[WhompingWindows]

It already has: hip/knee replacements, surgeries to repair where human body couldn't do so well, antibiotics to supplement the immune system, immune-boosters to boost it, iodine added to salt, sunglasses, sunscreen... There are literally hundreds of ways science is adding to our evolution by improving our bodies' biochemistry.

[Pulcinella]

I’ve heard Titanium (like used n joint replacements) is actually weaker than bones. It’s better than not having the surgery, but you are not Wolverine.

[jjk166]

You can't really compare bone and titanium in terms of strength. Bone is strong in compression but weak in tension and extremely weak in shear. Titanium is slightly weaker in compression but dramatically stronger in tension and shear.

Bone works great until it fails catastrophically (ie it fractures, breaks, and shatters) while titanium will begin bending long before it breaks. The latter is generally preferred in engineering structures, but since a human can heal its bones, the sudden failure is an acceptable compromise for consistent performance even at high loads.

Finally, bone weakens as we age, as does the body's ability to heal itself. Eventually wear and tear will make joints highly uncomfortable and the potential damage from otherwise minor injuries significantly greater. Titanium holds up well in the body over human timespans, and our ability to replace titanium components far exceeds our ability to artificially regenerate bone.

There are good reasons why evolution favored a composite like bone for our structural elements, but if you could magically replace your skeleton with one made of titanium once you were past your prime, it would be an unambiguous upgrade.