Charles Darwin & Natural Selection

How do organisms evolve?

They change over time

What did Darwin notice about fossils?

He noticed that some fossilized organisms no longer exist on the planet and that fossils of organisms do not always resemble their modern-day descendants completely

What are fossils?

Remains or traces of organisms from the past

Where are fossils usually found?

Sedimentary rock

Strata

The layers of sedimentary rock in which fossils are found

What did Jean-Baptiste de Lamarck publish?

Theory of Evolution (1809)

What were Lamark’s main ideas?

Use and Disuse, Inheritance of Acquired Traits, Tendency toward Perfection

Explain Lamark’s Use & Disuse idea

Lamark believed that the more parts of the body were used, the stronger and bigger they would get

Explain Lamark’s Inheritance of Acquired Traits idea

Lamark believed that modifications could be passed on

Explain Lamark’s Tendency toward Perfection idea

Lamark believed that species were made to be perfect and tried to be that way always

Were Lamark’s proposals accurate?

No

What can we learn from Lamark?

We can learn about his realization that species evolved, although his explanation was flawed

How would Lamark vs Darwin describe the evolution of giraffes with shorter necks into those with longer necks as trees grew taller?

**Lamark:** The giraffes had to adapt to reach the trees and get food. The increased use of their necks made it longer, helping them reach the trees.

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**Darwin:** The giraffes with shorter necks died as they could not reach the trees and get necessary food. The longer necked giraffes were able to survive long enough to reproduce, passing their traits onto their offspring, populating the gene pool with the long neck characteristic.

Describe Weissman’s experiment and how it disproves a Lamark theory

Weissman cut the tails off of mice and studied them and their offspring. If Lamark was correct in the assumption that acquired traits were inherited, then the mice wold eventually produce offspring with no tails. This however, did not happen, disproving Lamark’s theory.

Evolution

Change over time in the genetic composition of a population from generation to generation

* Organisms DO NOT choose to evolve; it is not purposeful

What is the Darwinian definition of evolution?

Descent with modification

Descent with Modification

Evolutionary change based on the interactions between populations and their environment with results in adaptations to increase fitness

What are adaptations

An inherited characteristic that gives an organism an advantage

What happens when an individual has certain heritable traits that helps them survive?

They reproduce at a higher rate than other individuals

What does natural selection increase?

The adaptation of organisms to their environment over time

What may happen if an environment changes over time?

Natural selection may result in adaptation to these new conditions and may give rise to new species

What are the 5 major points of evolution by natural selection?

1. Overproduction of offspring
2. Variation exists among offspring
3. Offspring struggle to survive (competition)
4. Survival of the fittest
5. Best adapted reproduce and pass their genes on to their offspring (high fitness)

What does it mean to be ‘fit’?

To be the best adapted

What causes the variation amongst offspring?

**Sexual Reproduction:** Meiosis crossing over, independent assortment, independent fertilization

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**Asexual Reproduction:** Random bases changes in DNA sequences = mutations

Do mutations always pass on?

Nope, only if they’re in sex cells

Why would offspring compete?

Compete to get food, mates, territory, shelter, and to hide from predators

What determines which organisms survive and reproduce?

Nature

Did Darwin know about the causes of offspring variation?

Nope

Who is Charles Darwin and what did he do?

An English naturalist that joined a 5-year research voyage around the world to collect and study nature. He studied plant and animal specimens, bones, and fossils.

In what place did Darwin come up with his most brilliant ideas?

The Galápagos Islands

What was the name of the ship Darwin went on?

The HMS Beagle

Do individuals evolve?

No, populations do. Over time

Can natural selection create new traits?

No, it can only increase or decrease heritable traits that vary in a population, editing or selecting traits that already exist

What determines the traits that are selected for or against in any specific population?

Natural selection and the local environment

What does natural selection favor?

The organisms with traits more fit to survive

True or False: All adaptations are the same

False: They vary with different environments

What did Darwin hypothesize about species in the Galapagos?

He hypothesized that species from South America had colonized the Galápagos and speciated on the islands, occupying new environmental niches

What did Darwin conclude about adaptation?

Environmental adaptation was a closely linked process to the origin of new species

What did Darwin notice about Galapagos finches?

They had beaks that were adapted to eating different food sources on different islands

Did Darwin know about artificial selection?

Yes, he noted that humans have modified other species by selecting and breeding individuals with desired traits

What are examples of artificial selection?

Domesticated animals, agriculture

What is artificial selection also called?

Selective breeding

What are the main pieces of evidence for evolution? Which is the most rock-solid?

Fossils

Homologous Structures

*Similar Biochemistry*: **the most solid** (used to support other evidences)

Similar Embryo Development

Vestigial Structures

Similar Biochemistry

Similar DNA, RNA, and amino acid sequences

* Genes shared among organisms inherited from a common ancestor (molecular level)

Homology

Similarity resulting from common ancestry

Homologous Structures

Anatomical resemblances that represent variations on a structural theme present in a common ancestor (similar anatomy)

What is comparative embryology

The a branch of the study of embryos that reveal anatomical homologies not visible in adult organisms

Vestigial Structures

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

* Whales have leg bones that are vestigial

Why do vaccines have to keep changing for HIV and Covid but not for chicken pox?

HIV and Covid are RNA viruses, which means there is no proofreader when copying genetic material, resulting in many mutations that change the virus properties

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Chicken pox, however, is a DNA virus, which means the proofreader makes sure the DNA copied is the same