Chapter 1 - What is Evolution?

Question 1

William Paley

Answer 1

• English philosopher
• If we came across a watch lying on the ground, he said, we would certainly recognize it as the work of a watchmaker. Likewise, the existence of well-adapted organisms and their intricate features surely implied a conscious, celestial designer—God

Question 2

Charles Robert Darwin (1809 - 1882)

Answer 2

• A keen naturalist
• Originally studied to be a minister at Cambridge University
• Looked beyond the obvious
• Suggested (& supported with copious evidence) 2 ideas that forever dispelled the idea of deliberate design
• He was not the first to think of evolution, many before him (including his grandfather Erasmus) thought of it too
• Darwin was the first to use data from nature to convince people that evolution was true

Question 3

Darwin’s 2 ideas

Answer 3

1. Evolution

2. Natural Selection

Question 4

Modern theory of evolution

Answer 4

Life on Earth evolved gradually beginning with one primitive species—perhaps a self- replicating molecule—that lived more than 3.5 billion years ago; it then branched out over time, throwing off many new and diverse species; and the mechanism for most (but not all) of evolutionary change is natural selection

Question 5

The 6 components of the modern theory of evolution

Answer 5

1. Evolution
2. Gradualism
3. Speciation
4. Common ancestry
5. Natural selection
6. Nonselective mechanisms of evolutionary change

Question 6

1. Evolution

Answer 6

• Evolution means that a species undergoes genetic change over time.
  That is, over many generations a species can evolve into something quite different, & those differences are based on changes in the DNA, which originate as mutations.
• The species of animals and plants living today weren’t around in the past, but are descended from those that lived earlier.
• Although ALL species evolve, they don’t do so at the same rate.
• The theory of evolution does not predict that species will constantly be evolving, or how fast they’ll change when they do.
  That depends on the evolutionary pressures they experience.
• Some, like horseshoe crabs and gingko trees, have barely changed over millions of years.

Question 7

2. Gradualism

Answer 7

• It takes many generations to produce a substantial evolutionary change, such as the evolution of birds from reptiles
• Gradualism does not mean that each species evolves at an even pace
• When natural selection is strong, as when an animal or plant colonizes a new environment, evolutionary change can be fast.
  Once a species becomes well adapted to a stable habitat, evolution often slows down.

Question 8

3. Speciation

Answer 8

• It is a remarkable fact that while there are many living species, we all share some fundamental traits
• Such as the biochemical pathways that we use to produce energy, our standard four-letter DNA code, and how that code is read and translated into proteins.
• This tells us that every species goes back to a single common ancestor, an ancestor who had those common traits and passed them on to its descendants.
• But if evolution meant only gradual genetic change within a species, we’d have only one species today—a single highly evolved descendant of the first species.
• Yet we have many: well over ten million species inhabit our planet today, and we know of a further quarter million as fossils. Life is diverse.
• How does this diversity arise from one ancestral form? This requires the third idea of evolution: that of splitting, or, more accurately, speciation.
• Speciation simply means the evolution of different groups that can’t interbreed—that is, groups that can’t exchange genes
• But species don’t have to split.
• Whether they do depends on whether circumstances allow populations to evolve enough differences that they are no longer able to interbreed.
• The vast majority of species—more than 99 percent of them—go extinct without leaving any descendants.
• Others, like gingko trees, live millions of years without pro- ducing many new species.
• Speciation doesn’t happen very often. But each time one species splits into two, it doubles the number of opportunities for future speciation, so the number of species can rise exponentially
• Speciation was so important to Darwin that he made it the title of his most famous book.

(read more on page 6)

Question 9

4. Common ancestry

Answer 9

• It stands to reason that if the history of life forms a tree, with all species originating from a single trunk, then one can find a common origin for every pair of twigs (existing species) by tracing each twig back through its branches until they intersect at the branch they have in common.
• This node, as we’ve seen, is their common ancestor.
• And if life began with one species and split into millions of descendant species through a branching process, it follows that every pair of species shares a common ancestor sometime in the past.
• Closely related species, like closely related people, had a common ancestor that lived fairly recently, while the common ancestor of more distantly related species, like that of distant human relatives, lived farther back in the past.
• Thus, the idea of common ancestry—the fourth tenet of Darwinism—is the flip side of speciation.
• It simply means that we can always look back in time, using either DNA sequences or fossils, and find descendant lineages fusing at their ancestors.
• The idea of common ancestry leads naturally to powerful and testable predictions about evolution.
• If we see that birds and reptiles group together based on their features and DNA sequences, we can predict that we should find common ancestors of birds and reptiles in the fossil record. Such predictions have been fulfilled, giving some of the strongest evidence for evolution.

Question 10

Common ancestry & Carl Linnaeus

Answer 10

• Actually, the nested arrangement of life was recognized long before Darwin.
• Starting with the Swedish botanist Carl Linnaeus in 1635.
• Biologists began classifying animals and plants, discovering that they consistently fell into what was called a “natural” classification.
• Strikingly, different biologists came up with nearly identical groupings.
• This means that these groupings are not subjective artifacts of a human need to classify, but that they tell us something real and fundamental about nature.
• But nobody knew what that something was until Darwin came along, and showed that the nested arrangement of life is precisely what evolution predicts.
• Until about thirty years ago, biologists used visible features like anatomy and mode of reproduction to reconstruct the ancestry of living species.
• This was based on the reasonable assumption that organisms with similar features also have similar genes, and thus are more closely related.
• But now we have a powerful new and independent way to establish ancestry: we can look directly at the genes themselves.
• By sequencing the DNA of various species and measuring how similar these sequences are, we can reconstruct their evolutionary relationships.

Question 11

5. Natural Selection

Answer 11

• The fifth part of evolutionary theory is what Darwin clearly saw as his greatest intellectual achievement: the idea of natural selection.
• Natural selection is both revolutionary and disturbing for the same reason: it explains apparent design in nature by a purely materialistic process that doesn’t require creation or guidance by supernatural forces.
• If individuals within a species differ genetically from one another, and some of those differences affect an individual’s ability to survive and reproduce in its environment, then in the next generation the “good” genes that lead to higher survival and reproduction will have relatively more copies than the “not so good” genes.
• Over time, the population will gradually become more and more suited to its environment as helpful mutations arise and spread through the population, while deleterious ones are weeded out.
• Ultimately, this process produces organisms that are well adapted to their habitats and way of life.
• The process is remarkably simple. It requires only that individuals of a species vary genetically in their ability to survive and reproduce in their environment. Given this, natural selection—and evolution—are inevitable.
• Natural selection can, over eons, sculpt an animal or plant into something that looks designed.
• Natural selection is not a master engineer, but a tinkerer.
• It doesn’t produce the absolute perfection achievable by a designer starting from scratch, but merely the best it can do with what it has to work with.
• Mutations for a perfect design may not arise because they are simply too rare.

Eg. Every instance of a plant or animal that is parasitized or diseased represents a failure to adapt.

Question 12

Alfred Russel Wallace & Natural Selection

Answer 12

• The idea of natural selection was not in fact unique to Darwin
• His contemporary, the naturalist Alfred Russel Wallace, came up with it at about the same time.
  Leading to one of the most famous simultaneous discoveries in the history of science.
• Darwin gets most of credit because in The Origin he worked out the idea of selection in great detail, gave evidence for it, and explored its many consequences.

Question 13

Mutations & Natural Selection

Answer 13

• Mutations are changes in traits that already exist; they almost never create brand-new features.
• This means that evolution must build a new species starting with the design of its ancestors.
• Evolution is like an architect who cannot design a building from scratch, but must build every new structure by adapting a preexisting building, keeping the structure habitable all the while. This leads to some compromises.

Question 14

6. Processes other than natural selection that can cause evolutionary change

Answer 14

• Natural selection does not yield perfection—only improvements over what came before.
• It produces the fitter, not the fittest.
• The most important is simple random changes in the proportion of genes caused by the fact that different families have different numbers of offspring.
• This leads to evolutionary change that, being random, has nothing to do with adaptation.
• The influence of this process on important evolutionary change, though, is probably minor, because it does not have the molding power of natural selection.
• Natural selection remains the only process that can produce adaptation.

Question 15

“Only” a Theory

Answer 15

• A scientific theory is “a statement of what are held to be the general laws, principles, or causes of something known or observed.” - Oxford English Dictionary
• For a theory to be considered scientific, it must be testable and make verifiable predictions.
  That is, we must be able to make observations about the real world that either support it or disprove it.
• A good theory makes predictions about what we should find if we look more closely at nature. And if those predictions are met, it gives us more confidence that the theory is true.
• Because a theory is accepted as “true” only when its assertions and predictions are tested over and over again, and confirmed repeatedly, there is no one moment when a scientific theory suddenly becomes a scientific fact.
• In the process of becoming truths, or facts, scientific theories are usually tested against alternative theories.
• A scientific theory is different from casually saying a theory in regular language.

(read more on pg 17 - 20)