How do scientists explain the evolution of the human brain?
As with other complex biological features, scientists explain the evolution of the human brain through natural selection. However, the human brain presents some unique challenges that must be answered through slightly different methods. There are aspects of the brain of homo sapiens that do not fit Darwin's usual pattern. The time scale allowed for significant change is shorter. The mental capabilities of humans are far above other organisms. The unique nature of man puts our brain in a class by itself.
Scientists explain the apparent change and diversity of most biological systems through naturalistic evolution. The generally accepted theory is that small, random changes in an organism sometimes provide an advantage. This advantage allows the organism to be more successful than those without that "upgrade." Soon, the "upgrade" becomes the norm, and eventually another random mutation will occur. Over millions of years, this results in a completely different organism.
Scientists have experienced problems when applying the normal methods of evolution to the human brain. Paleontologists and neurologists have noted that there is little to no notable difference between the brains of modern humans and so-called Neanderthals, other than a slight change in size. Given the supposedly significant differences in intelligence, social structure, and physical features, this seems strange. Those studying this field admit as much. The coordination required between the brain and the body is another. The development of the human brain is one of the biggest unsolved mysteries for evolution.
The response used by scientists to explain the evolution of the human brain involves a "fast evolution" scheme. Researchers at the Howard Hughes Medical Institute concluded that the human brain evolved very rapidly. Their research led them to believe that there was considerable "selection pressure" to evolve the brain into a larger, stronger unit. As human society became more sophisticated, the advantage of a larger brain became more pronounced. This caused the evolutionary process to accelerate, resulting in a quick progression to modern man.
There are some unanswered aspects to these theories, however. As with most other evolutionary studies, there are plenty of reasons given for why a larger, stronger brain is useful, yet no actual biological or physical explanation for how it occurred. It is important to realize that modern science has never observed a beneficial, inheritable mutation that causes a permanent change in a species. Variations from a norm have survived a few generations, but then have swung back to the original form.
The idea that the usefulness of the brain caused evolution to accelerate also seems improbable. If the advantage was very strong, it would seem more likely to see a very clear, steady, uninterrupted evolution. Just because a feature is useful should not make a mutation more likely. To assume that mutation occurred more frequently because the larger brain was "needed" implies intent and intelligence behind the process.
Finally, aligning the development of the brain with the development of the body poses a massive problem for evolutionary scientists. Simply looking at a possible evolutionary event brings the dilemma to light. Imagine a mutation, or series of mutations, that improve the eyesight of an organism. For the brain to be able to process this information, it either must evolve after the eye, before the eye, or at the same time.
Evolving the brain after the eye means that the eye's function is not immediately usable, and so cannot be an advantage. Also, the likelihood of a random brain mutation granting use of the new ability is low once, let alone for millions of mutations over billions of years. Evolving before the eye is similar, in that the brain would have wasted time, growth, and resources on something not useable. This would be a disadvantage, which natural selection indicates is a sign of impending extinction.
Evolving the brain at the same time as the eye is the only explanation that allows the function to be an actual advantage. However, simultaneous mutations in the eye and brain that work together to provide an advantage cannot be expected to occur repeatedly in every species on earth. There is no doubt that this would be a useful event, but that is not an explanation for how it could happen.
Even the terminology used by scientists to explain the evolution of the human brain sounds anything but random: The homo sapiens brain evolution was a "special event." Rapid evolution was "needed." The brain evolved "in preparation" for our complex social structure. Even those dedicated to a random, naturalistic explanation for life cannot avoid using terminology that implies purpose, intent, and intelligence.
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