托福口语 Task 3

In biology, organisms often develop traits that appear to reduce their own fitness in order to increase the survival chances of their close relatives. This phenomenon is called kin selection. According to the theory, an individual may sacrifice its own reproduction or safety if doing so helps its genetic relatives—such as siblings or offspring—pass on shared genes. The key is that the helper and the recipient share a significant proportion of genes, so the overall genetic success of the family unit can be enhanced even if the individual's own direct reproduction suffers.

Professor: Let’s look at a real example. In some bird species, like the Florida scrub jay, young birds often stay at their parents' nest instead of building their own nests. They help feed the new chicks, defend the territory, and warn against predators. Now, these helpers don't have their own offspring that year—so they lose direct reproduction. But why do they do it? Because they share about 50% of their genes with their siblings. By helping their parents raise more chicks, they ensure that many copies of their own genes are passed on indirectly. In fact, studies show that nests with helpers fledge more chicks than nests without helpers. So even though the helper doesn't reproduce, its genes are still well represented in the next generation.