Question

Elephant Tusklessness
Sclentists working in Gorongosa National Park are trying to determine the genes responsible for tusk development in elephants. Normally, more than 90% of female African elephants have tusks. But in Gorongosa National Park, which has a history of heavy poaching, about 50% of the elephants are tuskless. To study this striking phenomenon, scientists are searching for the gene or genes responsible for tusk development and how variations in these genes can lead to tusklessness.
During the Mozambican Civil War (1977-1992), elephants were heavily hunted for ivory. After the war, researchers documented a significant increase in tuskless female elephants in Gorongosa National Park. Figure 1 shows the percentage of tuskless females pre- and post-war. This change illustrates how human actions can alter evolutionary pressures.

Using evidence from the tuskless elephant case, explain how natural selection operates on heritable varlation to drive adaptation of populations. In your response, Include:
1. The role of human-induced selective pressure
2. Why tusklessness increased over time
3. How does this exemplify the four factors of evolution?

Write in a 5th graders response and include evidence

Answer 1

Here is a simple explanation a 5th grader can understand.

Short answer
- Poachers (people hunting elephants for ivory) caused a big change. Because poachers killed elephants with tusks, elephants without tusks were more likely to live and have babies. Over time, more baby elephants were born without tusks. Scientists saw that before the war more than 90% of female African elephants had tusks, but after the heavy poaching in Gorongosa many more females were tuskless (about half were tuskless). This is natural selection changing the population.

1) The role of human-induced selective pressure
- Poaching is the human-caused pressure. Poachers wanted ivory, so they mainly killed elephants with tusks.
- That meant elephants with tusks died more often. Elephants without tusks were less likely to be killed and more likely to survive and have babies.

Evidence: Heavy hunting happened during the Mozambican Civil War (1977–1992). After the war scientists found many more tuskless females in Gorongosa than before.

2) Why tusklessness increased over time
- Some elephants already had genes that made them tuskless. Those genes are passed from parents to babies (they are heritable).
- Because tuskless elephants survived poaching more often, they had more babies. Those babies inherited the tuskless genes.
- With each generation, the tuskless genes became more common. That is why the number of tuskless elephants increased.

Evidence: Before the war, over 90% of females had tusks (so tuskless was rare). After heavy poaching, about 50% of the elephants in Gorongosa were tuskless — a big change in a short time.

3) How this shows the four factors of evolution
- Natural selection: Poaching killed tusked elephants more, so tuskless elephants left more babies. This is direct natural selection by humans.
Evidence: Big rise in tuskless females after the poaching period.
- Mutation: New gene changes (mutations) can make new traits. In this case, tuskless genes were already in the population from past mutations.
Evidence: Tuskless elephants existed before the war, so the genetic variation was already present.
- Gene flow: If elephants move in or out of Gorongosa, they can carry tusk or tuskless genes with them. That can change how common a trait is.
Evidence: Movement of elephants between parks can add or remove genes (scientists consider elephant movement when studying populations).
- Genetic drift: When many elephants were killed, the population became small. In small groups, random chance can change which genes are common.
Evidence: Heavy hunting dramatically reduced numbers during the war, creating a population bottleneck where chance played a bigger role.

Conclusion
- The tuskless elephants of Gorongosa are a clear example of evolution by natural selection caused by people. Because tusklessness is heritable and tusked elephants were killed more often, tuskless genes became more common in the population. Scientists use the before-and-after numbers (over 90% tusked before, about 50% tuskless after) as evidence that human actions changed the elephants’ evolution.