I like the comparison, but with aviation on a fundamental level we made it simpler (removing actuation), not added more (senses we dont need)

Jet engines do not strike me as being inherently simpler than muscles, not by a long shot.

They're still the best way we know of going about the business of building a flying machine, for various reasons.

Piston engines surely are more complex than jet engines though? Which replaced the "flapping engines".

They are not. Turbine engines require much higher quality manufacturing and tolerances and operate at much higher speeds and pressures. There is more to it than the perceived number of moving parts.

I'm not sure I agree. I think just having wings that flex a bit is mechanically simpler than having an additional rotating propellor. After all, rotating axles are so hard to evolve they never almost never show up in nature at a macro scale. Sort of a perfect analogy to lidar actually. We create a new approach to solve the problem in a more efficient way, that evolution couldn't reach in billions of years

Rotating axles have not evolved in animals not because they were complex, but because any part of an animal requires permanent connections with the other parts, not only for the supply with energy but also for the continuous repairing that is required by any living body, to avoid death.

Artificial machines rely on spare parts manufactured elsewhere, which are used by external agents to replace the worn out parts.

For an animal to have wheels, it would have to grow wheels in some part of the body, periodically, then use its limbs to detach the wheels and attach them on the axles, after removing the old wheels. This is something sufficiently complex to be extremely unlikely to appear from evolution.

Even this huge complication would be enough only for passive wheels. For active wheels there exists no suitable motor, as the rotational motors with ionic currents are suitable only for the size of a bacteria. All bigger living beings use contractile motors, which cannot be used for a rotation of unlimited angle. So active wheels would also need a different kind of motor, which can work without a solid connection between the 2 moving parts. The artificial motors of this kind use either electromagnetic forces or fluid expansion due to temperature or pressure variation. Both would be very difficult to evolve by a living being, though electric fish and bombardier beetles show some possible paths.

Living beings are not devoid of axles and wheels; rather, they are entirely composed of them, at scales and in forms compatible with biology.

At every relevant level, life relies on rotating and cyclic structures coupled through continuous material exchange. The objection to wheels in animals assumes that axles and wheels must be rigid, permanently isolated parts. Biology does not work this way. Instead of discrete components joined once and preserved unchanged, living systems implement rotation through structures that are simultaneously connected, repaired, and replaced.

Cells are full of rotary and quasi-rotary machinery. Flagella are true rotating motors with stators, rotors, bearings, and torque generation via ion gradients. ATP synthase is literally a wheel-and-axle device, converting rotational motion into chemical energy and back again. The fact that these devices operate at molecular scale does not make them conceptually different from macroscopic axles; it shows that evolution favors rotation precisely where continuous repair and material flow are required.

At larger scales, joints function as constrained rotational interfaces. Hips, shoulders, knees, and vertebrae are axles embedded in living bearings, lubricated, rebuilt, and reshaped throughout life. Bone remodeling, cartilage regeneration, and synovial fluid circulation solve the very problem claimed to prohibit wheels: permanent connection combined with continuous maintenance. The difference from artificial machines is not the absence of rotation, but the absence of rigid separability.

Even limbs themselves behave as compound wheels. Gait cycles convert linear muscle contraction into rotational motion around joints, then back into translation. Tendons wrap around bones as belts around pulleys. Muscles do not rotate indefinitely, but unlimited rotation is not a requirement for a wheel; it is a requirement imposed by certain human machines. Biological wheels rotate as much as function demands, then reverse, exactly as many engineered systems do.

The claim that active wheels require exotic motors overlooks that biology already uses fields and flows. Ionic gradients are electric fields. Blood pressure, osmotic pressure, and gas expansion are fluid-based actuators. Electric fish demonstrate macroscopic bioelectric control, and insect flight shows that indirect actuation can drive cyclic motion far from the muscle itself. The distinction between electromagnetic motors and biological motors is one of implementation, not principle.

What evolution did not produce is a detachable, externally replaceable wheel, because life does not outsource maintenance. Instead, it internalizes repair, redundancy, and gradual replacement. From this perspective, an animal is not a wheeled vehicle lacking wheels; it is a dense hierarchy of axles and wheels whose boundaries are soft, whose materials are alive, and whose motion is inseparable from their growth and repair.

Life did not fail to invent wheels. It dissolved them into itself.

Most of what you have said is not different from what I have said.

All the rotating parts bigger than some tens of micrometers have only a limited rotation angle, where the limits are enforced by the solid connections between the 2 mobile parts, e.g. tendons, nerves and blood vessels.

The bacterial flagella and the rotating enzymes, which are powered by ionic currents, cannot be scaled to greater sizes. Already the flagella of nucleated cells (eukaryotes) are no longer based on rotating motors, but on contractile proteins, which must be attached at both ends on the mobile parts, limiting the relative movement.

Unlimited rotation is an absolutely necessary condition for a wheel that is used in locomotion, otherwise it is no longer a wheel.

A wheel used in locomotion that would have limited rotation would be just a leg that happens to have the shape of a wheel, because like a leg it would have to be raised from the ground for the forward motion, eliminating the exact advantage in efficiency that wheeled vehicles and tracked vehicles have over legs (i.e. that backward and forward movement are simultaneous and not separated in time during a step cycle, and no energy is wasted with a vertical oscillation of the leg).

What counts is the overall complexity, not the complexity of a single subsystem.

Using more senses allows simpler processing of the sensor data, especially when there is a requirement for high reliability, and at least until now this has demonstrated a simpler complete system.

I would posit that the human brain is complex, and adding senses is simpler than replicating an aspect of the mind more accurately.

Others in this subthread discussed the comparison of the complexity of different ways of achieving flight itself, but I think there is an interesting discussion in that... well... we do add senses we don't technically need to achieve stable flight (but are very useful for safe flight and have reduced the incidence of aviation incidents and accidents dramatically).

Whether it be altimeters based on radio[1] or air pressure[2], avoidance and surveillance systems that use radio waves to avoid collisions with other aircraft[3][4], airborne weather radars[5], sensors that measure angle of attack (AoA), GNSS location, attitude, etc, many aircraft (even unpowered gliders!) have some combination of special sensing systems that aren't strictly necessary to take off, fly to a destination, and land, even if some are required for what many would consider safe flight in some scenarios.

Many of these systems have redundancies built in in some form or another and many of these systems are even built into unmanned aerial systems (UASes) big and small.

[1]: https://en.wikipedia.org/wiki/Radar_altimeter

[2]: https://en.wikipedia.org/wiki/Pressure_altimeter

[3]: https://en.wikipedia.org/wiki/Traffic_collision_avoidance_sy...

[4]: https://en.wikipedia.org/wiki/Automatic_Dependent_Surveillan...

[5]: https://skybrary.aero/articles/weather-radar

How many of these are due to going outside the normal envelope of what birds do?

> easiest

This is the keyword here, just because the other approach is harder does not mean it is impossible.

It's a decent gamble to try and do things the hard way if it is possible to be deployed on cheaper/smaller hardware (eg: no lidars, just cameras).

Is it still a decent gamble after you've been trying (and failing) for a decade, and numerous well funded competitors are going the easy way, and when there is huge upside to being first, and when the value of FSD easily covers the rapidly falling cost of LIDAR?

No. It's not a good idea. It's not a good gamble. It's stupid, and the engineers can see it's stupid. A lot of them have quit, reducing the very slim chances of it working even further.

But why is FSD "failing" is the key question.

Hint: it's not the sensor inputs that are the bottleneck!

Yeah you could be right.

Not my area of expertise, so I’d rather not try to predict what will work and what won’t.