darwin s two main contributions - wsu...

Darwin�s Two Main Contributions

•  Carried out the necessary research to conclusively document that evolution has occurred

•  Discovered the process by which complex, functional design originates in living things: natural selection

Charles Darwin (1809-1882)

Darwin�s Life •  Family

–  English –  moderately wealthy (mom was a

Wedgewood) –  Dad influenced his career options

•  Education –  Started in medicine at 16 –  Switched to theology at Cambridge –  Interested in the scientific ideas of

geologist Adam Sedgwick and naturalist John Henslow

–  At first, didn�t believe evolution occurred

–  Far more interested in biology than theology when he graduated

The Beagle •  Five-year voyage on the

H.M.S. Beagle (1831-1836) at age 22 with Captain Robert Fitzroy

•  Galapagos Islands

Darwin�s Influences

Charles Lyell (1797-1875): geologist who popularized �uniformitarianism� (vs. �catastrophism�


So, some individuals will reproduce, and others will not. Question: are �winners� a random selection, or do some individuals have an advantage over others? "The elephant is reckoned the slowest breeder of all known animals, and I have taken some pains to estimate its probable minimum rate of natural increase; it will be safest to assume that it begins breeding when 30 years old and goes on breeding until 90 years old; if this be so, after a period from 740 to 750 years there would be nearly 19 million elephants descended from this first pair.” (Darwin)

Thomas Malthus (1766-1834) was an economist who observed that more individuals are born than survive to reproduce; individuals are thus in a �struggle for existence,� that is, competition

•  One pair of mice is capable of producing a litter of six offspring as many as six times a year. Within six weeks, each offspring can produce litters of their own.



Artificial Selection

Darwin�s Influences Comparative Anatomy

Vertebrate forelimb


Fossils

Darwin�s Influences Geographic distribution of traits: beaks were well-adapted to

local environments on the islands

Adaptive Radiation in Galapagos Finches

Adaptive Radiation

•  Geology (Lyell) •  Within-species competition (Malthus) •  Artificial selection (breeders) •  Comparative anatomy •  Paleontology (fossils) •  Geographic distribution of traits (finches)


...Natural Selection

Darwin�s Short Definition

“I have called this principle, by which each slight variation [in a trait], if useful, is preserved, by the term Natural Selection.”

- From The Origin of Species

Natural Selection • Natural selection is the process by which favorable traits that are heritable become more common in successive generations of a population of reproducing organisms, and unfavorable traits that are heritable become less common.

• Over time, this process can result in adaptations that specialize organisms for particular ecological niches and may eventually result in the emergence of new species.

Natural Selection •  Assumption 1: Reproducing entities exist. •  Assumption 2: Variations exist, and they can be

passed on to offspring (heritable variation). •  Assumption 3: Variations have reproductive

consequences. •  Result: over time, the entire population will come

to possess the reproductively superior variation—adaptations.

•  One example: camoflauge

Reproducing entities exist.

Natural Selection, Redux

Variations exist, and they can be passed on to offspring (heritable variation).

Natural Selection

Variations have reproductive consequences.

Natural Selection

Over time, the entire population will come to possess the reproductively advantageous variation.

Natural Selection

After thousands of generations…adaptations Natural Selection

Adaptation here: camouflage

Darwin�s �Influences�

Alfred Russel Wallace (1823-1913)

Why did he wait so long to publish his theory of natural selection?

Darwin�s Biggest Scientific Problem

• Darwin realized that natural selection for specific traits could lead to changes in species through time.

• However, Darwin lacked information on how these traits were passed from generation to generation.

Genetics

Gregor Mendel (1822-1884)

Mendel was the first to explore the units of inheritance: genes.

What do GENES do?

They control the production specific PROTEINS in living

things… By stringing up small amino acid

molecules into long protein strands…

Genetics and Protein Synthesis;

Bodies are made of protein and other stuff…

Organisms� Components •  Organism = a living thing •  Generally all can be sorted into 5 (or 6) kingdoms: animals,

plants, fungi, bacteria, protists •  Materialism: living things are made of matter •  What kind of matter? Molecules…

–  Protein: the stuff living things are made of, e.g., collagen, enzymes, etc.); *there are some exceptions—take upper division biology classes if you are interested

–  Also made of: water, carbohydrates, fats, vitamins/minerals, DNA (nucleic acids), etc.

–  Proteins are long molecules that are folded over on themselves –  The components of protein molecules are smaller molecules called amino

acids (AAs)

Amino Acids

•  There are 20 kinds of AAs that make up all the proteins that organisms have –  Such as: alanine, asparagine, methionine…

– Made of Hydrogen, Oxygen, Nitrogen, Carbon, (HONC) and Sulfur (S only in methionine and cysteine)

Amino Acids •  AAs are small molecules, but when strung up and folded over on

themselves to form a protein, they can be quite large •  AAs are attached by peptide bonds

Amino acid �strand�

Each AA is like a bead on a necklace; electrochemical interactions among neighboring AAs cause the strand to fold over on itself in specific ways. The folded strand is a protein. Different AA sequences will make different proteins.

Protein

•  Proteins interact with other substances (including other proteins) in specific ways that are determined by their electrochemical properties.

•  There are only 20AAs out there—a finite number (though in actuality the story is more complex than this)

•  Different lengths and permutations of the AAs that make up AA strands can lead to countless varieties of proteins

Protein Functions •  Structural proteins (collagen in skin, keratin in hair

and nails, proteins that make up muscle tissue, etc.) •  Transport proteins (hemoglobin is a blood cell protein

that transports oxygen to body tissues) •  Enzymes: proteins that catalyze (speed up) chemical

reactions in the body •  Immune functions •  Signaling functions: E.g., neurons in your brain

communicate with each other; these neurons are proteins (and other substances)

Proteins

•  From where do organisms get the AAs needed for body maintenance and growth?

Food! •  Foods are typically living

(or formerly living) substances…

•  What substances are in our food?

Lichtenstein 1962 �Meat�

Organismic Components •  Organism = a living thing •  Protein: the stuff living things are made of •  Also water, carbohydrates, fats, vitamins/minerals,

DNA (nucleic acids), etc. •  Proteins are long molecules that folded over on

themselves •  The components of protein molecules are smaller

molecules called amino acids (AAs)

Proteins to AAs •  Organism A eats foreign protein that makes up organism B •  Organism A breaks Organism B proteins into AAs:

digestion •  Organism A�s DNA restrings raw AAs up into Organism A

proteins •  Organism A�s DNA = blueprints •  Organism B (then A�s AAs) = raw building blocks of

proteins

Amino Acids to Proteins

…genes

•  Genes determine what proteins get built from those raw AA molecules

•  Genes are protein-coding units of DNA •  You eat proteins of other living things, and break the

protein into amino acids; then, genes in your DNA re-string those amino acids into proteins that YOU need to survive and reproduce

•  What is DNA?

Genes Proteins

DNA •  Deoxyribonucleic acid •  A long molecule with a small number of constituent molecules •  Shape is a �double helix�—think of a ladder that is twisted

DNA •  A sugar-phosphate �backbone,� (I.e., the �sides� of the ladder), and �rungs” made up of paired nucleic acids

•  There are 4 nucleic acids: adenine (A), thymine (T), cytosine (C), and guanine (G) [don’t worry about uracil (U), for the purposes of this class

•  Note these are not AAs •  A only bonds to T •  C only bonds to G •  A-T and C-G bonds are weak •  Sugar-phosphate bonds are

strong •  Lots of �zipping� action

Genes to Proteins •  Protein synthesis •  An elegant process…brief whiteboard illustration •  (RNA, Uracil, ribosomes: do not worry about these for this class)

•  Upshot: the sequence of nucleotides in DNA determines the sequence of AAs in protein manufacture (nucleic acid sequence maps to AA sequence, but not one-to-one, and redundancy is built into the system)

•  In other words, your DNA determines what proteins get built out of the AAs that your body extracts from the foreign proteins you eat

Genes Proteins Bodies

DNA molecule

Protein

Cell parts, cells, and tissues

Amino acid molecules

Amino acid strand

Organ Body

+

•  Genes are protein-coding regions of an organism�s DNA •  (1) They direct protein synthesis •  (2) They ALSO �replicate,� or reproduce, over generations, as

they are passed from parents to offspring (offspring inherit their parents� genes) –  (a) in single-celled organisms, one �mother� (or �parental�)

cell�s genes double then divide and are passed on to two �daughter� (or �offspring�) cells (the parent cell no longer exists—its body�s proteins now make up the bodies of two offspring)

–  (b) in multicelled organisms, there are two kinds of cells: somatic cells and germ cells:

•  (i) somatic cells (such as human skin cells), live only as a part of the parental body; somatic cell genes build proteins for the parent�s body; reproduction of somatic cells involves gene replication, but the new cells remain a part of the parental body

•  (ii) germ cells (such as sperm and eggs) are housed in the parental body; then, at the time of reproduction, a germ cell leaves the parental body, anddevelops a new multicelled body of its own

•  THE point: only germ cell genes can make it into the next generation for multicelled organisms like humans

freshwater paramecium (single-celled)

red-tailed hawk (multicelluled)

Genes (DNA segments)

Reproduction in Single vs. Multi-celled Organisms

single-celled �mother�

½ of reproduced genes passed to each of two identical, single-celled �daughters�

multi-celled �mother�

*The somatic line cells ARE the germ line cells

Somatic line cells

Germ line cell

All genes reproduce by doubling

At reproduction, germ line cell leaves mother�s body and multiplies, creating new somatic cells for its daughter body, and, at some point, a subsequent germ line of cells that the daughter can transmit into the next generation; germ line = eggs and sperm in sexually-reproducing species Germ line cell…

multi-celled �daughter�

Genes vs. Alleles •  Genes: protein-coding regions of an

organism�s DNA •  Alleles: different forms of a gene at

a particular spot (�locus�) on the DNA; different allele sequences make slightly different versions of a protein, but ultimately different alleles ore more-or-less functionally similar

•  Here, the gene = eye pigment; with a few exceptions, we all have eye pigment, and the gene for this pigment is at the same spot on out DNA strand for every person

•  Allele = green eyes vs. blue eyes: even though we all have eye pigment protein, different people can have different versions of the eye pigment protein

white flowers=TGACCGATA purple flowers=TGACCGACA

Allele Frequencies •  Allele frequency = the proportions of different alleles

among all the individuals in a specific population (in this room, allele frequencies underlying eye color might be

different from frequencies in a Scandinavian population, which might have more blue and green eyes people, or a population living near the equator, which might have more brown eyed people)

•  Whiteboard exercise on allele frequencies of eye color in this class, in order to illustrate what evolution is…

Exercise: Eye Color Allele Frequencies

•  100 people in class (assume, for now, that human eye color is determined by a single gene with 3 possible alleles: brown, blue, and green)

–  60 people have brown eyes –  30 people have blue eyes –  10 people have green eyes

•  The current �generation� of our classroom population, G1, has the allele frequencies: 60% brown, 30% blue, and 10% green

•  Everyone has the opportunity to reproduce. Many of us do. The next generation�s allele frequencies are…


•  The allele frequencies in the next generation, G2, are… •  …again 60% brown, 30% blue, and 10% green •  This means that allele frequencies have NOT changed over

generations: evolution has NOT occurred from generation 1 to generation 2.

•  Now this 2nd generation has the opportunity to reproduce. Many do. The allele frequencies in the next generation, G3, are…


•  The next allele frequencies in G3 are… •  now 90% brown, 5% blue, and 5% green •  (they had been 60% brown, 30% blue, and 10% green in G2) •  This means that allele frequencies HAVE changed over

generations: evolution HAS occurred from G2 to G3.

•  Evolution is defined as a change in allele frequencies in a population over generations


•  G3 allele frequencies are 90% brown, 5% blue, and 5% green

•  Now this generation has the opportunity to reproduce. Many do. The next allele frequencies in the next generation, G4, are…

•  90% brown, 5% blue, 4% green, and 1% purple

•  This means that allele frequencies HAVE changed over generations: evolution HAS occurred between G3 and G4.

•  But where did this new purple allele come from?

Mutations! •  Where do new, different alleles come from? Mutations. •  Mutations are random mistakes in the molecular sequence of DNA,

which can lead to changes in proteins that get built •  A change in the DNA sequence of a gene will cause a change in the

protein that gets built –  ATGCAAAATCGG=green eye pigment protein –  ATGCAACATCGG=purple eye pigment protein

•  Origins of mutations include radiation (x-rays, solar rays, other cosmic rays, nuclear waste), various non-living substances (asbestos, cigarette smoke), living substances (viruses), unknown causes, etc.

•  Only heritable mutations are relevant to the evolutionary process because evolution is a process that occurs over generations

•  Not all mutations that occur in living things are heritable; there is an important difference in the heritability of mutations in multi-celled vs. single-celled organisms...

Heritability in Multi-celled Organisms

Germ line cell

•  Mutation must be in germ line of cells to be passed to offspring; only mutations in the germ line heritable, and thus subject to the process of evolution

•  Mutations in the somatic line can lead to new proteins (usually bad) being built in the maternal body (�cancer�), but these alleles are NOT passed to the next generation; they die with the mother�s body

Heritability in Single-celled Organisms

x"Somatic and germ line are the same, so all mutations in parent will be passed to offspring; that is, all mutations are heritable

X-ray radiation causes a mutation in this parental gene (green)

•  Heritable alleles are passed from parent to offspring over generations.

•  Evolution is change in allele frequencies in a population over generations.

•  Natural Selection is one type of evolution (there are 4…)

�Evolution�

Definitions and Types of Evolution

•  There are 4 causes of changes in the allele frequencies in a population over time: –  (1) Migration of individuals in or out of a population can cause the

allele frequencies to change (e.g., a bunch of red eyed people join our population in the next generation)

–  (2) Mutations can cause allele frequencies to change (e.g., one person�s child happens to be born with a mutated allele that produces purple eyes)

–  (3) Genetic drift occurs when a random event NOT related to one�s alleles alters the allele frequencies in a population (e.g., the 5 blue eyed people in our population happen to fall off a cliff, erasing all blue genes from the subsequent generation—and having blue eyes had NOTHING to do with falling)

–  (4) Natural selection…

•  Natural selection is change in allele frequencies in a population over generations due to the causal effects alleles have on reproduction

Natural Selection •  If reproducing entities exist, if variations are heritable, and if

variations have reproductive consequences, then over time, the entire population will come to possess the reproductively superior variation –  *note that for multicelled organisms, these variations are in the germ

line of cells

•  In terms of genetics: Over generations, alleles that build proteins that promote their own reproduction relative to the rest of the alleles in the population will reproduce more than the population’s alleles that build proteins that hinder their own reproduction.

Within- and Between-Species Competition

•  A common misconception when thinking about natural selection

•  Competition or a struggle for existence among members of different species

–  (misconceptions of �Survival of the Fittest� notions…)

•  E.g., thinking about rabbits vs. foxes (thought experiment—then why are there still any rabbits around?...)

•  Or thinking about a species vs. the many environmental circumstances that it encounters, including other species

Not just getting food from the environment...

Getting more food than other members of your species from it

Not just avoiding predators…

Avoiding predators better than other members of your species

Parasitic micro-organisms: roundworm, protozoan, bacterium, fungus, yeast

Not just avoiding parasites…

Avoiding parasites better than other members of your species do (mange; a funny website: http://www.giantmicrobes.com/)

Wedge tail eagle nest

Not just getting good living spaces...

Getting better living spaces than other members of your species (�strumming,� Riechert & Hammerstein)

Funnel spider

Stay Away from Funnel Spiders

Don�t think of it as the environment (which includes other species) vs. the mouse

Think of it as mouse vs. mouse in a particular environment (which includes other species and

also NONliving things!)

No place to live. No food. Couldn�t find a mate. Predator ate him. Did not reproduce. His nonexistent kids did not inherit his genes and the traits those genes build.

Found place to live. Out-competed other mice for food. Found a mate. Successfully avoided predators. Reproduced successfully. His kids inherited his genes and the traits those genes build.

•  In any population, not all individuals survive to reproduce.

Mouse vs. mouse

Male red deer

Important for mammals, and highlights the importance of within-species competition to exist and to reproduce: getting more or better mates

than other same-sexed members of your species

Within-species Competition: The Bear and the Campers

A final point re. intro to genetics and natural selection: mutations

•  From where do these heritable variations originate?

•  Mutations. •  What are mutations?

–  Nucleotide substitutions (an AGT or C gets replaced by the �wrong letter�)

•  The impact of mutations when they are on somatic-line cells vs. germ lines

•  Mutations impact evolution in different ways based on what types of cells they are in; for multicalled organisms:

–  Somatic cell = maybe cancer—bad for survival, but questionably bad; and may or may not impact reproduction…or not cancer (thus irrelevant to survival/reproduction)

–  Germ line = Potentially very important to reproduction (not survival) and the physical process of Natural Selection (examples?)…

darwin s two main contributions - wsu...

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