Chapter 22: Descent with Modifications ( A Darwinian View Of Life)

What causes the similarities and differences among earths many different species?

-Ancient common ancestors → species accumulate differences from their ancestors as they adapt to different environments over many generations.→ Descent with modifcation 

In descent with modification what does “descent” mean 

shared ancestry, resulting in shared characteristics 

In descent with modification what does “modification” mean

accumulation of differences that arise as species adapt to their environments over time.

What did the Darwinian revolution challenge 

challenged traditional views of a young Earth inhibited by unchanging species 

What book publication started a scientific revolution (the era of evolutionary biology)

Publication of The Origin of Species by Charles Darwin in 1859

How did Darwin’s ideas develop gradually

through the influence of other’s works and his own travels 

Timeline starts 1790 in 1795

Hutton proposes his principle of gradualism 

Timeline 1798

Malthus publishes “Essay on the Principle of Population”

Timeline 1809

Charles Darwin is born + Lamarck publishes his hypothesis of evolution

Timeline 1812

Cuvier publishes his extensive studies of vertebrate fossils

Timeline 1830

Lyell publishes Principles of Geology

Timeline 1831-1836

Darwin travels around the world on HMS Beagle

Timeline 1844

Darwin writes his essay on descent with modification

Timeline 1858

While studying species in the Malay Archipelago, Wallace sends Darwin his hypothesis of natural selection 

Timeline 1859 (-timeline ends in 1870)

The Origin of Species is published

What does Evolution refer to?

Evolution refers to the process by which species accumulate differences from their ancestors as they adapt to different environments over time. → this definition is summarized by Darwin’s phrase “descent with modification” 

Evolution can be viewed as both a pattern and a process therefore define both

-pattern: revealed by scientific data showing that life has evolved over time

-process: consists of the mechanisms that cause the pattern of change 

What did Greek Philosopher Aristotle (384-322 BCE) believe?

He believed that species were fixed (unchanging) 

What else did greek philisopher Aristotle do?

He arranged species on a scale of increasing complexity called the scala naturae

In the 1700s, what did scientists interpret adaptations as 

scientists interpreted adaptations as evidence of design by a Creator

What did Carolus Linnaeus develop form 1707-1778

-He developed a nested classification system grouping similar species into increasingly inclusive categories.

 -also developed binomial format for naming species ex: humans = Homo sapiens

**both of these systems are still in use today

Who drew from the study of fossils

Darwin drew from the study of fossils, remains or traces of organisms from the past 

Where are many fossils found?

Found in sedimentary rock, which appears in layers called strata

Where are younger stratum with more recent fossils located

on the top layer of sedimentary rock

Where are older stratum with older fossils

more towards the bottom/older layers of the sedimentary rock

Who developed the study of fossils, Paleontology

Paleontology, the study of fossils was developed in large part by Georges Cuvier (1769-1832)

What did Cuvier observe? (in Paleontology) 

Cuvier observed that older strata contains fossils less similar to current organisms than more recent strata

and observed that from layer to layer, new species appear while others disappear

What did Cuvier speculate

Curvier speculated that boundaries between strata represents sudden catastrophic events

What was Darwin also influenced by?

Darwin was also influenced by scientists proposing that slow, continuous processes caused change on Earth.

What did James Hutton propose ( 1726-1797)

He proposed that Earth’s geologic features were formed gradually

example: valleys being formed by rivers 

What did Charles Lyell (1797-1875) propose?

He proposed that the same geologic processes operate today as in the past, at the same rate

What did Darwin reason?

Darwin reasoned that the Earth must be older than the widely accepted age of a few thousand years

(if true, gradual processes could also account for substantial biological change)

Lamarck’s hypothesis of evolution

Jean-Baptiste de Lamarck (1744-1829) proposed two principles to explain evolutionary change

(use and disuse + inheritance of acquired characteristics) 

What was Lamarck’s use and disuses principles :

Use and Disuse: body parts used extensively become larger and stronger, unused parts deteriorate 

What was Lamarck’s Inheritance of acquired characteristics:

Modifications acquired in one’s lifetime can be passed to offspring

(this mechanism is not supported by experimental evidence)

What was going on by the early 19th century in term of descent with modifications

By the early 19th century, it was still generally thought that species were created and remained unchanged however doubts were beginning to gather.

Through Darwin’s research what was he doing/studying (1809-1882)

-had a consuming interest in nature throughout his life

-he studied medicine (UNSUCCESSFULLY) and then switched to theology at Cambridge University 

-After graduation, he took a position as naturalist on a five year, worldwide voyage on the HMS Beagle

The Voyage of the Beagle - what did darwin collect during his travels

During his travels on the Beagle, Darwin collected specimens of South American plants and animals 

What did Darwin note regrading fossils during his voyage of the beagle

He noted that fossils resembled living species from the area in which they are found, and living species resembled other species from areas nearby   

What did Darwin notice during an Earthquake in Chile -the voyage of the beagle

He observed the uplift of rocks by several meters

-he inferred that rocks containing fossils of ocean organisms in the Andean Mountains must have been raised there by many similar earthquakes

During the Voyage of the Beagle- What did Darwin do on the Galapagos Island

Darwin collected many similar, but different species of birds, some unique to individual islands and others found on multiple islands 

When Darwin realized animals unique to the islands resembled species on the nearby mainland of South America what did he hypothesize

Darwin hypothesized that species from the mainland colonized and then diversified on the islands 

Darwin’s focus on adaptations - what are adaptations

Adaptations are inherited characteristics that enhance an organism’s survival and reproduction in specific environments.

When Darwin was focused on adaptations what did he perceive regarding new species

Darwin perceived that new species could arise from ancestral forms through gradual accumulation of adaptations

-this process formed the diverse group of Galapagos finches

What did Darwin propose as an explanation for adaptation

Darwin proposed natural selection as an explanation for adaptation

What is Natural Selection a process for

Natural Selection is a process in which individuals with certain inherited traits tend to survive and reproduce at higher rates because of those traits 

Although Darwin wrote down his ideas in 1844, why did he not publish 

He did not publish out of concern they would cause an uproar however he continued to compile supporting evidence 

What did Alfred Russel Wallace (1823-1913) send to Darwin in June 1858

He sent Darwin a manuscript describing a nearly identical hypothesis of natural selection. 

When were papers by both Wallace and Darwin presented and to who?

Papers by both Wallace and Darwin were presented to the Linnean Society of London on July 1, 1858 

Most scientists were convinced of what - within a decade

Most scientists were convinced that life’s diversity is the product of evolution

What were the three broad observations that descent with modifications by natural selection explains

1) The unity of life

2) The diversity of Life

3) The ways organisms are suited to life in their environments 

What did Darwin use to describe his view of life

Descent with Modification

Explain Darwin’s view of life regarding descent with modification 

by this view, all organisms are related by descent from a common ancestor that lived in the past 

Ideas from the Origin of Species 

Related organisms living in different habitats gradually accumulated diverse modifications to fit them to specific ways of life 

How did Darwin view history of life as a tree?

He viewed the history of life as a tree with multiple branching from a common trunk

History of life as a tree - what did the branches represent

groups of organisms living in the present day

History of life as a tree - what did the unlabeled branches represent

extinct groups

History of life as a tree - what does the fork represent

the most recent common ancestor of all lines of evolution branching from that point

What did branching and extinction events explain

Large morphological gaps btwn related groups are explained by branching and extinction events 

examples of morphological gapes btwn related groups - by branching & extinction events

-living elephant species are similar bc they are split from a recent common ancestor 

-extinction of seven older species helps explain the dissimilarity btwn elephants and their nearest living relatives, hyraxes and manatees. 

Artificial Selection?

Humans modify species through artificial selection, breeding only individuals with desired traits 

(crops, livestock animals, and pets often bear little resemblance to their wild ancestors)  

Darwin drew 2 inferences from 2 observations -What were the 2 observations

1) Members of a population often vary in their inherited traits

2) All species can produce more offspring than the environment can support, and many of these offspring fail to survive and reproduce

Darwin drew 2 inferences from 2 observations- what were the 2 inferences

1) Individuals with inherited traits that increase survival and reproduction is an environment tend to produce more offspring than other individuals 

2) The unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations. 

What did Thomas Malthus write abt the capacity of human populations

capacity of human populations to increase faster than critical resources

(darwin recognized this capacity in all species) 

What happens to the rest of the offspring is only a fraction completes development & reproduce

the rest are starved, eaten, unmated, diseased, or intolerant of physical conditions

What happens if Advantageous traits increase the number of offspring that survive and reproduce 

then they will appear at a higher frequency in the next generation 

ex: offspring may inherit a trait that helps them escape predators/obtain food 

What can increase the proportion of favorable traits in the population.

Over time, natural selection by predators, lack of food, or adverse conditions can increase the proportion of favorable traits in the population 

slight advantages vs less favorable variations

even slight advantages gradually accumulate in the population, while less favorable variations diminish → in this way organisms become better suited for life in their environment

What is the main idea of natural selection

Individuals with certain heritable traits survive and reproduce more than others

How does natural selection affect traits in a population over time?

It increases the frequency of favorable adaptations suited to the environments

How can changing environments influence natural selection

If the environment changes, natural selection may lead to new adaptations which can eventually result in new species.

Do individuals or populations evolve?

Populations evolve, not individuals

What traits can natural selection act on?

Only heritable, variable traits in a population

Why do favorable traits differ in different places or times?

Because the environment varies, so what is favorable also changes with the environment

What is evolution supported by

an overwhelming amount of scientific evidence

How are gaps identified by Darwin in the Origin of Species

New discoveries continue to fill gaps 

What are the four types of data that document the pattern of evolution

-Direct observations 

-Homology 

-The fossil record

-Biogeography

What are two direct observations that provide evidence for natural selection

Natural selection in response to introduced species and evolution of drug-resistant bacteria

Where is Staphylococcus aureus commonly found?

It is commonly found on people (part of normal human flora)

What is MRSA

a Methicillin- resistant strain of S. Aureus that acts as a dangerous pathogen

Does natural selection create new traits?

No - it does not create new traits, it edits or selects traits already present in the population

When can natural selection cause rapid evolution?

In species with short generation times.

What determines which traits are selected for or against?

The current, local environment

What is homology

Similarity resulting from common ancestry

What are homologous structures?

Anatomical resembles that are variations of a structural theme inherited from a common ancestor. 

What does comparative embryology reveal

It reveals anatomical homologies that are not visible in adult organisms

What features do all vertebrate embryos share?

A post anal tail and pharyngeal arches 

Why is comparative embryology reveal

It reveals anatomical homologies that are not visible in adult organisms

What features do all vertebrate embryos share

a post anal tail and pharyngeal arches

why is comparative embryology useful for studying evolution?

It shows shared developmental features that indicate common ancestry

What are evolutionary trees

Diagrams that reflect hypotheses about the relationships among different groups 

What do homologies form in evolutionary trees

nested patterns

What can evolutionary trees be built from?

Many types of data, including anatomical and DNA sequence data

What is convergent evolution

The evolution of similar (analogous) features in distantly related groups

How do analogous traits arise?

When different groups independently adapt to similar environments in similar ways.

What does convergent evolution tell us about ancestry?

Nothing - it does not provide information about common ancestry.

What evidence does the fossil record provide

Evidence of species extinction, the origin of new groups, and changes wihtin groups over time.

What is biogeography

the scientific study of the geographic distribution of species, provides evidence of evolution

Define Pangaea

Earth’s continents were formerly united in a single large continent (pangaea) but have since separated by continental drift

What allows us to predict when and where different groups evolved

An understanding of continent movement and modern distribution of species allows us to do this