Download "Lamarck" is now associated with a discredited view of

Article 1: Jean Baptiste Lamarck vs. Darwin
Although the name "Lamarck" is now associated with a discredited view of evolution, the French biologist's notion
that organisms inherit the traits acquired during their parents' lifetime had common sense on its side. In fact, the
"inheritance of acquired characters" continued to have supporters well into the 20th century.
Jean Baptiste Lamarck (1744-1829) is one of the best-known early evolutionists. Unlike Darwin, Lamarck believed that
living things evolved in a continuously upward direction, from dead matter, through simple to more complex forms, toward
human "perfection." Species didn't die out in extinctions, Lamarck claimed. Instead, they changed into other species.
Since simple organisms exist alongside complex "advanced" animals today, Lamarck thought they must be continually
created by spontaneous generation.
According to Lamarck, organisms altered their behavior in response to environmental change. Their changed behavior, in
turn, modified their organs, and their offspring inherited those "improved" structures. For example, giraffes developed their
elongated necks and front legs by generations of browsing on high tree leaves. The exercise of stretching up to the leaves
altered the neck and legs, and their offspring inherited these acquired characteristics.
According to Darwin's theory, giraffes that happened to have slightly longer necks and limbs would have a better chance
of securing food and thus be able to have more offspring -- the "select" who survive.
Conversely, in Lamarck's view, a structure or organ would shrink or disappear if used less or not at all. Driven by these
heritable modifications, all organisms would become adapted to their environments as those environments changed.
Unlike Darwin, Lamarck held that evolution was a constant process of striving toward greater complexity and perfection.
Even though this belief eventually gave way to Darwin's theory of natural selection acting on random variation, Lamarck is
credited with helping put evolution on the map and with acknowledging that the environment plays a role in shaping the
species that live in it.
Questions:
1. What was Lamarck’s theory of evolution?
2. What was Darwin’s theory of evolution?
3. In your own words: How did Darwin’s and Lamarck’s ideas about evolution differ?
Article 2: A Mutation Story:
A gene known as HbS was the center of a medical and evolutionary detective story that began in the middle
1940s in Africa. Doctors noticed that patients who had sickle cell anemia, a serious hereditary blood disease, were more
likely to survive malaria, a disease which kills some 1.2 million people every year. What was puzzling was why sickle cell
anemia was so prevalent in some African populations.
How could a "bad" gene -- the mutation that causes the sometimes lethal sickle cell disease -- also be beneficial? On the
other hand, if it didn't provide some survival advantage, why had the sickle gene persisted in such a high frequency in the
populations that had it?
The sickle cell mutation is a like a typographical error in the DNA code of the gene that tells the body how to make a form
of hemoglobin (Hb), the oxygen-carrying molecule in our blood. Every person has two copies of the hemoglobin gene.
Usually, both genes make a normal hemoglobin protein. When someone inherits two mutant copies of the hemoglobin
gene, the abnormal form of the hemoglobin protein causes the red blood cells to lose oxygen and warp into a sickle shape
during periods of high activity. These sickled cells become stuck in small blood vessels, causing a "crisis" of pain, fever,
swelling, and tissue damage that can lead to death. This is sickle cell anemia.
But it takes two copies of the mutant gene, one from each parent, to give someone the full-blown disease. Many people
have just one copy, the other being normal. Those who carry the sickle cell trait do not suffer nearly as severely from the
disease.
Researchers found that the sickle cell gene is especially prevalent in areas of Africa hard-hit by malaria. In some regions,
as much as 40 percent of the population carries at least one HbS gene.
It turns out that, in these areas, HbS carriers have been naturally selected, because the trait confers some resistance to
malaria. Their red blood cells, containing some abnormal hemoglobin, tend to sickle when they are infected by the malaria
parasite. Those infected cells flow through the spleen, which culls them out because of their sickle shape -- and the
parasite is eliminated along with them.
Scientists believe the sickle cell gene appeared and disappeared in the population several times, but became
permanently established after a particularly vicious form of malaria jumped from animals to humans in Asia, the Middle
East, and Africa.
In areas where the sickle cell gene is common, the immunity conferred has become a selective advantage. Unfortunately,
it is also a disadvantage because the chances of being born with sickle cell anemia are relatively high.
For parents who each carry the sickle cell trait, the chance that their child will also have the trait -- and be immune to
malaria -- is 50 percent. There is a 25 percent chance that the child will have neither sickle cell anemia nor the trait which
enables immunity to malaria. Finally, the chances that their child will have two copies of the gene, and therefore sickle cell
anemia, is also 25 percent. This situation is a stark example of genetic compromise, or an evolutionary "trade-off."
Questions:
1. What is the HbS gene?
2. Why were the carriers of the HbS gene selected for (what is the advantage) ?
3. So, what is the evolutionary tradeoff?
4. Do the punnet square for two carriers of the HbS gene
Article 3: Shape of Trees: Frustration Principle:
Those gadgets at the hardware store advertised as "10 tools in one" have their place -- when packing for a
camping trip, for example -- but none of the components will do its job as well a single knife, screwdriver, or pliers would
perform it. It seems to be a law that the more tasks an implement is asked to take on, the worse it does any of them.
Looking at nature, scientists have discovered the same trade-off between versatility and performance when the organs of
living things have evolved to do more than one job. In fact, a body structure that creates a survival advantage in some
situations may be downright harmful in other environments. That explains why some disadvantageous traits haven't been
eliminated by natural selection and instead persist.
Scientists invoke the "principle of frustration" in these cases. All organisms are under a variety of selection pressures at
once, and they evolve structures or behavior that inevitably are compromise solutions to the conflicting needs. Sometimes
there are several such solutions successful enough to give a survival edge.
One recent experiment used computer simulations to show how the principle of frustration can cause the evolution of
several solutions. Karl Niklas, a scientist at Cornell University, started with the forms of the earliest known land plants. He
let them evolve along several paths, aimed at adapting to different selection pressures. One was reproductive success,
and these plants would need many seeds as high off the ground as possible. For harvesting light, the production of many
non-overlapping horizontal branches would be the best solution. For stability and strength, the trees would need a limited
number of branches and few long, horizontal ones.
In each of these cases where only one selective force played on the plants' evolution, they developed very different
solutions. But then Niklas did a simulation with all three pressures operating at once. The result? A much greater range of
equally optimal compromises, and many of them looked a lot like trees we're familiar with today
Questions:
1. Why haven’t disadvantageous traits in a certain environment been eliminated from a population over time?
2. Describe the principle of frustration using the computer example from the article
Article 4: Genetic Drift and the Founder Effect:
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.
One form of dwarfism, Ellis-van Creveld syndrome, involves not only short stature but polydactyly (extra fingers or toes),
abnormalities of the nails and teeth, and, in about half of individuals, a hole between the two upper chambers of the heart.
The syndrome is common in the Amish because of the "founder effect."
When a small part of a population moves to a new locale, or when the population is reduced to a small size because of
some environmental change, the genes of the "founders" of the new society are disproportionately frequent in the
resulting population.
If individuals in the group tend to marry within it, there's a greater likelihood that the recessive genes of the founders will
come together in the cells that produce offspring. Thus diseases of recessive genes, which require two copies of the gene
to cause the disease, will show up more frequently than they would if the population married outside the group.
In the Amish, in fact, Ellis-van Creveld syndrome has been traced back to one couple, Samuel King and his wife, who
came to the area in 1744. The mutated gene that causes the syndrome was passed along from the Kings and their
offspring, and today it is many times more common in the Amish population than in the American population at large.
The founder effect is an extreme example of "genetic drift." Genes occurring at a certain frequency in the larger population
will occur at a different frequency -- more or less often -- in a smaller subset of that population. As in the example of
human diseases, genetically determined traits that would ordinarily be uncommon in the overall gene pool might crop up
with distressing frequency in a small subset of that pool.
Questions:
1. What is the founder effect (in your own words)?
2. What has happened to the Amish people genetically because of the founder effect?
3. What is genetic drift in your own words?
Article 5: Biogeography: Polar Bear and Penguins:
Darwin, Wallace and the other 19th century naturalists who traveled widely were fascinated by the distribution of
animals and plants in their habitats around the world. Why do the Galapagos Islands of South America and the Cape
Verde Islands off Africa have strikingly different fauna and flora, despite having similar environments? Why does the Arctic
have polar bears and Antarctica penguins?
These patterns impressed Darwin deeply. To him, they argued that species arose in single centers by descent with
modification from existing species, and that their geographic range was limited by their ability to migrate to other suitable
environments.
The distribution of flora and fauna of the oceanic islands provided Darwin with some of his strongest arguments. The
islands contain a small number of species because immigration from the mainland was difficult, he said. Some categories
of life are absent altogether, such as batrachians -- frogs, toads, and newts -- even though they would seem to be
adapted for such habitats. The reason? They are killed by saltwater, so could not reach the islands by migration.
Terrestrial mammals aren't found on oceanic islands more than 300 miles from the mainland. But bats, with their longdistance flying ability, are plentiful.
Another point: Most of the species on islands, while distinct from other species, are most closely related to species on the
nearest mainland. Therefore, Darwin said, the island inhabitants must have migrated from the original, mainland area
where the species originated. That explains why the species on the Galapagos Islands most closely resemble those on
the nearby South American mainland, and those in the Cape Verdes resemble those of west Africa.
Aside from the islands, Darwin was intrigued by unusual distributions of animals and plants across the continents. He
concluded that changes in locations of climatic zones over time -- the advance and retreat of glaciers, for example -- could
explain some of the patterns in animals' habitats.
Just as intriguing to Darwin, and even more apparent now, is the fact that fossils of possible ancestors of living species
are often found in the same parts of the globe where their descendants live today. Darwin observed this in the South
American fossils he collected, relatives of today's capybaras and armadillos. Apes today live only in Africa and Asia, and
that is where the fossils most resembling modern apes are also found. There are no apes, fossil or living, known from
anywhere in the Americas.
These same patterns are just as impressive today. And since Darwin's day, advances in scientific understanding have
shown how accurate his conclusions were. For example, plate tectonics, undreamed of when Darwin was forming his
ideas, fits elegantly into Darwin's theory as another major influence on dispersal, helping to produce the patterns in the
distribution of both fossils and living organisms seen around the world in modern times.
Questions:
1. What is the contradiction that Darwin and other evolutionary biologists noticed?
2. How did Darwin explain the existence of this contradictions? Give at least 3 reasons.