged

2 key points to evolution of MRSA

1. natural selection just edits among existing variants in a population, it doesn’t create them from scratch

• variants that used a different enzyme to build the bacterial cell wall were initially favoured by selection

2. natural selection depends on time and place

• traits that are advantageous in one population may be disadvantageous elsewhere

why is overuse of antibiotics bad

use antibiotics sparingly and not so much over a short period of time because nonresistant forms of bacterium can surpass resistant forms of bacterium once the antibiotics aren’t present

• since your body is so accustomed to being protected by the effects of the antibiotic, it has lost its ability to protect itself from the original nonresistant form

where are most antibiotics used?

• livestock

Homology

similarity resulting from common ancestry

homologous structures

• anatomical resemblances that represent variations on a structural theme present in a common ancestor

  • ex. common ancestor of all mammals had 4 limbs

examples of homologous structures

• humans, cats, whales, and bats all have similar skeletal structures on their limbs, they just look different due to adaptations to different environments over centuries

• embryos of these animals have similar features as well

  • pharyngeal pouches and post-anal tails in both chick and human embryos

vestigial structures and example

remnants of features that served important functions in the organism’s ancestors

• ex. vestigial hind limbs in boas and pythons

loss of vitamin C and how it relates to vestigial structures

• humans cannot make vitamin C in our bodies, but we have vestigial genes for its synthesis

• rendered non functional by a mutation that disables the terminal step in the metabolic pathway

how many times has the ability to make vitamin C been lost in mammals

3 times

• primates

• guinea pigs

• fruit bats

evolutionary tree

hypotheses about the relationships among different groups

• can be made using different types of data

  • ex. anatomical and DNA sequence data (DNA is the most commonly used in modern day)

convergent evolution

evolution of similar (analagous) features in distantly related groups

• analogous traits arise when groups independetly adapt to similar environments in similar ways

does not provide info about ancestry

the fossil record

• provides evidence of the extinction of species, origin of new groups, and changes within groups over time

the fossil record and evolutionary transitions

• the Darwinian view of life predicts that evolutionary transitions should leave signs in the fossil record

• palaeontologists have discovered fossils of many transitional forms

  • ex. it is not clear where reptiles end and mammals begin

do genes from hind limbs disappear?

no, they don’t disappear, we just turn off the genes for them

Biogeography

the geographic distribution of species

biogeography and continental drift

• earth’s continents used to be united in one large continent called Pangaea but separated due to continental drift

• understanding the movement of the continents and modern distribution of species allows us to predict when and where different groups evolved

what is theoretical about Darwin’s view of life?

• Darwin’s theory of evolution by natural selection combines diverse areas of biological study and sparks many new research questions

• ongoing research adds to our understanding of evolution