Sidebar - October 2010

Mammal-like Reptiles

What would make a reptile like a mammal? It would be mammal-like if it had mammary glands; but mammary glands donít fossilize. It would be mammal-like if it had a womb; but wombs donít fossilize. It would be mammal-like if it had hair instead of scales; but none of the mammal-like reptile fossils had skin impressions. It would be mammal-like if it were warm-blooded; but body temperature doesnít fossilize.

The only things mammal-like about mammal-like reptile fossils are three bones in the jaw which look like the three bones in the mammalian inner ear. According to some evolutionists, these bones accidentally grew in the ear instead of the mouth, and provided an improvement in hearing which increased their chances of survival.

Any engineer who has ever designed an antenna, microphone, loudspeaker, or any other component that depends upon impedance matching, knows how silly this is. The three bones in the middle ear use leverage to match the impedance of the fluid in the ear with the impedance of air outside the air to allow the transmission of sound waves.

You may not know about impedance, but you have probably been to a public swimming pool with a crowd of people at some time in your life. As you stood there on the diving board, you could hear all the laughing and conversation going on. As soon as you dove in, you could not hear those sounds from the surface, but heard underwater sounds (gurgling and splashing) that you didnít hear when you were on the diving board. The reason has to do with impedance matching.

The density of water is much higher than the density of air. Sound waves traveling through low-density air are reflected off high-density water. Sound waves traveling through high-density water are reflected off low-density air. The density of the medium (air or water) impedes the wave motion to a particular degree. It is a fundamental property of waves that they donít pass from one medium to another unless their impedances match.

Your radio needs an antenna because the antenna is designed to match the impedance of the air with the impedance of the electronic circuitry of the radio, allowing waves to pass in and out of the radio. In the same way, the bones in your ear use mechanical leverage to match the impedance of the fluid in your ear to the impedance of the air surrounding your ear. Without those bones, the sound waves would just bounce off your eardrum like sound waves bounce off the surface of a swimming pool.

Designing antennas (and microphones and speakers) is tricky business. They donít just spontaneously occur in nature. It is unreasonable to think that jaw bones that happened to grow in the wrong place would just happen to function as efficient impedance matchers.

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