Acquired characteristics and horizontal gene transfer

Stretching your neck makes your children's necks longer? That is the idea in Lamarck's giraffe example. It isn't just that parents and offspring resemble each other. The claim is that something an animal does during its life changes a characteristic that can then be inherited.

I want evidence for that. Think about the difference between inheriting a parent's hair color and inheriting a scar the parent acquired in an accident. Those are different kinds of claims. The opening tells us biologists rejected the inheritance of acquired characteristics because they could not identify a genetic mechanism that would make it plausible. Then we get the turn: new research has uncovered examples. All right—what are they, and how well do they fit the claim?

The first involves bacterial cell walls. Ordinarily, enzymes build and break down those walls as the bacterium grows. If an experimenter removes the wall completely, however, the bacterium continues growing and multiplying without walls. Its descendants also lack them. The explanation is a change in the interactions among genes, while the genes remain unchanged (paragraph 2). Keep that distinction. We have an inherited change in a characteristic without adding or removing a gene.

I can understand that result while still wondering how closely it resembles an animal stretching an organ. We don't have to settle that concern to follow what the writer is doing: presenting this as an example of an environmentally produced change that can be inherited.

Paragraph 3 introduces a different mechanism. This time, genetic material is added or removed. A virus introduces a gene that makes fruit flies vulnerable to carbon dioxide poisoning, and infected flies pass it to their offspring. Keeping the flies warm while they produce eggs eliminates the virus from the eggs, and the offspring are resistant. That is a different example from changing how existing genes interact.

The E. coli example adds another way to acquire genetic material. A bacterium receives a plasmid—a small ring of genetic material—from another bacterium, incorporates it, and passes it to offspring. Notice the two steps: acquiring material from another organism, then passing it to descendants. Don't collapse every kind of transfer into one process.

Why does that matter? Acquiring an existing capability could be much faster than waiting for it to develop through random mutation and natural selection. The photosynthesis example illustrates that possibility. The claim concerns the time needed to acquire the ability, not the speed at which a cell performs photosynthesis once it has it.

The ending names the distinction. Vertical inheritance comes from ancestors. Horizontal acquisition comes from sources such as viruses, plasmids, or other organisms; the writer says it may even occur between organisms considered unrelated.

I'm still questioning the final jump. Evidence that organisms can acquire genetic material from their surroundings doesn't immediately look like the giraffe stretching its neck. But that is my reaction, not a replacement for the writer's conclusion. The writer thinks horizontal transmission could supply the missing mechanism and might eventually establish Lamarck's hypothesis. The qualification matters: may prove correct is not the same as has proved correct.

My prediction is that recent discoveries may support inheritance of acquired characteristics, including by supplying a possible mechanism. An answer limited to E. coli would miss the broader point; an answer announcing that Lamarck has been vindicated would go further than the conclusion.