In Christopher McDougall's book about running, which I think launched the chia pudding trend, he has a story about a researcher whose theory is that bipedal motion separates breathing rhythm from gait when running. A quadruped has to breathe in time with their gait, because internal organs push forward into the diaphragm when the front feet land. According to the researcher, this is my jogging humans can stay cool while chasing quadruped prey, which are pushed to overheating and exhaustion.

I once heard that a springbok is a much better long-distance runner than other animals because it breathes automatically while it runs. The running motion directly powers the breathing motion, making it use less energy.

I can't find a quick source to back this up, though.

I never thought about that. I wonder why it hasn’t evolved more often then? Basically limited to humans and birds. (I guess kangaroos too?)

Many animals are occasionally bipedal. Apes and monkeys and similar of course.

But also bears and no doubt many more.

Domestic cats will stand up on their hind legs to see further.

Not of those are efficient runners in that position, though. It's a careful balancing act.

Speed vs. endurance. Depends on which is more valuable in a given environment.

Predation leads to optimising for speed. Calorie cost isn't such an issue if one is either getting a meal or avoiding being a meal immediately the sprint is finished.

Even within ancient to medieval cavalry this tradeoff existed; the horse one rode to the battle would often not be the same breed as the horse one rode in the battle.

(cavalry having arisen in the first place because a slow horse is still much faster than a fast man. infantry that can't run can't regroup)

Two critters threw a monkey wrench into that machine. We're one of them, canids are the other. Persistence hunting is a thing. Let them sprint; they'll have to sprint again when we get there. Sooner or later, they won't be able to sprint anymore.

Fast men are very competitive with horses over long distances [0]. Horses have other advantages like being able to carry more weight and live off grass.

[0] https://en.wikipedia.org/wiki/Man_versus_Horse_Marathon

> Fast men are very competitive with horses over long distances [0].

This might be true, but the citation says the opposite:

> In 2013, extensive forestry works meant the organizers had to modify the route considerably, resulting in a course of nearly 24 miles, instead of the usual route of just under 21 miles. Despite a very hot day, the longer and hillier course favoured the horses, with 2011 winner Beti Gordon comfortably beating the first man, Hugh Aggleton.

> Following a number of criticisms of the extended course in 2013 and 2014, the course for 2015 was shortened back towards 21 miles. This provided a more even match between man and equine

Men win sometimes, the fastest man is generally within 20% of the fastest horse, and the fastest man beats plenty of the horses. The fact that minor differences in length, weather and terrain are significant to the result is also more than enough to say the men are competitive.

But what the article says is that longer courses favor the horses. We can't just define "long distances" to mean "exactly 21 miles". "Humans are competitive with horses over long distances" is a terrible way to phrase the idea that the advantage of horses grows with increasing distance.

Consider that cavalry wipes the floor with infantry in terms of how much ground can be covered in a day. Don't think soldiers are selected for speed? Consider also that we have an inscription from an Egyptian pharaoh commemorating the excellence of his soldiers, as measured by the speed of their march.

33 km is much longer than I was talking about (and lends evidence to the sibling thread's persistence hunting); I'm guessing most cavalry pursuits of routed infantry would've been between 1 and 10 km.

Taking world record 5k (5000m/12.58min) ~= 400 m/min

versus a top CCI run (6398m/9.97min) ~= 640 m/min

we see that at these shorter distances the horse has a distinct advantage.

https://www.youtube.com/watch?v=IEFeZuc3J3g

Then why do four legged animals still exist? Especially animals that walk a lot. Elk, wolves, etc...

They can reach higher top speeds.

Could be misremembering but I recall reading that bipedalism in humans correlates with a narrowing of the birth canal, potentially increasing mortality during childbirth and also selecting for infants that are underdeveloped compared to other newborn mammals.