In 1859 Charles Darwin published his book On the Origin of Species. In it he formulated his scientific theory of evolution by natural selection. The theory of Evolution states that changes in species occur through the process of natural selection. With each generation of creatures, more offspring are produced than can possibly survive. Those that survive long enough to pass their genes along dictate the future of the species. In general, the following three facts guide the evolution of future generations:
- Phenotype Variations – traits vary among individuals with respect to morphology (physical form), physiology (biochemical), and behavior.
- Biological Fitness – Some traits lead to longer survival and/or more reproductive success, some lead to shorter survival and less reproductive success.
- Heritability – A specific trait’s ability to be passed from generation to generation within a population. This higher heritability can come from a newly evolved trait that gives an advantage in the current environment, or it can come from a change in the environment giving long ago evolved traits an advantage.
Traits that lead to a shorter life or less reproductive success are replaced with better traits. Over generations, the progeny of parents better adapted to survive and reproduce in a specific biophysical environment will increase in numbers within the population. The traits that lead to more biological fitness and higher heritability will replace other traits over time. This teleonomy is the quality whereby the process of natural selection creates and preserves traits that are seemingly fitted for the functional roles they perform.
Over many generations a new species can evolve. Sometimes a population of creatures migrates or gets cut off from it’s kinship. That isolated population may end up in a different environment either because they migrated or because the environment changed. Traits suitable for a specific environment will win out over other traits. For example, camels adapted over time to an environment where there is little water available for long periods of time. Camels can go more than six months without drinking water. Contrary to popular belief, the hump does not actually store water, it stores fat. The excess fat helps the camel survive over six months without water.
To illustrate some evolutionary concepts, let’s imagine a population of camels in an environment where water is readily available. Where the excess fat hump no longer has an evolutionary advantage. What will happen? Will the hump go away over many generations? The answer is, no one knows! It might. It might not. The variation in traits within a population is random. The hump may never vary even over millions of years. Or, a set of camels could be born with smaller humps that gives them an advantage. Perhaps there could be a mix of sizes of humps within the population. Under this scenario, if you put the population back in an environment with little water, the larger hump camels are likely to win out. Or not depending on the biological fitness and heritability of the competing traits. The point is that there is no greater scheme. There is not a guiding hand deciding what traits a population should receive. It’s guided only by nature.
Evolutionary differences will occur even with two populations in similar but isolated environments. The randomness of the evolution of phenotype variations, traits, can lead to differences in populations. For example, Darwin’s finches inhabiting the Galapagos islands are a good example of an isolated population adapting to it’s environment. Over about two million years, the finches on the Galapagos islands developed blunt or pointed beaks suitable for their environment.
Whether a set of traits is newly evolved or the environment changed, the differences in traits within a population can lead to a new species. However, there is no set rate of evolution. A new species can evolve fairly quickly once a set of traits gives them an advantage in a given environment, or not. A given species may last many millions of years, or just a few thousand years. For example, the horseshoe crab of today is essentially unchanged from 445 million BCE. The nylon-eating bacteria Flavobacterium species has existed on Earth only since about 1940.
Up until modern times humans generated a new species of homind about every 150,000 years which is about every 6,000 generations1. Prior to the invention of airplanes, getting to distant locations was difficult and in many cases impossible. Human populations were isolated. The human genome was evolving within each isolated population. Those new and evolved traits over the last 30,000 years are well documented. The website 23andme.com focuses on 23 chromosomes that identify the ancestors of most modern humans prior to modern civilization.
A final note on the future of human evolution. Because humans all over the world mate with each other regularly, I predict the next time we can be isolated from each other long enough to evolve into a new species of hominid is when a population of humans migrates to another planet. The wild card in all this is modern medicine which keeps people with unfavorable traits alive long enough to procreate. Also, modern medicine has brought us gene editing. We have the ability right now to create super humans with many superior traits. For an interesting take on the future of gene editing, I recommend reading the book “Homo Deus” by Yuval Harari.
- This is my guess as to how frequently hominids evolved into new species over the last 1 million years. It is just a guess used to illustrate. It is based on what we know of the beginnings of various hominids like Homo Heidelbergensis, Neanderthals, and Denisovan. Homo Heidelbergensis emerged perhaps about 700k BCE. Neanderthals perhaps about 400k BCE. Denisovans perhaps about 300k BCE.