Our Early Ancestors Stalked Eight-Foot-Tall Sloths
newyorker.com
newyorker.com
The smaller the animal, the larger skin_surface:body_mass ratio, thus higher heat loss. The smaller the animal, the shorter the intervals between feedings it can tolerate. A large-bodied animal can go for longer period of time without food, especially if equipped with slow metabolism. In contrast, smaller body and faster metabolism requires frequent feeding, but also allows an animal to out-compete slower, larger ones both in food search, and by out-breeding them.
For any given body plan, an animal can only cover distance roughly relative to its body size; the smaller animal, the harder time it will have to find sufficient food on sparse, hardy cold-climate vegetation. On the other hand, once denser, warm climate vegetation takes hold, it allows smaller herbivores to live in higher density, and with higher breeding rate.
If I remember my biology right, the more an animal has specializations for particular environment or niche, the slower it will adapt to changed circumstances, both in body build, and in behavior & seasonal migration patterns.
Last but not least, a predator population requires certain density of prey to be sustainable. Once plant food becomes abundant due to warming up, and herbivore population grows, the population of predators can be established, and cull the large bodied animals unadapted to heavy predation.
EDIT: As always, Wikipedia comes through [1]. There were species of different sizes, with tree sloths always being smaller than ground sloths [2], the giant of the article
[1] https://en.wikipedia.org/wiki/Sloth#Evolution [2] https://en.wikipedia.org/wiki/Ground_sloth
https://www.theatlantic.com/science/archive/2018/04/in-a-few...
> bunch of bastards to most life on Earth
seem almost synonymous, unfortunately.
This is what I disagree with. Evolution is not a process that is maximizing anything. What survives just survives. We got stuck in a feedback loop that optimized brain size for evolutionary fitness, but we're stuck in a tiny fractal corner of a corner of a corner of the entire space of biological life. E.g. Tardigrades (https://en.wikipedia.org/wiki/Tardigrade) are extremely successful at survival in a huge variety of conditions, and very stable over millions of years without a lot of genetic drift. Similar for cockroaches. We don't consider these "pinnacles" of evolution just because of our arbitrary value system. Yet cockroaches (and all insects, really) serve extremely important jobs in ecosystems which would collapse without them.
Humanism is blind and immoral, IMO.
That's a judgement that a human can make only because our species reached the pinnacle of evolution.
You seem to be implying that evolution is a process with some ideal, perfect outcome that can be achieved, or you're just being sarcastic. I can't tell but both are silly.
Whales are the largest animals alive today, so perhaps they're the pinnacle of evolution.
Implying there's a "pinnacle" of evolution implies evolution has a goal or intended outcome, which it does not.
Humans are the most advanced species? By which metric? Intelligence? Perhaps. Strength? No. Sheer numbers? No. Impact on the environment? Arguably (plants, though not a single species, would probably win that). You might as well say we're the most advanced species because we're the only one that cares enough to give ourselves a trophy for it.
Evolution is not a game to be won nor a process with an end or a goal. We weren't here before, we're here now, and we likely won't be here forever. We're ephemeral.
On the other hand, we're also pretty much the only chance for terrestic life to survive the end of our solar system.
When we take a wider look at life, this just isn't universal. If you look at ecosystems in very stable environments (e.g. caves), the ecosystem as a whole tends to come into balance over time, where species are not aggressively try to outcompete their competitors, but instead fit into comfortable little niches so that the system as a whole keeps functioning well. In fact, evolution works on the ecosystem scale as well, and systems with aggressive species tend to be very unstable and prone to crashes. In environments with constant change, then ecosystems are constantly changing and competition becomes more fierce, benefiting aggressive species. This is not always the case, so I don't think it's useful to assume that everything is trying to move as aggressively as possible; otherwise evolution would select against species with long gestation periods and tend towards shorter generations and faster growth.
To visualize this, watch one of those speeded-up videos of starfish and sea urchins. At our pace, they are sedentary. At their pace, it's Thunderdome all day every day.
Your example doesn't require an invasive species. Aggressive species (ones with their consumption and reproduction clocks set "too high") can arise through mutation, too. In either case they spread like cancer and usually take down parts of the ecosystem with them before they are finally selected against. Eventually, ecosystems find mechanisms to limit the damage of cancer-like species and adjust everyone's "clocks" to appropriate levels. Ecosystems that cannot bring their species into stasis experience repeated shocks, are less stable than ones that do find stasis, and often disappear. This is exactly why the long arc of evolution is best understood as a punctuated equilibrium (https://en.wikipedia.org/wiki/Punctuated_equilibrium) rather than a constant drift. Systems that find stasis are more successful than ones that don't. Unfortunately these systems are repeatedly interrupted by drastic environmental changes like geological events. So, the systems that survive are the ones that tend toward balance but are able to adapt to occasional disruptive events. That requires biodiversity that is generally reduced by aggressive species.
> To visualize this, watch one of those speeded-up videos of starfish and sea urchins. At our pace, they are sedentary. At their pace, it's Thunderdome all day every day.
Or look at hardwood forests that develop extremely slowly over thousands of years, despite the availability of plenty of energy from the sun. The slower the system, the better it actually proves my point. Clearly, evolution does not select for the fastest growing, most aggressive species out there. Otherwise starfish and sea urchins would move faster, or be displaced by something that moved faster.
Properly understood, ecosystems are super organisms that require many many moving parts to bootstrap, grow and function. Human bodies are analogous. Your cells aren't trying to "outcompete" every other cell in a Thunderdome situation every day. They are carefully regulated both internally and externally. When those regulatory mechanisms fail, you end up with cancer and you die. Clearly, cell replication rate is a key regulator internal to a cell that prevents us all from experiencing runaway cancer and dying. Clearly ecosystems have species with internal regulation mechanisms as well.
Of course, like many ancient traditions this looks completely different in modern times.