Evolution Icon Evolution
Intelligent Design Icon Intelligent Design

New Research: Stuart Burgess Demonstrates the Exquisite Engineering of Human Limbs

In my last three articles (hereherehere), I described the research published by engineer and biomimetics expert Stuart Burgess on the exquisite design of vertebrate limbs. His analysis demonstrates why the similarities between vertebrate limbs is better explained by design than by common ancestry. In the journal Biomimetics, Burgess recently published another article, “How Multifunctioning Joints Produce Highly Agile Limbs in Animals with Lessons for Robotics,” that is featured on its cover. It further demonstrates that human limbs were designed.

Multifunctioning Limbs

The article explains how the multifunctional capacities of the human wrist, knee, and foot are optimized for the diverse motions that humans perform. It overturns claims that human limbs display poor design (herehere), and it provides positive evidence for design by demonstrating how our limbs represent the best construction possible to meet our needs. 

Burgess describes how the ability of our limbs to perform multiple functions leads to their optimal performance for diverse tasks:

Multifunctionality is a very advantageous design feature because it reduces the number of subsystems and components and produces a compact design. Multifunctioning in joints leads to a high degree of compactness which then leads to a host of benefits such as low mass, low moment of inertia and low drag. It also leads to reduced energy demands and the ability to meet tight dimensional constraints. Multifunctioning joints also have the additional benefit that it often enables the animal or robot to perform multiple high-level functional tasks.

Required Fine Tuning 

Burgess details how multifunctioning limbs must meet exacting engineering constraints in such features as integration, reconfiguring during movement, and miniaturization:

The parts of the knee joint are highly integrated, especially the meniscus in the way it surrounds the condyles. Joint locking and unlocking represents reconfiguration. To unlock the joint, the tibia is made to rotate internally by flexion muscles, especially the popliteus muscle behind the knee, as shown in Table 2. Like the wrist joint, there is miniaturisation in the sensors, nerves, blood vessels and lubrication system that helps to achieve compactness. The layout of the knee joint represents a unique solution where the layout performs multiple functions with multiple aspects of fine-tuning and integration.

Meeting the numerous constraints requires high levels of fine-tuning: 

The requirements of multifunctioning are so exacting that fine-tuning of design is also generally required, such as the common centre of rotation in the wrist (Section 2), the geometry of the cruciate ligament 4-bar linkage in the knee (Section 3) and the precise alignment of the medial arch with the talus bone in the foot (Section 4). Therefore, it can be expected that fine-tuning is required for robotic multifunctioning joints. Indeed, this was the case for the three bioinspired designs presented in this paper for the wrist, knee and foot.

Challenge to Evolutionary Theory

Burgess describes why multifunctioning limbs are difficult to explain by evolution since they require irreducibly complex sets of components:

Complexity in biological systems is sometimes labelled as an emerging property. However, it is very difficult to explain how a multifunctioning system could emerge from an initially single-functioning system because the first single-functioning system would have to be one of the very few solutions that could lead to a later multifunctioning system. When discussing the origin of mechanical linkage mechanisms in animal joints, Muller has stated that it is very difficult to see how complex mechanical linkage systems can be developed in a bottom-up step-by-step process. Therefore, multifunctioning in biological systems such as limb joints presents a major challenge of irreducible complexity for evolutionary biologists.

Burgess’s research represents yet another nail in the coffin of the standard evolutionary model. It also further demonstrates how a design framework is required to understand the higher-level organization of animals.