Inheritance and Variation of Traits | Science
The study of genes, traits, and inheritance is important in the life sciences field. As you advance your studies in preparation for the TASC Test Assessing Secondary Completion™ Science subtest, be sure to read our blog post on what you need to know about heredity. Once you understand the history and basics behind heredity, let’s take a deeper look at this subject and discuss how traits are inherited and how they vary from generation to generation.
Variation and Inheritance Overview
Organisms of any given species are almost never exactly the same. From small organisms like ants and pill bugs, to large organisms like human beings and gorillas, differences in size, color, health, wellness, personality, and many other traits, emerge from offspring to offspring.
Think about this: You may resemble one or both of your parents – and even grandparents – but you do not look exactly like any of them. You may have your dad’s hair color and your mom’s eye color, or you might not have either of your parents’ eye colors. It all depends on how you inherited certain traits.
According to the American Museum of Natural History, inheritance and trait variations are “often the result of random mutations, or “copying errors,” that arise when cells divide as new organisms develop.”
The scientists at AMNH explain that when organisms reproduce, their DNA is passed on to their offspring. Because traits are encoded in DNA – the set of instructions encoded in living cells for building bodies – offspring inherits variations of their parent’s traits. For the most part, trait variations do not change too much. For example, dogs with long hair tend to have puppies with long hair.
The Theory of Natural Selection
As you learned in the blog post on heredity, Charles Darwin and Alfred Russell Wallace were the first scientists to announce the theory of natural selection. Darwin speculated that members of individual species competed against one another for resources and for mates, especially as their populations grew. Because of variations in traits, some organisms are better able to compete and get the resources they need. The less-competitive organisms, and their less-competitive traits, die out over time.
Competitive vs. Less-Competitive Traits
If less-competitive organisms die out over time, how do less-competitive traits, or recessive traits, keep arising in species?
If only dominant traits are passed on over time, shouldn’t there only be competitive organisms left?
The simple answer is: no, there cannot only be competitive organisms left at this point.
Though scientists argue that evolution has always been going on (because through evolution, we get the species we have on Earth today, rather than the ancient creatures who used to live on this planet), the process of evolving has not completely eradicated undesirable traits. This is primarily because what is desirable and what is not desirable changes over time depending on the organism’s habitat, needs, and other factors.
For example, as Richard W. Young explains in the Journal of Anatomy, scientists have proposed that early humans began as chimpanzee-like apes. They developed the need to throw rocks and swing clubs at their enemies and their prey, and these skills became essential to survival. These skills “yielded reproductive advantages for millions of years, driving natural selection for improved throwing and clubbing” which caused the human hand to adapt to these skills.
Because the hand evolved, and early humans developed the use of opposable thumbs, they were eventually able to develop hunting and gathering skills. Early humans without opposable thumbs died off. If they hadn’t needed thumbs to compete against enemies and hunt prey, they probably wouldn’t have developed them – and the human race today would look much different.
Evolution is a Long-Term Process
At early points in our history as a species, our needs changed. Opposable thumbs began to be inherited as those individuals became more and more competitive.
This is not to say, however, that after one generation, humans without opposable thumbs were gone. It’s important to note that because traits vary, and because some organisms inherit recessive traits, it can take many generations – sometimes thousands of generations – for traits to be removed from a species.
As humans, we are still evolving. We just can’t see the impact of it in the short term.
Variations in Traits Can Be Tiny
The American Museum of Natural History (AMNH) points out in its discussion of Selection: Survival and Reproduction that “small variations can influence whether or not an individual lives and reproduces.” For example,
- An organism’s color can mean the difference between camouflaging itself or being seen by predators.
- Sharper eyes and claws help organisms find and catch food.
Brighter coloration on a male organism can improve its chances of attracting a mate.