How could a species be engineered to go extinct?

Question

Non-biology background here. I read this very interesting article: https://www.wired.com/story/crispr-eradicate-invasive-species/ However I am having a hard time wrapping my head around something: From my basic understanding of natural selection, a gene/trait will spread if it gives the group a relatively higher chance of having children, who will pass on the trait, etc. However in this example, the trait is **infertility**! Doesn't it go completely against natural selection? How could this spread??

Answer 1

So first, not all traits are adaptive (i.e., they don't all confer higher fitness, some are neutral, a lot are negative) - that is one of the common misconceptions about evolution.

Natural selection is only one of many forces of evolution - another being genetic drift, which is variation in (what we'll call) traits due to stochastic effects.

For example, on islands stochastic effects tend to be much more pronounced because large populations cannot be maintained. In addition, phenomena, such as bottle-necking and founder effects can occur, which is when (1) a proportion of the population is killed, reducing genetic diversity, and (2) a small proportion of an original population moves to another area and starts a new, sub-population; respectively.

These two effects can be responsible for the propagation of deleterious traits, if say the original founders of a island's population had the negative trait (in your example, were carriers for a trait that ultimately caused infertility).

Real-world examples of this include the island of Pingelap in the Pacific, which had its population reduced to 20 - and after repopulating, now has the highest incidence of complete colorblindness (clearly, a non-adaptive trait); as well as the Amish, which due to a founder effect, have a high rate of polydactyly (i.e., having too many fingers (which, again is non-adaptive.)

There are plenty of other mechanisms by which deleterious traits can persist, that occur despite natural selection, but I don't want to talk about too much in one post.

Something to read about for your particular example would be (1) methods of reproductive isolation, (2) biological control, and perhaps (3) the common misconceptions of evolution.

Good luck.