Why Whales, the largest animals on Earth, got so big

Significant land life, about 350 million years.

Over 4.5 billion years, less than 15% of the total duration of the planet.

For most of Earth's existance, if you'd come searching for signs of life, you'd have found little but slime and bacterial stew in oceans and ponds. If that.

Pre-agriculture humans were about the same size (apparently, we can tell by measurements of the pelvic bone of ancient skeletons). We shrunk after we switched to agriculture, which basically started out as a steady supply of nutritionally inferior food (which could be indirect evidence that we mainly switched because we ran out of easy-to-forage healthier food). So a typical example of a 'good enough' solution, really.

I am a 6' Netherlander (among the shortest men in my family). I just traveled to Shanghai and met a lot of very short Chinese people - but I was surprised to see that there seemed to be a small population of some young men who were as tall or taller than me.

When I asked about these tall Chinese of a native, she explained that they were from northern China, and that they have a harsher climate and eat more fish and protein than locals. Many of the locals grew up subsistence farming under Mao, mostly eating rice, and she explained that the weak nutrition of the resulting diet resulted in less growth.

This is, of course, anecdotal. But in comparison to Dutch height gain, I haven't heard of a similar change in Dutch nutrition or health, at least not relative to peer countries.

There could very well have been something bigger but never left fossils. I mean fossil creation itself is sort of a miracle. Combined with such an animal really bound to living in the ocean, it would be very difficult for a whale the size of a blue whale to

1: meet the conditions to be fossillized 2: survive millions of years 3: discovered at the bottom of the ocean

According to climate models, much arable farmland will be destroyed by climate change. There will be increasing pressure for protein and calories from all sources. Perhaps whales could be domesticated. If not, rapid changes in ocean energy absorption and chemistry threaten the entire food chain.

Another long-term consideration is industrial protein manufacturing to skip the risks and mess of CAFOs in Brazil and Texas, and fish feeding operations like the horrible fish farms throughout the world from Thailand to Norway. It maybe possible to greatly reduce the risk of a global pandemic if animals and people aren't kept in excesssively close proximity.

Megafauna doesn't have much hope in the Holocene extinction event. One only need to look at the odd survival of avocados which were likely to have died out as humans likely killed their primary seed distribution omni or herbivores. There is little causal data, but it's a contributing factor.

Holocene extinction will likely continue until the entire planet collapses, humans die out or kill everything that isn't or cannot be domesticated. There is simply too much energy already absorbed forcing climate change to be reversed even by redirecting all GDP into geoengineering... Greenland and Antarctica will melt over a thousand years, sea levels will rise 100 m (~300 ft).

Animals don't seek to become anything, evolutionarily. But characteristics and traits offer fitness advantages over alternatives.

It's also difficult to disambiguate primary vs. secondary effects and consequences.

"Skin" is how an animal loses power (by far the biggest power draw inside mammals is keeping the body warm. Obviously in water this is an even bigger problem). "Filling" is how an animal generates power.

That means that smaller animals cannot hope to match the whales in efficiency: for sustaining the same biomass, they need to keep a bigger "skin" warm (add all the skin of all individuals together).

Now when does this matter ? Obviously this would matter a lot in terms of scarcity, at which point it would be much easier for whales to survive than smaller fish. When there is richness of food, smaller is better, as you can move faster and "eat" the available energy faster. However if smaller animals do this to the point that food becomes scarce, they've just screwed themselves.

So you see what happens : the longer the biosphere goes without a major disaster, the bigger animals get (and plants, for that matter). The advantage of being the first mover, where you can be small and still win, disappears, and the advantage of efficiency grows and grows. So when food became scarce, whales, the biggest animals that had the easiest time surviving at that point, became even bigger. That made the difference between different whale species.

This framework allows answering your question: no, if whales went extinct fish would increase in numbers (slightly, in the sense that it'd be less than the biomass of the whales that disappeared). There isn't enough predation to replace the whales at the moment, but that would be very quickly rectified if something happened to them.

The real reason krill is increasing is the slight increase of co2 caused by humans (krill eat plankton, as do most whales). It's tiny when measured compared to total volume, but if you look at it in relative terms co2 has increased quite a bit (amount now vs amount 100 years ago). In reality the plant growth in the world is hampered significantly by the amount of available co2, and the fact that plants use it to store energy, a part of which gets buried and is lost to the depths (literally in the case of krill).

I guess larger organisms are more likely to survive in this scenario. Maybe similar to the reasons why larger vehicles are more efficient for transportation: http://www.sustainablefreight.com.au/case-studies/bigger-is-...