4. Chapter 3: Charles Darwin & Evolution

Question 1

Describe Darwin’s voyage.

Answer 1

Darwin leaves the Beagle, a ship commissioned by the British government to do the cartography of the coast of South America. Darwin took a crash course in cartography becoming the naturalist of the voyage. Darwin studied geology of South America collecting samples of fauna and flora (preserving animals+plants). During the voyage, two books had an impact on Darwin William Paley’s “Theology, or evidences of the existence and attributes of the deity” who was the father of the theology of nature advocating that harmony and design in nature are indicators of the existence and the acts of God which is defined today as intelligent design. The second book was Lyell’s “Principle of Geology” where at the start of the expedition he believed in the Great Flood and in Cuvier’s catastrophism (protestant beliefs) and returned to be in total agreement with Lyell and Hutton’s principle of uniformity. Darwin then published a memoir on his adventures which became a bestseller starting his fame.

Question 2

What did Darwin question about South American fauna?

Answer 2

• FEW SPECIES IN COMMON
• CLIMATE ZONE≠SIMILAR
• REGIONAL ZONE=SIMILAR
• REGIONAL FOSSILS=CURRENT

▪ Why do the fauna and flora of Africa, Europe, Australia and South America
▪ Why are the animals and plants of the temperate zones of South America
have relatively few species in common? the species in temperate Europe?
resemble the species living in the tropical zones of South America but not
▪ Why are the mammal fossils of South America absent from the current
fauna (e.g. Giant Sloth)? Why do these fossils show resemblance with
current species found only in South America (e.g. Three-toed Sloth)?

Question 3

What did Darwin observe in the Galapagos Island?

Provide four examples of his observations.

Answer 3

-UNIQUE FAUNA
-RESEMBLES AMERICAS
-MORPHOLOGICAL VARIABILITY
Ie. Galapagos Marine Iguana are the only iguanas to live in a marine environment which is unique to the Galápagos Islands and the Galápagos sea lions are closely related to the Californian sea lion. Galapagos tortoise have 15 different subspecies (shell variability). Galapagos finches have morphological variability in terms of their beak (bird beaks for cactus or insects or seeds). Why? They show morphological similarities because they share a common ancestor linking them to South America. One can only assume how these species got to the Galápagos Islands.
▪ Why does it show resemblance with species on the American continent?
▪ The fauna on the Islands is unique. Why?

Question 4

What inspired Darwin’s theory on natural selection?

Answer 4

Thomas Malthus’s “An essay on the principle of population” where he wrote that every human population has a tendency to increase geometrically (exponentially) whereas the available resources to feed these populations increase arithmetically (linear). Thus, the human population increases faster than its capacity to feed itself leading to a crisis point in which a chaos of famine/hunger/strike/war/sickness occurs and eventually to a substantially reduced population size. The scenario is a winner loser situation where the losers have no food, unable to reproduce and die.

Question 5

What were Darwin’s observations?

Answer 5

1. All species can produce more offspring than their environment can sustain and many of these offspring fail to survive and reproduce (ie. samaras of a maple tree, spore clouds from a puffball mushroom, ocean sunfish’s hundreds of millions of eggs)
2. Members of a population often vary in their inherited traits. (Dots from the Asian ladybird beetle and the shell colour of amphidromus adamsii)

Question 6

What is natural selection? What are its inferences?

Answer 6

Natural selection enables the emergence of adaptations. They infer that:

1. Individuals whose inherited traits gives them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals
2. In generational shifts there is an unequal capacity of survive and reproduce called a differential reproductive success which results in an accumulation of favourable traits in a population essentially greater proportion and frequency will increased of a certain phenotype/genotype limiting genetic variability

Question 7

What are important notions linked with natural selection?

Answer 7

1.Individuals do not evolve only populations evolve
(Individuals are only carriers of gene) (Lamarckism: individual ≠Darwin: population)
2. Only hereditary traits are subjects to natural selection
3. Genetic variability is needed for evolution to occur
4. Natural selection corresponds to differential reproductive success within a population from generation to generation (change in frequency of genotype)
5. With time, natural selection enables individuals to become better adapted to their environment
6. Environmental factors vary in time and space thus the selective forces are variable (summer vs winter, white-tail deers in Ontario+Quebec vs Costa Rica)
7. Traits in populations will change and can modify the species (change in morphology ie use of utensils means less pressure on our jaws thus they are becoming smaller)

Question 8

How does Darwin comprehend resemblance of species? (How/why does that lead him to search for the idea of natural evolution)

Answer 8

Darwin comprehended resemblance of species through phylogenetic trees that species show resemblance to each other because they share a common ancestor not a common environment. Darwin’s phylogenetic terres confirmed what he knew through observation but not yet the mechanism of evolution. Darwin rejects Lamarck’s evolutionary mechanism of environmental determinism. Darwin rejects the fixity (no change) of species and accepts the concept of descent with modifications (evolution). Darwin also begins to have a very materialistic view of life that is in contradiction to the religious dogma of the time. This leads him to begin the search for an evolutionary mechanism.

Question 9

Why/What did Darwin publish in his findings?

Answer 9

Darwin was pressured into publishing his ideas through friends and a letter by Alfred Wallace who had also come to the same conclusions as Darwin concerning the theory of natural selection by observing the fauna of Indonesia. Darwin publicly released his views on the evolution of species through the book “On the Origin of Species” which became an instant bestseller and caused great controversy. Darwin’s theory has never been refuted and Darwin had included a chapter dedicated to the most important arguments against his theory.

Question 10

How did Darwin justify the mechanism of natural selection as valid?

(What is differential reproductive success)

Answer 10

1. Natural selection respects the principle of uniformity of Lyell and Hutton
2. The results of natural selection are visible in nature
3. Natural selection can be verified on current populations through artificial selection
4. It is a materialistic concept (no need for divine intervention) because of two things, that:
   a. Natural selection is not a random process and it enables individuals that are better adapted to their environment to become more abundant in the population than those who are not which is the idea of differential reproductive success
   b. Natural selection is not a quest for perfection, evolution is not a directed process. It does not lead to the appearance of “perfect” traits. Organisms only adapt to their environment, some become more abundant in an environment or some traits are selected due to a predation factor ONLY TO ADAPT & SURVIVE

Question 11

What is the difference between artificial selection and natural selection?

Answer 11

Artificial selection is finalized because the goal/objective, is fixed well in advance, precedes the causes. The end result can be obtained in a few generations. Natural selection is not finalized. It can take a long time for changes to occur (geological time scale).

Question 12

Provide an example of artificial selection

Answer 12

Our food is artificially selected. A wild mustard plant that is artificially selected leaves is kale, for its flowers and stems is broccoli, for apical bud is cabbage, for auxiliary buds is Brussels sprouts.
Mop dog, length of coat has genetic basis so breeding with long coated dogs to achieve mop dog

Question 13

Provide 3 examples of natural selection?

Answer 13

1. Humans: adaptation to altitude in:
   a. Andes: mutation for increase in hemoglobin concentration
   b. Tibet Plateau: mutation (involving multiple genes) deeper breath, larger pulmonary capacity and increased blood flow
   : genetically favoured in Plateau, as the abundance of individuals withstanding (genetic traits allowing for survival and reproduction in) high altitudes increased through time as they had differential mortality and reproductive rates
2. Medium Ground Finches: Climate (drought) in Daphne Major Galápagos Islands substantially decreased population because selection favoured individuals that had bigger and stronger beaks to break Available seeds during drought thus lowered abundance from small-beaked birds as limited reproduction and many died.
3. Moths: selected in way of feeding. Dark morphs were more frequent on soot-infested trees (urban) while grey morphs were more frequent in countryside because of lighter coloured trees and predators were attracted to eating more vibrant food as it also easier to see (black/grey hereditary trait helped them camouflage depending on tree colour)

Question 14

What do all cases of natural selection provide?

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Answer 14

Natural selection provides the hereditary traits that give a reproductive advantage to individuals in a population will be favoured. Thus from generation to generation there will be a higher percentage of individuals carrying the adaptation. That is natural selection, Darwin’s descent with modification, evolution. These adaptations can sometimes redefine a species and define a new species (rarely ever).

Question 15

How are homologous structures explained na what are they?

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Answer 15

Homologous structures are explained by the descent with modification theory (theory of evolution) that resemblance between certain traits even if function is different (the reality of evolution).
A homologous structure is the same feature but different fate so different function but commonly evolved.

Question 16

What are examples of homologous structures?

Answer 16

We can observe in embryos (chicken, human,..) the presence of pharyngeal pouches (which disappear in humans after a few weeks) and post anal tails which are found in all vertebrates (which in humans remains as our coccyx).

Question 17

Phylogeny tree diagrams are based on..

Answer 17

Phylogeny tree diagrams are based on.. ..homologous structures
Each common ancestor defines its species for example a common ancestor with digit bearing limbs categorizes tetrapods by the presence of their digits, ancestor with feathers defines birds but the presence of feathers, and so on.

Question 18

What approaches of evolution are there and why is one type wrong? Give horse example.

Answer 18

There is the classic interpretation which presents evolution in a linear way and there is the more realistic approach which presents evolution as a phylogenetic tree. The classic interpretation is wrong because it is oversimplified and gives the wrong assumption when in reality evolution is much more complex in terms of morphology which is lost in linear story as well it does not allow the idea that different species lived at the same time at one point.
For example, horses did not just evolve into larger horses. There are two types of horses forest dweller which are browser and ate leaves so there was no selective pressure which is why they are a smaller species while prairie dwellers are grazer meaning that when they eat grass sand would also enter so they had selective pressure to chew which explains the presence of their larger teeth.

Question 19

Where can we understand where species come from (and how can we properly categorize them). Give example (of whale).

Answer 19

Fossils provide key information to fill in important gaps in morphological differences and variability because 99% of species from earth are extinct and only 1% of species are living today, so most evolutionary branches finish in extinction. Through fossils we can understand that the pakicetus, whale and hippo share a common ancestor.

Question 20

What is a vestigial structure and provide examples.

Answer 20

A vestigial structure is an anatomical structure that is present yet has lost almost all of its initial function, and they are proof of evolution as they are remnants of what was once fully functioning in a an ancestor.
Examples:
1. Third Eyelid/ Nictitating membrane: no reason to have has no function, just sits there
2. Appendix: an ancestor had a fully functioning caecum and our small appendix is remnant of that, no longer need large digestive system because of introduction of meats into our diet no pressure to digest cellulose (plants)
3. Goosebumps and hair: no reason to have muscle associated with contracting every hair follicle nor do we have any hair density to help us retain heat
*4. Hiccups: is a very light pinch on phrenic nerves which contracts the epiglottis and diaphragm this is where our nerve followed the evolutionary pattern of fishes because fishes’ movement of their gills is associated with the phrenic nerve.

Question 21

What would be sufficient to refute the whole concept of evolution?

Answer 21

The discovery of a fossil in the wrong place in the geological archives.