The Classification of Living Things and the Discovery of Evolution

1. Chapter 2 Biology and Evolution

2. Chapter Outline • Evolution and Creation Stories • The Classification of Living Things • The Discovery of Evolution • Heredity • Evolution, Individuals, and Populations • Adaptation and Physical Variation

3. Great Chain of Being • An early form of classification of living things used in Europe. • Developed by Aristotle in ancient Greece over 2,000 years ago. • Categories were based upon visible similarities with a member of each category considered a “primate”. • The primate of rocks was the diamond. • Humans were at the very top of the ladder, just below the angels.

4. Systema Naturae • Classificatory system developed by Carolus Linnaeus in the 18th century to classify all living things. • Linnaeus classified living things into categories that are progressively more inclusive on the basis of internal and external visual similarities. • Speciesare the smallest working units in biological classificatory systems. • Species are subdivisions of larger, more inclusive groups, called genera.

5. Criteria of Linnaeus Classificatory System • Body structure: A Guernsey cow and a Holstein cow are the same species because they have identical body structure. • Body function: Cows and horses give birth to live young. Although they are different species, they are closer than either cows or horses are to chickens. • Sequence of bodily growth: At the time of birth—or hatching out of the egg—young cows and chickens resemble their parents in their body plan.

6. Taxonomy • The science of classification. • It is based on more than body structure, function, and growth; today scientists base taxonomy also on molecular comparisons.

7. Analogies • In biology, structures possessed by different organisms that are superficially similar due to similar function; without sharing a common developmental pathway or structure.

8. Homologies • In biology, structures possessed by two different organisms that arise in similar fashion and pass through similar stages during embryonic development though they may possess different functions.

9. Classification of Humans INSERT ½ TABLE 2.1 P. 31

10. Classification of Humans INSERT ½ TABLE 2.1 P. 31

11. Theory of Natural Selection • Charles Darwin formulated the theory of natural selection and published it in 1859. • Darwin combined his observations into the theory ofnatural selection as follows: • All species display variation and have the ability to expand beyond their means of subsistence. • In their “struggle for existence,” organisms with variations that help them survive will reproduce more successfully. • Nature selects the most advantageous variations, and species evolve.

12. The Transmission of Genes • A gene is a portion of the DNA molecule that contains a sequence of base pairs that encode a particular protein. • Mendel deduced the presence and activity of genes by experimenting with garden peas to determine how traits are passed from one generation to the next. • He discovered that inheritance was particulate, rather than blending, as Darwin thought.

13. The Law of Segregation • Units controlling the expression of visible traits come in pairs, one from each parent, and retain their separate identities over the generations rather than blending into a combination of parental traits in offspring.

14. The Law of Independent Assortment • The Mendelian principle that genes controlling different traits are inherited independently of one another.

15. Chromosones • In the cell nucleus, chromosones are the structures visible during cellular division containing long strands of DNA combined with a protein. • When chromosomes were discovered at the start of the 20th century, they provided a visible vehicle for transmission of traits proposed in Mendel’s laws.

16. DNA • Deoxyribonucleic acid. • The genetic material consisting of a complex molecule whose base structure directs the synthesis of proteins. • In 1953 James Watson and Francis Crick found that genes are actually portions of molecules of DNA.

17. DNA Structure INSERT FIGURE 2.1 P. 34

18. Alleles • Alternate forms of a single gene. • Example: • The gene for a human blood type in the A-B-O system refers to a specific portion of a DNA molecule, and alleles correspond to alternate forms of this gene that determine the specific blood type (A allele, B allele, C allele).

19. Humane Genome • The complete sequence of human DNA. • The genome contains 3 billion chemical bases, with about 20,000–25,000 functioning genes, a number similar to that found in most mammals. • Of the 3 billion bases, humans and mice are about 90 percent identical.

20. Cell Division • In order to grow and maintain good health, the body cells of an organism must divide and produce new cells. • Cell division is initiated when chromosomes replicate, forming a second pair that duplicates the original pair of chromosomes in the nucleus.

21. Mitosis • A kind of cell division that produces new cells having exactly the same number of chromosome pairs as the parent cell. • The DNA “unzips” between the base pairs—adenine from thymine and guanine from cytosine. • Each base on each now-single strand attracts its complementary base, reconstituting the second half of the double helix. • Each new pair is surrounded by a membrane and becomes the nucleus of a new cell. • As long as no errors are made in the process, cells within organisms can divide to form daughter cells that are exact genetic copies of the parent cell.

22. Meiosis (Sexual Reproduction) • A kind of cell division that produces sex cells, each of which has half the number of chromosomes found in other cells of the organism. • In humans this involves 23 pair of chromosomes. • Sexual reproduction increases genetic diversity and has contributed to adaptations among sexually reproducing species.

23. Meiosis • Meiosis is cell division that produces sex cells, each of which has half the number of chromosomes found in other cells. • If two regular body cells, each containing 23 pairs of chromosomes, merged, the result would be an individual with 46 pairs of chromosomes; they could not survive. • This doesn’t occur because sex cells that join to form a new individual are the product of meiosis.

24. Mitosis and Meiosis INSERT FIGURE 2.2 P. 37

25. The Punnett Square INSERT FIGURE 2.3 P. 37

26. Genotype • The alleles possessed for a particular trait.

27. Heterozygous • Refers to a chromosome pair that bears different alleles for a single gene.

28. Homozygous • Refers to a chromosome pair that bears identical alleles for a single gene.

29. Dominance • The ability of one allele for a trait to mask the presence of another allele.

30. Recessive • An allele for a trait whose expression is masked by the presence of a dominant allele.

31. Dominance and Recessiveness • Recessive alleles can be handed down for generations before they are matched with another recessive allele in the process of sexual reproduction and show up in the phenotype. • The presence of the dominant allele masks the expression of the recessive allele.

32. Phenotype • The observable or testable appearance of an organism that may or may not reflect a particular genotype due to the variable expression of dominant and recessive alleles.

33. Hemoglobin • The protein that carries oxygen in the red blood cells.

34. Polygenetic Inheritance • When two or more genes contribute to the phenotypic expression of a single character.

35. Evolution, Individuals and Populations • In biology, a population is a group of similar individuals that can and do interbreed. • The gene pool refers to the genetic variants possessed by all members of a population. • Natural selection also takes place within populations. • Over generations, the relative proportions of alleles in a population changes according to the reproductive success of individuals within that population. This is called microevolution.

36. Microevolution • At the level of population genetics, evolutionis defined as changes in allele frequencies in populations, or microevolution. • Four evolutionary forces—mutation, gene flow, genetic drift, and natural selection—are responsible for the genetic changes that underlie biological variation. • These evolutionary forces create and pattern diversity.

37. Mutation • Mutation is the ultimate source of evolutionary change that constantly introduces new variation. • For sexually reproducing species like humans, only mutations that occur in sex cells are of any evolutionary consequence. • Mutations may arise whenever copying mistakes are made during cell division.

38. Some Causes of Mutation • Environmental factors such as dyes, antibiotics, and chemicals may increase the rate at which mutations occur. • Radiation (industrial or solar) is also a cause of mutations. • Stress can increase mutation rates, increasing the diversity necessary for selection if successful adaptation is to occur.

39. Mutation Process • In all multicellular animals, genetic material ensures that mutations will occur. • Genes are split by stretches of DNA that are not a part of that gene, increasing the chances that a simple mistake in the process of copying DNA will cause mutations. • Mutations occur randomly and do not arise out of need for some new adaptation.

40. Genetic Drift • Refers to chance fluctuations of allele frequencies of the gene pool of a population. • These changes are a result of random events at the individual level. • Genetic drift is likely to have been an important factor in human evolution, because until 10,000 years ago, all humans were food foragers who lived in small, self-contained populations.

41. Founder Effects • A particular kind of genetic drift that may occur when an existing population splits up into two or more new ones, especially if one of the new populations is founded by a particularly small number of individuals. • It is unlikely that the gene frequencies of the smaller population will be representative of those of the larger one.

42. Gene Flow • The introduction of new alleles from nearby populations. • Interbreeding allows genes to flow in and out of populations, increasing variation within a population. • Migration and geographical factors lead to gene flow. • Among humans, social factors such as mating rules, intergroup conflict, and our ability to travel great distances affect gene flow.

43. Natural Selection • The evolutionary process through which genetic variation at the population level is shaped to fit local environmental conditions. • Over time, changes in the genetic structure of the population are visible in the biology or behavior of a population, and such genetic changes can result in the formation of new species.

44. Sickle-Cell Trait • The sickle-cell trait, caused by the inheritance of an abnormal form of hemoglobin, is an adaptationfound in regions in which malaria is common. • In these regions, the sickle-cell trait plays a beneficial role. • In other parts of the world, the sickling trait is not advantageous and sickle- cell anemia is harmful.

45. Sickle-Cell Anemia • A disease in which the oxygen-carrying red blood cells change shape and clog the circulatory system. • Geneticists predict that as malaria is brought under control, within several generations, there will be a decline in the number of individuals who carry the allele responsible for sickle-cell anemia.

46. Sickle-cell Anemia INSERT TOP PHOTO P. 43

47. Adaptation and Physical Variation • Anthropologists study biological diversity in terms ofclines, or the continuous gradation over space in the form or frequency of a trait. • Clinal analysis of a continuous trait, such as body shape, allows anthropologists to interpret human variation in body build as an adaptation to climate. • People native to cold climates tend to have greater body bulk relative to their arms and legs than people native to hot climates.