Evolution and Scientists

Unit 2 – Evolution

Steps Leading Up to Charles Darwin’s Theory ü Around the world, there is an enormous diversity of life

Each species has its own set of characteristics
Arctic animals – have characteristics that help them survive in the cold, harsh environment
Desert animals – have characteristics that help them survive in the extreme heat ü Theory is a set of statements that explains a group of facts or phenomena

Tested repeatedly and supported by evidence
Can be used to make predictions about natural phenomena ü In the 19th Century, Charles Darwin developed a theory

Designed to explain:
Diversity of life on earth
How all organisms are related to one another and to the environment in which they live
Sought to explain evolution
It is the idea that all species are descendants of ancient species that were different from modern-day species
Biological history of life on Earth, from the earliest micro-organisms to the diversity of modern-day organisms
Two ideas before Darwin’s time
Species are fixed/permanent – do not change over time
Earth is less than 10 000 years old and also relatively unchanging
Changing Ideas About the Natural World ü James Hutton

Scottish geologist
Proposed that rock formations are being continually formed
Molten material is forced up to Earth’s surface to form rock
Studied the rates of present-day erosion and sedimentation and the thickness of bands of sedimentary rock
Concluded that it must have taken millions of years, not thousands, to form the current landscape
Supported the theory of uniformitarianism
States that Earth was formed by slow-moving processes, such as erosions and sedimentation, and still continues to shape our landscapes ü Charles Lyell

English geologist
Popularized and expended on Hutton’s ideas of uniformitarianism in his book Principles of Geology
Found more evidences to support the idea that rock formations were formed by incredibly slow processes that are still at work today ü Georges Cuvier

French naturalist
Compared the bones of modern-day elephants and fossilized mammoths
Concluded that the mammoth’s skeleton was different enough from an elephants’ that mammoths had to be considered a different species and that the mammoth had become extinct
Another example – T. rex ü Jean-Baptiste Lamarck

French naturalist
Recognized that species are not permanent
Proposed that species evolve, or change, over time
Explained that evolution as a process of adaptation
Adaptation is an inherited characteristic that improves an organism’s ability to survive and reproduce in a particular environment
Also proposed a hypothesis to explain how changes in species happen
Realized that organisms were adapted to their environment
Had 3 ideas:
By using, or not using, certain body parts, an organism develops certain characteristics
Ex) giraffes need to reach vegetation high up in the trees à developed long necks
These enhanced characteristics would be passed onto the offspring
Called this idea “inheritance of acquired characteristics”
All organisms have a “tendency towards perfection”
Organisms continuously change and acquire features in order to be more successful in their environments
ALTHOUGH IT SEEMED LOGICAL AT THE TIME, OUR KNOWLEDGE OF DNA AND ITS ROLE IN THE INHERITANCE OF TRAITS DOES NOT SUPPORT LAMARCK’S HYPOTHESIS
An acquired characteristic would have to somehow change the DNA of particular genes in order to be inherited
Nonetheless, he was important in analyzing the role of the environment and explaining evolution as a process of adaptation to the environment
Darwin’s Observation ü In 1831, the HMs Beagle set sail on a voyage around the world

As a naturalist, Darwin collected many fossil records and samples around the world
His main interest was to study the geology, plants, and animals encountered on the voyage ü Patterns in Diversity

Species Vary Globally
Distantly related species living in similar habitats in different parts of the world looked similar and acted in similar ways
Ex) Rheas (S. America) + Emus (Australia) + Ostrich (S. Africa) are all flightless birds living in grasslands
Some areas had unique organisms not found anywhere else in the world
Ex) Kangaroos and other marsupials are found only in Australia
Species Vary Locally
Related animal species that occupied different habitats within a local environment had different features
Noticed this on his trip to the Galapagos Islands
Ex) tortoises in the Isabela Island had greater rainfall, which allowed them to metabolize on vegetation close to the ground à Espanola Island is hot and dry, tortoises have different adaptations to allow them to reach the high, sparse vegetation
He thought different finch species
Initially, he thought these birds were from different bird families because they looked so different from one another
Further examinations showed that they are from same bird families
They were just differently adapted to fit the need of their particular food sources
Species Vary Over Time
Emerged from his study of the South American fossils he found on his journey
Some were gigantic versions of modern-day animals
Species living in South America today were descended from ancestral species on that continent
Also discovered new species that were extinct millions of years ago ü Darwin develops his theory by reading an essay written by Thomas Malthus

He said much of human suffering was due to the human population’s potential to grow
Human populations grow faster than the resources à runs out and struggles for existence, and something must correct it
So, the human population goes over the carrying capacity, but it does not affect the well-being of the human population for a long time but the nature will most likely correct it by pandemic and etc.
DARWIN REALIZED THAT HE CAN APPLY THIS TO THE MECHANISMS OF EVOLUTIONARY CHANGE
Darwin’s Theory

ü When we look at our anatomy, we resemble other animals

Some have similar functions in common with other species
Ex) cat’s front leg = human arms ü Some features are common with other species but has no function for us

Ex) Goosebumps:
Birds – skins contract to raise hair on skin – keeps them warm
Humans – same process, but no function. IT DOESN’T KEEP UP WARM ü In his book The Origins of Species, he has 2 main points:

All species of organism living on Earth today are descended from ancestral species – species evolve over time
The mechanism that cause species to change over time is natural selection
Descent with Modification ü The descendants of the earliest organisms spread into various habitats over millions of years

They accumulated different modifications/adaptations to diverse ways of life
Called descent with modification
Original name of evolution – Darwin never actually used the term
Proved as an explanation of diversity of life
Hares – spread into different environment, they have benefited by having various adaptations that allowed them to thrive in such conditions
Ex) Jackrabbit benefits from fur that blends well in the desert and ears that help cool its body
Ex2) Snowshoe hare benefits from fur that blends well in the snow
They are all from common hare ancestors
Natural Selection: The Mechanism of Evolution ü Struggle for Existence

All species tend to produce excessive number of offspring
But in nature, resources are limited
# of offspring > resource à leads to struggle of the general population of the species
In most cases, small % of offspring will survive in each generation
Rests are starved, eaten, frozen, diseased, unmated, or unable to reproduce for various reasons… (Yeah… let’s not go into that…L) ü Variation

Refers to differences among members of the same species
Ex) @ the classroom, look how many different hair colors, facial colors, etc among the students
Most of the variation is heritable, meaning it passes from one generation to the next
Ex) siblings are more related to each other and to its parents than to other general public (I’m not related to Adolf Hitler… Am I?)
Sometimes a certain variation was best suited to the local environment, and individuals with this heritable variation were more likely to leave the most offspring ü The Role of the Environment

Like Lamarck, Darwin observed that a key factor in the survival of the organism was how well it was suited to the environment. Lamarck though that the environment makes individual organisms acquire characteristic throughout their lives that help them survive in their environment
Darwin explained that there were variations among the member of species
Environment selected those individuals with variations that were best suited for that environment
Ex) Giraffes – some were born with short necks, some were born with long necks à Long necks survived because the environment favored them à reproduced and passed along the good genes
Genetics supports Darwin’s views, not Lamarck’s idea that giraffes grow longer necks during their lifetimes because they need to, and they passed the characteristic to the next offspring
Synthesis of Observations
Natural selection/Survival of the Fittest – the process by which individuals with inherited characteristics well suited to their environment leave more offspring on average than do individuals with adaptations less suitable to the environment
The individuals that function best in the local environment tend to leave the most offspring
This process causes a population to change over time
An organism’s natural surroundings (its ecological niche) determine whether or not it will survive and reproduce
Darwin’s theory of evolution = natural selection as the mechanism of evolution. The result of natural selection is adaptation.
Evidence for Evolution

Fossil Record ü The younger rock layers are deposited on top of older ones

Positions of fossils in the rock strata can reveal their relative age
Deeper the layer in which the fossil is found, the older the age of the fossil ü The fossil record is this chronological collection of life’s remains in the rock layers, recorded during the passage of time

ü Paleontologists discovered fossils of many ancestral life form that link the past with the present

Supports the hypothesis that whales, which have no hind limbs, evolved from land-dwelling ancestors that had 4 limbs ü Can also provide evidence of the extinction of some species

Shows the sudden disappearance of dinosaurs ü Limits – species that do not possess hard tissues such as bones and shells rarely become fossilized

Geographic Distribution ü Closely related but different

Ex) finches
They were all descendents of a single ancestral species from the South American mainland
Became geographically isolated ü Distantly (Geographical-wise) related but similar

Ex) sometimes similar habitats select for similar adaptations
Beaver, muskrat, capybara, and coypu all live in different habitats, but they are closely related to each other
Comparative Anatomy ü Homologous Structures

Similar structures in species that share a common ancestor
Structures that originally functioned one way in ancestral species become modified as they take on new functions ü Vestigial Structures

Remnants of structures that may have had an important function in an ancestral species but have no clear function in some modern descendants
Ex) appendix – reduced in size due to a change in the human diet à we’re not vegetarian, we’re omnivores
May have been a secondary use in the immune system
It had lost its original function ü Analogous Structures

Distantly related species develop structures that are anatomically different but the structures’ functions are the same
Ex) Butterfly’s wing & Bird’s wing
Comparative Embryonic Development ü Embryo of closely related organisms often have similar stages in development

Vertebrates all have an embryonic stage where pharyngeal pouches appear on the side of their throat,
As development progresses, these vertebrates take on more distinctive features
Fishes – pharyngeal pouches turn into gills
Molecular Biology ü The ordered sequences of the components that make up DNA molecules are passed from parents to offspring

Provide a record of an organism’s ancestry ü Ex) you can compare the number of amino acids that differ from human hemoglobin chain (total length = 146 amino acids)

ü Ex) Cytochrome C is another protein found in all organisms that need oxygen to survive – helps them with cellular respiration. Humans and chimpanzees have identical amino acid sequences and that means they are more likely to be related to each other and diverged from a common ancestor

Evidence for Natural Selection

Artificial Selection ü Selective breeding of domesticated plants and animals to produce offspring with genetic traits that humans value

Ex) when buying a pet or an animal, one might look for growth rate and temperament
Breeders do what the environment does in natural selection
Ex) dogs – humans have been modifying dog for thousands of years
Changes in Beak Shape ü The Grants showed that the beak shape and sizes change as El Nino come and go

ü During the wet years, seeds are soft and on the ground, they don’t need a big beak to eat it – so smaller beak

ü During the dry years, seeds are hard and they need big beak to break open the seed shell – bigger beak

Antibiotic Resistance in Bacteria ü Tuberculosis

The drug Streptomycin was discovered in the 1950s to treat tuberculosis
By the 1970s they are all wiped out
In 2007 the TB went on a rampage
They have many variations, some can be destroyed by antibiotics, and some are more resilient. That means through natural selection and survival of the fittest, they are able to reproduce and their population increases