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Similar structures for similar functions, different for different (Talk.Origins)

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Response Article
This article (Similar structures for similar functions, different for different (Talk.Origins)) is a response to a rebuttal of a creationist claim published by Talk.Origins Archive under the title Index to Creationist Claims.


Claim CI141.1:

Similarity of structures in different life forms reflects the fact that they were created for similar purposes. Different structures reflect different functions.

Source: Morris, Henry M., 1974. Scientific Creationism, Green Forest, AR: Master Books, p. 70.


CreationWiki response: (Talk.Origins quotes in blue)

1. Actual known designers use similar forms for similar functions and different forms for different functions.

True, but they are not exclusive.

  • Similar functions can have differences, that can cause differences in form.
  • Different functions can have similarities, that can cause similarities in form.

In life, we often see different forms for similar functions (e.g., different designs for bird, bat, and pterodactyl wings)

Talk Origins is ignoring the differences in these animals in terms of size and mode of flight. While all three types of wings are designed for flight, both the mode of flight and size of animal are different. These differences requirer some differences in design.

similar forms for different functions (e.g., spider webs for trapping flying insects, reinforcing tunnels, protecting eggs, transferring sperm, ballooning, marking a trail, serving as a safety line after jumping to escape a threat, and detecting motion).

Actually these spider webs do have the same function: construction material. They may be used to construct different things, but they are still construction material.

Consider four piles identical bricks. Their form is identical because they all serve the function of construction material. However they are used to construct different things: a house, a wall, steps, and fire place.

The same thing applies to spider webs, they all serve as construction material but are used to constructed different things. Furthermore the fact spiders are preprogrammed to be able to use web material for such tasks itself suggests that spiders were designed.