The Challenges of Making a Living

Learning Objectives1. Review the levels of organization in living things, the importance of homeostasis, &

how this stable internal environment (within the “zone of tolerance”) is maintained.2. Differentiate between short-term and long-term adaptations. Explain the genetic

component of homeostatic mechanisms as well as long-term adaptations to the environment.

3. Describe the similarities and differences among behavioral, cellular, and genetic adaptations, including examples of each.

4. Describe the potential mechanisms of genetic adaptation, and explain how these genes & the natural environment interact.

5. Explain Charles Darwin’s 4 postulates regarding the origin of species, in the context of his observations about populations.

6. Describe several examples that provide additional evidence that populations evolve, potentially producing new species, by the process of natural selection. How are the results of natural selection different from the other processes of evolution?

7. Compare and contrast the evolutionary processes known as genetic drift and gene flow.

8. Compare and contrast stabilizing selection, directional selection, and disruptive selection.

Structural Organization• Most plants and animals have

cells, tissues, organs, and organ systems

• A plant or animal body becomes structurally organized during growth and development– Growth: cells increase in number,

size, volume– Development: specialized tissues,

organs, and organ systems form• Animals have “control centers” to

regulate body function in the short-term, whereas plants have decentralized control over function

What are some of the challenges associated with large body size?

If all somatic cells in an organism have the same genetic information, how can cells specialize into tissues & organs?

p. 404

Homeostasis = the maintenance of a dynamic equilibrium

• Plant and animal cells must be bathed in a relatively stable fluid that delivers nutrients and carries away metabolic wastes in order to stay alive

– Why might an organism’s internal environment change?

– Why is a stable internal environment important to an organism’s survival? Describe an example.

p. 7p. 405

Maintaining HomeostasisWhat are the common challenges?

• O2 & CO2 gas exchange

• water-solute balance• signaling molecules to

guide events on the cellular level

• live within specific habitats, and respond to environmental threats

• Behavioral adaptations– e.g. thermoregulation

• Cellular adaptations– e.g. aclimatization– intercellular communication

• Genetic adaptations– new allele combinations– mutations

Describe an example of a mechanism to adapt to short term changes in the environment. Is your example a behavioral or cellular adaptation? Where does it occur, and how long does it last?

Describe the scope of a genetic adaptation in terms of the number of individuals affected, and the time period over which it occurs.

p. 406

Internal ConditionHighLow

Optimum range

homeostasis

Stress Stress

IntoleranceIntolerance

High

# in

divi

dual

s

Stable operating conditions in the internal environment (in the blood and tissue fluid) is maintained by the coordinated activities of cells, tissues, organs, and organ systems

Zone of Tolerance

Behavioral Adaptations

Cellular Adaptations

Genetic Adaptations

– Crossing Over– Independent assortment– Fertilization– New alleles (gene mutations)

How do genetically derived adaptive traits within a population come about?

Describe how a genome might be changed by these 4 mechanisms.

How might the gene pool be altered when these sources of variation arise?

Gene Pool

http://www.brooklyn.cuny.edu/bc/ahp/LAD/C21/C21_GenePool.html

What is a gene pool?

What is the relationship between a gene pool and a popluation?

What might cause changes in the gene pool?

Is this evolution?

p. 246

Gene Mutation

• Change in the structure of DNA in gametes.

p. 248

Amino acid redundancy allows for fewer mutations

Figure similar to one on p. 198

• Rare!– 1 gamete in 100,000-

1,000,000

• Neutral (why?)• Deleterious

– Changes the shape of a protein

– Stops synthesis of a protein too early

• Advantageous

Gene Mutation

What will likely happen to deleterious mutations in a population?

p. 248

Charles Darwin’s radical idea (…or was it?)

• Meticulous observation• Considered numerous

possible relationships, especially b/w animals and their environment

• 2 main points:– Species evolved from

ancestral species– Natural selection was

the mechanism for this evolutionary change

What is a species?

p. 242

On the Origin of Species• Descent with modification

(aka evolution) is the explanation for life’s unity and diversity– all organisms are related

via a common ancestor– adaptations developed as

descendents from a common ancestor moved into new habitats (or the habitat changed)

Darwin’s metaphor for the history of life was a branching tree.

Observation 1

• Species have a great potential for reproduction

• Populations would increase exponentially if all individuals survived and reproduced

p. 243

Observation 2

• Populations tend to remain stable over time, except for mild seasonal fluctuations and occasional severe fluctuations

Moose population on island in Lake Superior

p. 243

Observation 3• Natural resources are limited, i.e. there is a

struggle for existence

p. 243

Observation 4• No two individuals are exactly

the same; rather, every population displays enormous variability.

p. 243

Observation 5

• Much of this variation is heritable

• However, Darwin did not know the mechanism of inheritance

p. 243

Darwin’s 4 postulates

1. Individuals within species are variable.

2. Some of these variations are passed onto offspring.

3. In every generation, more offspring are produced than can survive.

4. Survival and reproduction are not random. The individuals that survive and go on to

reproduce, are the ones with the most favorable variations.

p. 243

Other Evidence for Evolution

• Organisms are adapted to their environments

• Camouflage is an example of evolutionary adaptation

A floral mantid (insect pollinator)

Other evidence

• Examples of “natural” selection over short periods of time

Evolution of resistance to insecticides in insect populations

Is it fair to describe this as natural selection?

How is this similar to antibiotic resistance among pathogenic bacteria?

Other evidence• Selective breeding & artificial selection

Vegetables developed by humans from wild mustard plant through selective breeding

Other evidence• Homologous structures

Forearm bones in mammals

Other evidence

• Molecular “record” – molecular homologies

Ribosomal structure (large subunit of bacterial ribosome)

Other evidence• Fossil record

Fossil Trilobites

Elephant evolution based on fossils

Alterations to the Gene Pool: Gene flow

• As individuals or gametes flow between populations, they become more similar. The reverse is also true.

p. 255

Alterations to the Gene Pool: Genetic Drift

• With low population size, alleles (i.e. traits) can disappear

How might this happen?

Has evolution occurred?

Is the population more fit?

p. 254

Alterations to the Gene Pool: Directional Selection

Deaths due to pesticides decreased over time.

What determines which alleles are selected?

p. 249

Alterations to the Gene Pool: Stabilizing Selection

Previously, those babies that were too small did not survive and those that were too big had complications.

Does this imply that birth weight is an inherited trait?

p. 250

Alterations to the Gene Pool: Disruptive Selection

Large billed individuals crack hard seeds.

Small billed individuals crack soft seeds.

Intermediate forms do not crack either seeds well.

p. 251