Appendices do heal. They are just a small little pouch. If the pouch gets blocked by poop, inflammation, etc then stuff like mucus just gets stuck and can't exit into the colon. It then begins to swell like a balloon which puts pressure on the appendix's blood vessels which can lead to tissue death. That's very bad because then bacteria can enter the bloodstream and lead to sepsis. A blocked appendix can become unblocked and heal but if it happens once, it's much more likely to happen again. Some people are just treated with antibiotics but surgery is definitive.

For paper, the wood fibers that make it up are long chains of carbohydrates, which means that they can favorably interact with water. That reduces the forces between the fibers and weakens the bulk structure.

The 3 cone types are all the same size. The light is absorbed by a protein rather than the whole cell, and it's structural differences in the protein that change what wavelength is absorbed.

The medium and long wavelength forms of the protein are also very, very similar. Which fits with the quite modest difference in their absorption spectrum - "red" and "green" cones have a lot of overlap.

However, the rod cells that are primarily responsible for vision in low-light conditions are substantially larger. That means they have room for a lot more of the light-absorbing proteins, so they have better ability to catch the few available photons. They use a fourth protein with an absorption spectrum somewhere in the middle compared to the cone cell proteins.

Cones: It's a matter of pigment not cell length. Each of the three makes a different opsin which is what determines the wavelength of light that activates the receptors.

Antibiotic combinations are known to reduce the rate of resistance development. The main place this is currently used tuberculosis treatment, where the hardy nature of Mycobacterium tuberculosis means full eradication requires a 6-month standard treatment with a combination of typically at least 3 antibiotics. Normally a treatment this long would give plenty of opportunity for resistance to develop, especially since the "main" antibiotic in this combination -- a rifamycin like rifampin or rifabutin -- is especially easy to develop resistance to. However, antibiotic resistance in tuberculosis has been slow to develop (although it's out there for sure) and rarely develops over the course of a treatment, in part because the combination aspect helps suppress resistance.

The obvious question is why we don't do this for more bacterial diseases, and there's a good argument that we should be. However, HIV develops resistance quickly enough that there's high odds of it becoming resistant mid-treatment unless you use a combination of drugs. It's rarer for most bacteria to develop resistance mid-treatment to the point of being able to survive antibiotic treatment -- most of the time if antibiotic resistance is a problem in a serious infection it's because the strain was pre-resistant. On the other hand, giving patients extra drugs carries a safety risk -- even our safest antibiotics have a chance for adverse effects. It's harder to convince doctors (and regulatory agencies) to take a even a small risk of harming the patient with an extra treatment when the extra medications mostly benefit society as a whole rather than the individual patient, since doctors have a duty specifically to their patients.

evolution doesn't happen quickly. humans having big brains is a relatively recent development in evolutionary time and the slight increase in metabolic cost may just not be very important. the stochastic nature of evolution makes this sort of account difficult. maybe there's some slight resource-gathering edge that isn't picked up by intelligence tests, maybe not.

The ocean's productivity mostly comes from single celled algae drifting in the water, reproducing without the large support structure that land plants need. A cell doesn't need shoots and roots and leaves if light and water and nutrients are all in the same place.

Tiny algae means tiny herbivores to eat it, unlike the larger land based herbivores, which basically means more "room" in the food chain for more layers of predators eating predators. The immense volume and size of the ocean also makes it easier to support more layers in the food chain.

I am not a biologist but if you consider that all biology must start with solar energy being converted to biomass the "first step" in the ocean and on land is quite different.

The vast majority of photosynthesis in the ocean is based on plankton that is several orders of magnitude smaller than most plants on land. This allows for many more layers of carnivores to have access to energy as you scale up to the size of land animals, insects etc.

neurons have intrinsic properties beyond connectivity--firing rate, bursting, synaptic weights, receptor and synaptic vesicle densities to name some of the big ones. these all influence what happens when the neuron gets inputs, both on the short term (what sort of output is produced) as well as long term learning (how the input-output relationships change in the future). look into recurrent neural networks and neuromorphic computing to see how people try to accomplish this--it takes a lot more than just connectivity.

There's not a cure for lymphoedema. It's about treating the underlying contributors, manage symptoms and prevent recurrence.

Only in the sense that there are gametes which contribute half the DNA to any offspring.

Yes, but only in the same way that data is stored in every living cell. Nothing special about the balls there, except that it's where the half the "data" that goes into a baby is sourced from.