1. The Theory of Evolution
Lesson 2
The Theory of Evolution
By Natural Selection

2. Charles Darwin
Scientists had evidence that showed changes in species over time, but they didn’t know how.
Charles Darwin was one scientist who struggled with this idea.

3. Charles Darwin
Darwin was a NATURALIST, a person who studies plants and animals by observing them.
He was not the first scientists to develop a theory about evolution, but his theory is the one best supported by evidence.

4. Charles Darwin
Darwin’s breakthrough came while on a voyage to the Galapagos Islands (near the equator off the pacific coast of South America).
Darwin noticed slight differences in animals living on each of the islands; he later decided that some varieties were different enough to be classified as different species.

5. Darwin’s Theory
Darwin noticed a relationship between each species and the food sources of the island it lived on.

6. Darwin’s Theory
The species of tortoise that lived on an island with tall cacti had long necks, while the species of tortoise on an island with lots of short grass had short necks.

7. Darwin’s Theory

8. Darwin’s Theory
Darwin thought all the Galapagos tortoises shared a common ancestor that came to one of the islands millions of years ago.
He knew that members of the same species each have slight differences called VARIATIONS.
Darwin didn’t know about heredity, but he realized that variations in populations could help explain how the different species of Galapagos tortoises and finches evolved.

9. Darwin’s Theory
Darwin knew that food is a LIMITING RESOURCE, so members of a species that live in the same area compete for food.
If a variation benefited a tortoise, allowing it to compete better for food than other tortoises (more “fit” to its environment), the tortoise was more likely to live longer, reproduce more, and pass on its variations (traits) to its offspring.

10. Natural Selection
NATURAL SELECTION: Individuals within a population that possess variations which help them survive in their environment tend to live longer, compete better, and reproduce more than individuals that do not have the beneficial trait.

11. Adaptations
An ADAPTATION is an inherited trait that increases an organism’s chance of surviving and reproducing in its environment.
Scientists classify adaptations into three categories.

12. Adaptation

13. Adaptations
STRUCTURAL ADAPTATIONS involve color, shape, and other physical characteristics.
Camoflauge

14. Adaptations
BEHAVIORAL ADAPTATIONS involve the way organisms behave or act.

15. Adaptations
FUNCTIONAL ADAPTATIONS involve internal body systems that affect biochemistry.

16. Environmental Interactions
A structural adaptation that aids members of a species in blending in with their environment is called CAMOUFLAGE.

17. Environmental Interactions
An adaptation in which one species resembles another species is called MIMICRY.

18. Environmental Interactions
The living and nonliving parts of the environment are always changing; species that cannot adapt to such changes will become extinct.

19. Natural Selection vs. Artificial Selection
Darwin’s theory of natural selection predicts that species will develop adaptations, which explains why we see such a diversity of organisms that are perfectly suited to thrive in their environment.

20. Natural Selection vs. Artificial Selection
SELECTIVE BREEDING is the practice of breeding organisms for desired characteristics.

21. Natural Selection vs. Artificial Selection
Darwin realized that natural selection and artificial selection are similar processes.
In natural selection, nature causes the changes in the species.
In artificial selection, humans cause the changes in the species.

22. Common Misconceptions about Evolution
It is true that natural selection weeds out individuals that are unfit in a particular situation, but for evolution, “good enough” is good enough. No organism has to be perfect. For example, many taxa (like some mosses, protists, fungi, sharks, opossums, and crayfish) have changed little over great expanses of time. They are not marching up a ladder of progress. Rather, they are fit enough to survive and reproduce, and that is all that is necessary to ensure their existence.
Other taxa may have changed and diversified a great deal—but that doesn’t mean they got “better.” After all, climates change, rivers shift course, new competitors invade—and what was “better” a million years ago, may not be “better” today.

23. Common Misconceptions about Evolution
Use and disuse – Individuals lose characteristics they do not require (or use) and develop characteristics that are useful.
Inheritance of acquired traits – Individuals inherit the traits of their ancestors.
Natural selection leads to adaptation, but the process doesn’t involve “trying.” Natural selection involves genetic variation and selection among variants present in a population. Either an individual has genes that are good enough to survive and reproduce, or it does not—but it can’t get the right genes by “trying.”
Jean-Baptiste Lamarck

24. Common Misconceptions about Evolution
Natural selection has no intentions or senses; it cannot sense what a species “needs.” If a population happens to have the genetic variation that allows some individuals to survive a particular challenge better than others, then those individuals will have more offspring in the next generation, and the population will evolve. If that genetic variation is not in the population, the population may still survive (but not evolve much) or it may die out. But it will not be granted what it “needs” by natural selection

25. Common Misconceptions about Evolution
Evolutionary theory deals mainly with how life changed after its origin. Science does try to investigate how life started (e.g., whether or not it happened near a deep-sea vent, which organic molecules came first, etc.), but these considerations are not the central focus of evolutionary theory. Regardless of how life started, afterwards it branched and diversified, and most studies of evolution are focused on those processes.

26. Symbiotic Relationships
Symbiosis- two species living together
4 Types of symbiosis:
1. Commensalism
2. Parasitism
3. Mutualism
4. Predation
Cleaning shrimp

27. Symbiotic Relationships
Commensalism-
one species benefits and the other is neither harmed nor helped
Ex. orchids on a tree

28. Symbiotic Relationships
Parasitism-
one species benefits (parasite) and the other is harmed (host)
Parasite-Host relationship

29. Symbiotic Relationships
Mutualism-
beneficial to both species
Ex. cleaning birds and cleaner shrimp
The Egyptian plover takes insects from the backs of buffaloes, giraffes and rhinos. The plover has also been observed taking leeches from the open mouths of crocodiles! In this association the plover receives a supply of food and the other animal rids itself of unwelcome pests

30. Predation
One benefits, one DIES!

31. = 1 species Type of relationship Species harmed Species benefits
Species neutral
Commensalism
Parasitism
Mutualism
= 1 species