Download Outcomes of Natural Selection (Chapter 19)

Natural Selection and Speciation
(Chapter 19 and 20)
Small Steps or Great Leaps?
• Gradualism is the slow change from one form to
another
• punctuated equilibrium- instead of a slow,
continuous movement, evolution tends to be
characterized by long periods of virtual standstill
(equilibrium or stasis), "punctuated" by episodes
of very fast development of new forms
punctuated equilibrium site
Random Changes in Frequencies
• a change in a population due simply to chance is
called genetic drift
– results in a population losing genetic variation
• Processes leading to genetic drift:
1. population bottleneck – a population
becomes reduced quickly producing a
random change in gene frequencies
• the allele frequency of the “new
population” would depend the surviving
organisms’ alleles
– Tule elk of California in text
– Northern elephant seals
» 20 seals in 1890, now 30,000
2. founder effect – few individuals stray and
establish a new colony, in a new habitat, and
therefore a new population with diff. freq.
than the original pop. (Fig. 19.8 in text)
• Afrikaners of South Africa in text
– In the 1680s Ariaantje and Gerrit Jansz emigrated from Holland to
South Africa, one of them bringing along an allele for the mild
metabolic disease porphyria. Today more than 30000 South Africans
carry this allele and, in every case examined, can trace it back to this
couple — a remarkable example of the founder effect.
• Amish in Pennsylvania
– Eastern Pennsylvania is home to beautiful farmlands and countryside,
but it's also a gold mine of information for geneticists, who have
studied the region's Amish culture for decades. Because of their closed
population stemming from a small number of German immigrants -about 200 individuals -- the Amish carry unusual concentrations of
gene mutations that cause a number of otherwise rare inherited
disorders, including forms of dwarfism and plolydactyly.
Species (Latin for “appearance”)
Experimental results: The first steps of
speciation have been produced in several
laboratory experiments involving "geographic"
isolation. For example, Diane Dodd took fruit
flies from a single population and divided them
into separate populations living in different
cages to simulate geographic isolation. Half of
the populations lived on maltose-based food, and
the other populations lived on starch-based
foods. After many generations, the flies were
tested to see which flies they preferred to mate
with. Dodd found that some reproductive
isolation had occurred as a result of the
geographic isolation and selection in the
different environments: "maltose flies" preferred
other "maltose flies," and "starch flies" preferred
other "starch flies." Although, we can't be sure,
these preference differences probably existed
because selection for using different food
sources also affected certain genes involved in
reproductive behavior. This is the sort of result
we'd expect, if allopatric speciation were a
typical mode of speciation.
• morphological definition - type of living
organism with fixed characteristics that
distinguish it from other species
– useful but doesn’t recognize that species
evolve and may not be able to interbreed
• biological definition – a reproductively
isolated group of actually or potentially
interbreeding populations having a
common gene pool that produce fertile
offspring
Problems with defining a species
• many different species can interbreed
– ex. dogs/dingos/wolves/coyotes/PLANTS
• fossils can’t be classified according to the
biological definition
• some species reproduce asexually
• species that are geographically close to
each other can breed but those far apart
can’t
Classifying/Naming Species
Systematics – the science of determining
evolutionary relationships among organisms
Taxonomy – the science of identifying, naming,
and classifying organisms
Both deal with determining how to classify an
organism
• Use the binomial system consisting of genus and
species to name the organism
– started by Carolus Linnaeus
• normally use Latin names, names of people, or
regions organism found
Carl Linnaeus, also known as Carl von Linné or Carolus Linnaeus, is
often called the Father of Taxonomy. His system for naming, ranking,
and classifying organisms is still in wide use today (with many
changes). His ideas on classification have influenced generations of
biologists during and after his own lifetime, even those opposed to the
philosophical and theological roots of his work.
• Hierarchy of the taxa (also can have prefix super or sub
in most taxa)
– Kingdom (Monera, Protista, Fungi, Plantae, Animalia)
– Phylum
– Class
– Order
– Family
– Genus (capitalize & underline or italics)
– Species (underline or italics)
• the hierarchy of names also defines the phylogeny
(evolutionary history of an organism)
– for example, two species in the same class should
share more ancestry (more closely related) than
two species in different classes
•Kids Playing Chicken On Freeways Get Smashed.
•King Phillip called out for good soup.
•King Philip came over from Germany swimming.
•King Philip came over for good spaghetti.
•King Philip came over for good sex.
•Kings play chess on fat green stools.
•Kings play chess on fine gold steps.
•Kings play cards on fairly good soft velvet. (with "v" standing for
"variety")
•Kings possess crowns of fine gem stones.
•Kenneth, please close our front gate soon.
•Keep plates clean or family gets sick.
•Killing people causes outbursts from general society.
•Klingon phasers charge on fast gray ships.
•Keep putting condoms on for good sex.
•King pine cones often form great saplings