Many proponents of intelligent design (ID) claim that life is too complex to be the result of natural processes, and therefore must’ve been designed. To this argument I have the following responses:
1) Even if the complexity of life were unexplainable by evolution, it wouldn't give evidence of design.
2) Complexity is not the same as design. There are simple things that are designed and complex things that arise naturally (cave formations, weather patterns).
3) In known designs, innovations that occur in one product quickly get incorporated into others, but in eukaryotic life, innovations stay confined to one lineage.
4) In design, form follows function. Yet life shows examples of different forms with the same function (differing wings of birds, bats, insects, and pterodactyls), as well as similar basic forms with different function (same bone patterns in human hand, whale flipper, dog paw, and bat wing). This shows that life lacks a plan; there are no optimal specifications for living processes and structures.
5) Life is indeed complex, but doesn’t design aim for simplicity?
6) In almost all designs, the manufacturing process is separate from the design itself. Living things replicate themselves.
7) Life is wasteful. Many organisms do not get to reproduce, and most fertilized eggs die before growing much. Good design would minimize this waste.
8) Life itself shows poor design. There are parts that were jury-rigged out of other parts that were used for another purpose. The result is a form that is functional but is not optimal (many organisms have parts that are not even functional!). This is what we would expect from evolution, not from intelligent design.
9) Evolution itself can be considered a design process, and the complexity and arrangement we see in life is much closer to what we would expect from an evolutionary, accumulative design process than a purposeful, intelligent designer.
10) Some systems, like a cell or the human body, are irreducibly complex, meaning that if you remove one certain part, the whole system fails. But contrary to creationist argument, irreducible complexity shows a lack of design. For the designer’s purpose of keeping the creature alive, you would not want systems that would fail if any one part fails. You would want a robust system.
11) If complexity in life indicates a designer, then what about non-living things? Rocks and lava aren’t complex. Neither are solar systems and galaxies. These things are simply collections of matter mindlessly following natural laws. If complexity and purposefulness truly indicate a designer, does simplicity and purposelessness indicate no designer?
12) There are several evolutionary mechanisms that can result in irreducible complexity: deletion of parts, addition of multiple parts (sometimes accidental replication of entire systems), change in function, and gradual modification of parts. These observed mechanisms make irreducible complexity completely plausible.
Claiming intelligent design of the universe based off of life’s complexity and functionality has no ground to stand on. Combine that with the complete lack of evidence, predictions, and scientific research that ID has generated, it is safe to say that ID is a belief based on religious theology, not on evidence.