All living organisms share five fundamental characteristics: utilizing energy, being cellular, processing information, replicating, and evolving. The cell theory and the theory of evolution by natural selection form the framework of modern biology. A phylogenetic tree graphically represents evolutionary relationships among species based on their genetic similarities and differences.

1. Chapter 1:
Biology and the Tree of
Life

2. All living organisms share five fundamental characteristics
– energy utilization, cellularity, information processing,
replication, and evolution.
Biological science foundation
(1) the cell theory
(2) the theory of evolution by natural selection
A phylogenetic tree is a graphical representation of the
evolutionary relationships among species.
Scientific method hypothesis testing

3. All living organisms share five fundamental
characteristics
– Energy
• All organisms acquire and use energy.
– Cells
• All organisms are made up of membrane-bound cells.
– Information
• All organisms process hereditary information encoded in
genes as well as information from the environment.
– Replication
• All organisms are capable of reproduction.
– Evolution
• Populations of organisms are continually evolving.

4. Theories
• A theory is an explanation for a very general class of
phenomena or observations.
• Theories have two components.
– Pattern
• Something that occurs in the natural world
– Process
• Responsible for creating the pattern
• Two theories form the framework for modern biological
science.
– The cell theory
– The theory of evolution by natural selection

5. The Cell Theory
• Late 1660s, Robert Hooke and Anton van Leeuwenhoek
first to observe cells.
• A cell is a highly organized compartment bounded by a
plasma membrane that contains concentrated chemicals in
an aqueous solution.
• The cell theory states that all organisms are made of cells
and all cells come from preexisting cells.

6. Louis Pasteur’s Experiment
• A hypothesis is a proposed explanation.
• A prediction is something that can be measured and must
be correct if a hypothesis is valid.
• Louis Pasteur proved that cells arise from cells and not by
spontaneous generation.

7. Do Cells Arise Spontaneously?

8. Implications of the Cell Theory
• Because all cells come from preexisting cells, all
individuals in a population of single-celled organisms
are related by common ancestry
• In a multicellular organism, all of the cells present
descend from preexisting cells and are connected by
common ancestry.

9. The Theory of Evolution by Natural Selection
• In 1858, Charles Darwin and Alfred Russel Wallace made
two claims regarding the natural world:
– All species are related by common ancestry (pattern).
– Characteristics of species can be modified from
generation to generation.
• Descent with modification (process)

10. Evolution and Natural Selection
• Evolution is a change in the characteristics of a population
over time. It means that species are related to one another
and can change through time.
• Natural selection explains how evolution occurs.

11. Natural Selection and Populations
• A group of individuals of the same species living in the
same area at the same time constitute a population.
• Two conditions must be met for natural selection to occur
in a population:
1. Individuals in the population vary in characteristics
that are heritable.
2. In a particular environment, certain versions of these
heritable traits help individuals survive better or
reproduce more than do other versions.

12. Evolutionary Change
If certain heritable traits lead to increased success in
producing offspring, these traits become more common in
the population over time. In this way, the population’s
characteristics change as a result of natural selection
acting on individuals.
– Natural selection acts on individuals, but evolutionary
change occurs in populations.

13. Artificial Selection
• In artificial selection, changes in populations occur when
humans select which individuals will produce the most
offspring.
• Repeating this process over generations results in changes
in the characteristics of a domesticated population over
time.

14. Artificial Selection

15. Differential Reproductive Success
• Evolution occurs when heritable variation leads to
differential success in reproduction.
• This can occur via:
– Ar
tifi
cia
l
sel
• Fitness is the ability of an individual to produce offspring.
ect
– Individuals with high fitness produce many surviving io
offspring. n–
hu
• Adaptation is a trait that increases the fitness of an ma
individual in a particular environment.

16. The Tree of Life
• The cell theory and the theory of evolution by natural
selection imply that all species come from preexisting
species and that all species, past and present, trace their
ancestry back to a single common ancestor.
• Speciation is a divergence process in which natural
selection has caused populations of one species to diverge
to form new species.
• The tree of life is a family tree of organisms that describes
the genealogical relationships among species with a single
ancestral species at its base.
• Phylogeny is the actual genealogical relationships among
all organisms.

17. Using Molecules to Understand the Tree of Life
• Carl Woese et al. studied small subunit ribosomal
RNA (rRNA), to understand evolutionary
relationships.
• rRNA is comprised of four chemical units called
ribonucleotides.
– A, U, C, & G
• The sequence of ribonucleotides can change during
evolution.
• Based on the theory of evolution, rRNA sequences
should be very similar in closely related organisms
but less similar in less closely related organisms.

19. The Phylogenic Tree of Life
A phylogenetic tree reflects relationships between
species. Branches that share a recent common ancestor
represent species that are closely related; branches that
don’t share recent common ancestors represent species
that are more distantly related.

21. Changes to the Tree of Life
• The tree of life indicates three major groups of organisms:
– Eukaryotes—Eukarya
– Prokaryotes—Bacteria and Archaea.
• Woese created a new taxonomic level called the domain.
• The location of certain branches on the tree is hotly
debated and the shape of the tree will continue to change
as databases expand.

22. Interpreting the Tree of Life
• The tree of life indicates three major groups of organisms:
the eukaryotes – Eukarya – and two groups of prokaryotes
– Bacteria and Archaea.
• Fungi and animals are more closely related to each other
than either is to plants.
• Traditional classification schemes were often inaccurate.
• The location of certain branches on the tree is hotly
debated and the shape of the tree will continue to change
as databases expand.

23. Taxonomy
• Taxonomy is the effort to name and classify organisms.
– A taxon is a named group.
• To reflect the tree of life, Woese created a new taxonomic
level called the domain, which consists of three taxa:
Bacteria, Archaea, and Eukarya.
• A phylum is a major lineage within a domain.

24. Linnaeus’ Taxonomic System of Classification
• In 1735 Carolus Linnaeus established
the classification system still in use
today.
• Each organism is given a unique two-
part scientific name consisting of the
genus and the species.
– A genus is made up of a closely
related group of species.
– A species is made up of individuals
that regularly breed together or
have characteristics that are
distinct from those of other
species.

25. Rules of Nomenclature
• An organism’s genus and species designation is called its
scientific name or Latin name.
– Scientific names are always italicized.
– Genus names are always capitalized, but species names
are not. (e.g., Homo sapiens or Platanthera integrilabia)

26. Doing Biology: The Nature of Science
• All scientists ask questions that can be answered by
measuring things – by collecting data.
• Science is about formulating hypotheses and finding
evidence that supports or conflicts with those hypotheses.
– For example, using carefully designed experiments,
biologists test ideas about the way the natural world
works by testing the predictions made by alternative
hypotheses.
• On the other hand, religious faith addresses questions that
cannot be answered by data but instead focus on why we
exist and how we should live.

27. Hypothesis Testing
• Hypothesis testing is a two-step process:
1. State the hypothesis as precisely as possible and list
the predictions it makes.
2. Design an observational or experimental study that is
capable of testing those predictions.

28. Why Do Giraffes Have Long Necks?
• The food competition hypothesis argues that long necks
evolved because those with long necks can reach food
unavailable to other mammals.
– Predictions:
• Neck length is variable among giraffes.
• Neck length in giraffes is heritable.
• Giraffes feed high in trees.
• Simmons and Scheepers tested the food competition
hypothesis and found that the third prediction does not
hold true.
– Thus, there may be better alternative hypotheses to
explain neck length in giraffes.

29. http://www.youtube.com/watch?v=C7HCIGFdBt8

30. The Sexual Competition Hypothesis
• An alternative hypothesis is that giraffes evolved long necks
because longer-necked males win more fights than shorter-
necked giraffes, and can then father more offspring.
• Data support this hypothesis.

31. Experimental Design – How Do Ants Navigate?
• Experiments are a powerful scientific tool because they
allow researchers to test the effect of a single, well-defined
factor on a particular phenomenon.
• Wittlinger and colleagues questioned how ants find their
way back to their nest after foraging for food.
– The pedometer hypothesis states that ants always know
how far they are from the nest because they track the
number of steps taken and length of their stride.

32. Experimental Setup
• Wittlinger’s group manipulated the ants into three groups
after walking from the nest to a feeder:
1. Stumps – legs were cut to form shorter-than-normal
legs
2. Normal – individuals were left alone with normal legs
3. Stilts – bristles glued on legs to form longer-than-
normal legs
• Measured the distance the ants traveled back to the nest
via a different route

34. Results and Conclusion
• A null hypothesis specifies what we should observe if the
hypothesis being tested doesn’t hold.
• Results:
– “Stumps” stopped short of the nest.
– “Normal” ants returned to the nest.
– “Stilts” walked beyond the nest.
• Conclusion:
– Desert ants use information on stride length and
number to calculate how far they are from the nest.

35. Elements of a Well-Designed Experiment
The experiment just described is well-designed:
1. It included a control group (the “normal” ants)
to check for other factors that might influence
the outcome.
2. Experimental conditions were controlled to
eliminate other variables.
3. The test was repeated to reduce the effects of
distortion due to small sample size.

36. The Principles of Experimental Design
Biologists practice evidence-based decision making. They
ask questions about how organisms work, pose
hypotheses to answer those questions, and use
experimental or observational evidence to decide which
hypotheses are correct.