119. How Humans Evolved

28 Aug

The latest issue of Scientific American (September 2018) is concerned with the issue of how we humans are different from other animals. The issue title is: “A Singular Species: The Science of Being Human.” A lot of this valuable issue is concerned with evolution. As I looked through the issue, I tried to find a discussion of certain details about how evolution actually produced our superior brains.

Here is my analysis.  First, what is necessary for biological evolution is the following:

1. Death, which leads to many generations, that can make small incremental changes.

2. Mutation: A change in DNA that is relatively permanent.

3. Survival of the fittest. The key to understanding “fittest” is that there is a combination of traits in an individual that will allow him (and her) to reach the age for sex and child rearing. The mutation and progeny must live long enough to promote the reproductive cycles. These are the main themes, but many details are involved in the whole process of evolution.

An overall observation, is that evolution is a tree process rather than a number of parallel lines. Some detail about primates is instructive. Primates include lemurs, lorises, monkeys, apes, and man. All primates are mammals and have advanced binocular vision, grasping ability, and specific enlargements of brain.

60 or 80 million years ago there was a key species that had the capability of leading to various primate species. There are many primate variations that have been successful. Some species will continue because they are “fit” and those less successful may terminate, that is, become extinct. The branching tree of evolution will lose some branches and gain new ones. The species we see today, have all been good at all the many requirements for survival. The lemurs, monkeys, apes, etc are all successful variations.

The interesting fact is that perhaps a hundred million years ago, a mutant was born that had a DNA structure that could eventually lead to the evolution of humans. I think the existence of humans was not inevitable, it was just a chance event. If you look at all the other current species, many non-human animals are quite successful. Humans are not necessary for their success, and in fact, humans have been responsible for the extinction of many interesting animals. It is easy to imagine an earth without humans.

Some precursor animal lived in an environment where mental ability was a major asset. So this species kept evolving better and better brains that led to more successful and likely reproduction.

Let’s fantasize an environment where high intelligence, instead of such traits as better legs for running, was important for survival. Suppose one such environment was characterized by several major changes in food supply. Perhaps a favorite plant or animal to eat became extinct. The adaptation to major changes in food source probably would require more brain power. There could also be major changes in climate or the availability of water. Perhaps in one region there were two pre-human species that were highly competitive for a limited supply of food. The smarter species could have been more able to survive, and more likely to pass its DNA on to future generations. A superior memory could help find water during a drought, or the location of food sources for different seasons.

Dinosaurs never developed big smart brains like ours during their many years of existence. This suggests it takes a certain DNA structure and a certain environment to initiate the evolution of this large adaptive brain. It may, in fact, be a very rare occurrence in the Universe, and we are just very lucky.

I have written the above to provide information in a short form that may be useful for those not wanting read thousands of book pages. It is an effort to present key facts that may be lost in a sea of writings. I also commend the thousands of dedicated scientists that have contributed to our understanding of this profound topic.

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