Evolution

Scientists

Carolus Linnaeus 

• First to group similar organisms and assign them Latin names

• Developed 2 word name - genus species

• Also known as binomial nomenclature

Charles Lyell

• Proposed theory of uniformitarianism

• Geological processes at uniform rates building and wearing down Earth’s crust

• One of the first to propose that the Earth was millions of years old instead of a few thousand   

• Published Principles of Geology just before the Beagle (Darwin’s boat) set sail

• Principles of Geology explained geological processes that shaped the Earth

• Darwin read Principles of Geology and it helped Darwin understand sea shells in the Andes mountains at 12,000+ feet above sea level

Jean-Baptiste Lamarck

• 1809

• One of first scientists to understand that change occurs over time

• Stated that changes are adaptations to environment acquired in an organism’s lifetime

• Proposed these changes were passed to offspring

• His idea was called Law of Use and Disuse - if a body part were used, it got stronger and if body part was not used, it deteriorated

• Use and Disuse- organisms could change the size or shape of organs by using them or not using them

• Was incorrect, you must adapt to survive

Thomas Malthus

• 1798

• Economist

• Observed babies being born faster than people were dying

• Population size is limited by resources such as food supply

• Multhus reasoned that if the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone

• He realized that death rate will increase to balance population size and food supply

• Darwin realized that Malthus’ principles were visible in nature 

• It was found that plants and animals produce far more offspring than can be supported

• Most offspring die; otherwise the Earth would be overpopulated

Darwin’s Big Idea

Details

• More offspring are produced than can survive to reproduce because there is competition for limited resources, or a struggle for existence

• Individuals exhibit variation in their traits and some of these differences can be passed on to their offspring

Conclusion

• Organisms with the best traits for their environment produce more offspring over time, causing those traits to appear with greater frequency in the population

• He called this “Unequal Reproductive Success” 

• He argued that all species are descended, with modifications, from a common ancestor

• Through descent with modifications, all organisms - living and extinct - are linked on a single tree of life

Evidence of Evolution

Analogous vs. Homologous Structures

Homologous

• Similar structure, different functions

• Related structures that are inherited from a common ancestor

• Structures have different mature forms but develop from the same embryonic tissue

• Ex. provides evidence that all four-limbed animals with backbones descended, with modification, from a common ancestor

• Traits were inherited from a common ancestor, but evolved to serve a new purpose

• Structures may differ in form or function; however they developed similar patterns

Analogous

• Different structure, similar function

• Two organisms that live in the same type of environment may benefit from being able to perform similar functions but that does not mean they have a recent common ancestor

• If they look different on the inside organisms do not have a common ancestor

• If they look similar on the outside the outside looks similar because they have the same function

Vestigial Structures

• Structures or organs that can still be found in/on an organism that are no longer functional 

• Ex. appendix in humans, pelvic bone on whales, legs on snakes

• Structures are what is left of a specific structure in a common ancestor

Biogeography

• The geographic locations where its fossils are or will be found

• Ex. Today the lungfish neoceratodus fosteri is found only in northeast Australia. Its ancestors lived during the time of Pangea; therefore, these fossils are found on all continents except Antarctica.

• Ex. biogeography of whale fossils matches the pattern predicted by evolution

• All early species of whales that lived in rivers and lakes, but did not swim in the ocean, are found near India and Pakistan. 

• All fully aquatic protocetids are geographically much more widespread because they were good swimmers. 

• Continental islands have many examples of adaptive radiation from a single mainland ancestor

• Ex. Galapagos finches

• Ex. lemurs on Madagascar

Molecular Evidence

• DNA Sequence Similarity: the measure of how closely related two DNA molecules are to each other

• All living organisms on Earth use DNA as their hereditary of genetic material

• All living organisms on Earth use the same genetic code to build proteins

• The universality of the genetic code is one of the strongest pieces of evidence that all living things evolved from a common ancestor

• Similarity between DNA sequences of genes and amino acid sequences of proteins points to common ancestry among species

Fossil Records

• Enables biologists to reconstruct the history of life on Earth

• Provides some of the strongest evidence that species have evolved over time

• Transitional Fossils: evidence of species with some similarities to the ancestral group (land-living mammals) and some similarities to the descendant species (whales)

• The ages of fossils correspond to their depth or distances from the surface of Earth (older fossils are found deeper, in older rock layers)

Comparative Embryology

• Embryonic Development: how an organism develops from a zygote into its full form at birth

• Similarities in different organisms show that characteristics arose through evolutionary modifications of traits from common ancestors

• Ex. gill slits and tails during development of humans

• Complex structures in descendant species are generally elaborations of structures that existed in their common ancestor. 

• Ex. the embryos of dolphins from weeks 4-9 of development show the formation, and then subsequent loss, of the hind limb buds

Questions

1. What does common ancestry mean? Common ancestry is two or more species that have evolved from a common ancestor.

2. Be able to make inferences about the relationship evolution and selection:

1. What is natural selection? A process where organisms with traits better suited to their environment are more likely to survive and reproduce, leading to gradual change in a certain population over time.

2. What do transitional fossils tell us about organisms? They provide evidence of how organisms evolved over time by showing characteristics of an ancestral species and descendant species. Transitional bridge the gap between different evolutionary stages.

3. What do rock layers, fossils found in differentiating layers of rock, indicate about their age and what can they tell us about how the organism evolved? Deeper and older rock layers represent older organisms and shallower layers represent younger, or more recent organisms.

4. What is actually happening during natural selection? What is actually happening during natural selection is you are adapting or dying. If you adapt you give your adapted trait to your offspring. The fittest, or best adapting to their environment, is the organism that will survive long enough to reproduce.

5. Why do we say populations evolve, not individuals? Evolution refers to changes in the genetic makeup for a group of organisms over generations, and since an individual organism cannot change its genes significantly during its life. Only a population can prove that the change was successful because one organism is a random mutation. Only a whole population adapting can pass these traits to a new generation. 

6. Why are mutations key in the evolution of any organisms? Mutation is the only way to introduce new alleles. Mutation introduces genetic variation within a population, which leads to new traits. If there were no mutations evolution would not occur because organisms would not be able to adapt to changing environments.

7. If natural selection does not mean survival of the fittest…what does it mean? Fittest does not mean best. Natural selection is how you adapt to the environment so you can live long enough to reproduce. 

8. What is artificial selection? Who determines the traits are desirable? Artificial selection is humans choosing which organisms mate with other organisms? Humans determine which traits are desirables and mate organisms that have those traits.

9. Differentiate between punctuated equilibrium and gradualism. Punctuated equilibrium is a theory that suggests that evolution occurs in big changes really quickly in rapid periods of change. A graph displaying puncuated equilibrum shows many corners and straight lines. Gradualism is a theory that suggests evolution occurs gradually over time. Evolution occurs at a slow and steady pace and there are small changes that occur over a long period of time. A graph displaying gradualism has many curved corners and lines.

Extra Vocab

• Evolution: a change in the overall inherited characteristics of a group of organisms (populations) over multiple generations

• Population: a group of individuals of the same species living in a defined area

• Artificial Selection: biological evolution for desired traits caused by human performing selective breeding

• Selective Breeding: process by which humans determine which individuals with desired characteristics will mate  

• Natural Selection: process by which individuals with advantageous inherited characteristics for a particular environment survive and reproduce at a higher rate than do individuals with other, less useful characteristics

• Adaptive Trait: a feature that gives an individual improved function in a competitive environment 

• Common Ancestor: an organisms from which many species have evolved

• Common Descent: the sharing of a common ancestor by two or more different species

• Gene Flow: the genetic additions or subtractions from a population resulting from the movement of fertile individuals or gametes

• Fitness: an organism ability to adapt and survive

• Adaptations: inherited traits that increase an organism's fitness

• Genetic Drift: the change in allele frequencies

Example Questions

Multiple Choice/True and False

• Which animal is a product of artificial selection?

• Pick out statements about evolution that are not true. 

• Does evolution explain the diversification of organisms? Yes 

• While mutations are random the process of natural selection is not. True

• What was your favorite activity while learning about evolution?

• Why is immigration a way to change allele frequency? Migration introduces alleles to new areas, which is gene flow. 

• What are the structures of a body that serve no purpose? Vestigial structures

• Evolution would not occur if variation did not exist within a population?

• Are all variations the result of mutations? No

• Are variations observable? Yes

• Do you get variation from your parents? Yes 

• Where do humans get genetic variation? Recombination in meiosis is one of the ways humans get genetic variation.

• Are fossils of different ages going to be in the same layer of rock? No, the oldest will be on the bottom, and the youngest are on top.

• A whale flipper and a bat wing, what are they examples of? Homologous structures (same structure, different function)

• Darwin was a naturalist who collected many organisms during his travels. What did Darwin use to prove natural selection? Darwin used fossils, geology, and studying different populations of organisms. 

• Did Darwin understand artificial selection? Yes

• Did Darwin study populations? Yes 

• Did Darwin understand geology’s connection to evolution? Yes

Short Answer

• Why do we say populations adapt and not individuals?

• Give me four categories of evidence of evolution and examples of each.