Prep Guide: Human Evolution

Key Concepts (Recall & Understanding)

Evolution: The process of change in the heritable characteristics of biological populations over successive generations.
Lamarck's Theory: Based on the principles of "use and disuse" and the "inheritance of acquired characteristics." This theory is now largely discredited.
Darwin's Theory of Natural Selection: Based on observations of variation, inheritance, and the struggle for existence. The core idea is "survival of the fittest," where individuals with advantageous traits are more likely to survive and reproduce.
Industrial Melanism: A classic example of natural selection, where the frequency of dark-colored peppered moths increased in polluted industrial areas because they were better camouflaged against soot-covered trees.
Key Human Ancestors (Hominins):
- Australopithecus: Early bipedal hominin with a small brain and ape-like features.
- Homo habilis ("Handy Man"): Known for being the first to use stone tools; had a larger brain than Australopithecus.
- Homo erectus ("Upright Man"): Taller, with a larger brain, more sophisticated tools, and was the first to control fire and migrate out of Africa.
- Neanderthals: Stocky build, large brain, adapted to cold climates, had complex tools and culture.
- Cro-Magnon: An early form of Homo sapiens, known for their art (cave paintings), advanced tools, and tall stature.
- Homo sapiens sapiens (Modern Man): Characterized by a high forehead, prominent chin, and large brain.

Application Corner

According to Lamarck's theory, how would the strong, muscular arms of a blacksmith develop, and what would happen to this trait in his children?
- Answer: According to Lamarck, the blacksmith's arms would become strong through constant use (use and disuse). He would then pass this acquired characteristic directly to his children, who would be born with stronger arms.
The appendix in humans is a vestigial organ. How does Darwin's theory of natural selection explain the presence of such an organ?
- Answer: Darwin's theory would suggest that the appendix is a remnant of a larger, functional organ (likely a cecum for digesting cellulose) in our distant ancestors. As our diet changed, this organ was no longer needed. Individuals with a smaller, less functional version were not disadvantaged, and since maintaining a large, useless organ requires energy, natural selection may have favored its reduction over many generations.

Analytical Thinking

Odd One Out: Australopithecus, Homo erectus, Cro-Magnon, Gorilla.
- Odd One: Gorilla.
- Category: The rest are all hominins (human ancestors) in the direct line of human evolution.
Arrange in Chronological Order: Place the following hominins in the correct order of their appearance on Earth: Neanderthals, Homo habilis, Australopithecus, Homo sapiens sapiens.
- Answer: 1. Australopithecus, 2. Homo habilis, 3. Neanderthals, 4. Homo sapiens sapiens.

One of the earliest and most significant changes in human evolution was the move to bipedalism (walking on two legs). Hominins like Australopithecus were among the first to walk upright. This transition from quadrupedal (four-legged) locomotion had profound consequences. It freed the hands for carrying food, tools, and infants. It also allowed for a more efficient way to travel long distances and may have helped with thermoregulation by exposing less of the body to the direct sun. However, it also came with disadvantages, such as making individuals slower runners and causing lower back problems. The shift to bipedalism is a key case study in evolutionary trade-offs and is considered a foundational step that paved the way for all subsequent human evolution, including the development of larger brains and tool use.

Assertion-Reason Practice

Assertion (A): The story of the peppered moth is an example of natural selection in action. Reason (R): The change in the environment (soot-covered trees) led to a change in which moth color variant had a higher survival rate.

(a) Both (A) and (R) are true and (R) is the correct explanation of (A). (b) Both (A) and (R) are true but (R) is not the correct explanation of (A). (c) (A) is true but (R) is false. (d) (A) is false but (R) is true.

Answer: (a) Both (A) and (R) are true and (R) is the correct explanation of (A). The environmental change directly influenced the selective pressure (predation by birds), causing the population to evolve towards the better-camouflaged variant. This is the essence of natural selection.

HOTS (Higher-Order Thinking Skills) Question

While a larger brain is a hallmark of human evolution, it comes at a significant cost: a large brain requires a huge amount of energy to run, and a large head makes childbirth more difficult and dangerous. From an evolutionary perspective, what benefits of a larger brain must have outweighed these considerable costs?

Answer: The benefits of a larger brain must have been immense to outweigh the costs. These likely included:
1. Advanced Tool Use: The ability to design, create, and use more complex tools for hunting, defense, and processing food.
2. Complex Social Structures: The capacity for language, cooperation, and the formation of complex social groups, which would have improved collective hunting, defense, and the sharing of knowledge.
3. Problem-Solving and Adaptability: The ability to think abstractly, plan for the future, and adapt to new and changing environments, which allowed humans to spread across the globe.
4. Cultural Transmission: The ability to learn and pass on knowledge, skills, and culture to the next generation, allowing for cumulative learning that is much faster than genetic evolution. These cognitive advantages would have significantly increased the chances of survival and reproduction, thus favoring the evolution of a larger brain despite its high energy and childbirth costs.

Specimen Prep - Evolution