Why it would not be common ?

Question

Here is a para

"Anatomical bilateral symmetry is a common trait. It follows, therefore, that it confers survival advantages on organisms. After all, if bilateral symmetry did not confer such advantages, it would not be common".

i could not understand the meaning of the above.

How Anatomical bilateral symmetry confers survival advantages on organisms ? can anybody light on it ?

"if bilateral symmetry did not confer such advantages, it would not be common"

why it would not be common ?

Answer 1

I should add to the previous answer that only traits that are heritable (i.e., genetic) apply. Once in a while, mutations occur in a population. Depending on the specific circumstances of the environment at that time, the novel trait can be either advantageous or disadvantageous. If it is disadvantageous, then the individual(s) bearing that trait would be less successful at surviving and reproducing, that is, it dies before it can reproduce any or many offspring. (No offspring means no individual carrying the unsuccessful trait in the next generation.) If the trait confers some advantage to the organism that makes it more likely (compared to others in the population) to survive and reproduce, that organism reproduces. If the trait is genetic/heritable, that same trait appears in some or all of its offspring. If the trait continues to be advantageous, it will continue to be passed on genetically from generation to generation, making it more common. In some cases, the trait is so advantageous compared to the alternatives available thus far that all members of that species carries it.

Answer 2

"Anatomical bilateral symmetry is a common trait. Therefore, it must help animals survive better. After all, if it didn't help them survive, it would not be common."

They are saying that if a trait does not help an animal survive, that animal will die and not pass on that trait. But if that trait does help the animal, they will survive and pass on that trait. Therefore traits that help animals survive are common, but unhelpful traits are rarely seen (in live animals, anyway).

"It follows" is the same phrase as "therefore." "Confers" means "pass to the next person" or "endow."

I hope that helps!