Table of contents

1. Introduction to Biology2h 42m
2. Chemistry3h 37m
3. Water1h 26m
4. Biomolecules2h 23m
5. Cell Components2h 26m
6. The Membrane2h 31m
7. Energy and Metabolism2h 0m
8. Respiration2h 40m
9. Photosynthesis2h 49m
10. Cell Signaling59m
11. Cell Division2h 47m
12. Meiosis2h 0m
13. Mendelian Genetics4h 44m
14. DNA Synthesis2h 27m
15. Gene Expression3h 6m
16. Regulation of Expression3h 31m
17. Viruses37m
- Viruses
  37m
18. Biotechnology2h 58m
19. Genomics17m
- Genomes
  17m
20. Development1h 5m
21. Evolution3h 1m
22. Evolution of Populations3h 53m
23. Speciation1h 37m
24. History of Life on Earth2h 6m
25. Phylogeny2h 31m
26. Prokaryotes4h 59m
27. Protists1h 12m
28. Plants1h 22m
29. Fungi36m
- Fungi
  19m
- Fungi Reproduction
  17m
30. Overview of Animals34m
- Overview of Animals
  34m
31. Invertebrates1h 2m
32. Vertebrates50m
33. Plant Anatomy1h 3m
34. Vascular Plant Transport1h 2m
- Water Potential
  1h 2m
35. Soil37m
- Soil and Nutrients
  20m
- Nitrogen Fixation
  16m
36. Plant Reproduction47m
- Flowers
  33m
- Seeds
  14m
37. Plant Sensation and Response1h 9m
38. Animal Form and Function1h 19m
39. Digestive System1h 10m
- Digestion
  1h 3m
- Blood Sugar Homeostasis
  7m
40. Circulatory System1h 49m
41. Immune System1h 12m
42. Osmoregulation and Excretion50m
- Osmoregulation and Excretion
  50m
43. Endocrine System1h 4m
- Endocrine System
  1h 4m
44. Animal Reproduction1h 2m
- Animal Reproduction
  1h 2m
45. Nervous System1h 55m
- Neurons and Action Potentials
  1h 8m
- Central and Peripheral Nervous System
  46m
46. Sensory Systems46m
- Sensory System
  46m
47. Muscle Systems23m
- Musculoskeletal System
  23m
48. Ecology3h 11m
49. Animal Behavior28m
- Animal Behavior
  28m
50. Population Ecology3h 41m
51. Community Ecology2h 46m
52. Ecosystems2h 36m
53. Conservation Biology24m
- Conservation Biology
  24m

21. Evolution

Introduction to Evolution and Natural Selection

General Biology

21. Evolution

Introduction to Evolution and Natural Selection

Previous problemNext problem

Struggling with General Biology?

Join thousands of students who trust us to help them ace their exams!Watch the first video

Multiple Choice

Why does malaria persist in the human population despite its harmful effects?

Because malaria parasites cannot be transmitted between humans

Because humans have developed complete immunity to malaria

Because the sickle cell allele provides a selective advantage against malaria in certain populations

Because malaria only affects non-human animals

Previous problemNext problem

Verified step by step guidance

Understand the context of malaria: Malaria is caused by Plasmodium parasites, which are transmitted to humans through the bite of infected female Anopheles mosquitoes. It is a disease that can cause severe health issues and even death.

Recognize the genetic connection: In certain human populations, particularly those in regions where malaria is prevalent, the sickle cell allele (a variant of the hemoglobin gene) provides a selective advantage. Individuals who are heterozygous for the sickle cell allele (carrying one normal allele and one sickle cell allele) are less likely to suffer severe effects of malaria.

Explain the mechanism of advantage: The sickle cell allele alters the shape of red blood cells, making it harder for the malaria parasite to infect and reproduce within these cells. This reduces the severity of malaria in individuals with the heterozygous genotype.

Discuss the persistence of malaria: Despite its harmful effects, malaria persists because the sickle cell allele does not eliminate the disease entirely. Instead, it creates a balance where the allele is maintained in the population due to its protective effect against malaria, even though individuals homozygous for the sickle cell allele suffer from sickle cell disease.

Conclude with evolutionary implications: This phenomenon is an example of balanced polymorphism, where the presence of a harmful allele (sickle cell allele) is maintained in the population because it provides a survival advantage in the context of another harmful condition (malaria).