As we’ve learned in previous tutorials, natural selection is the primary mechanism
by which biological evolution operates.
We typically envision this system as favoring the organisms who compete the most effectively
in order to survive and reproduce.
However, natural selection does not always operate in such a competitive manner.
What if it were able to work in order to reward helpful and selfless behaviors?
In nature, there are many examples of animals helping each other to survive and reproduce,
even at the cost of their own welfare.
Such behavior is called altruism, though many scientists debate if true altruism can even exist.
But examples of this behavior are clearly visible across the animal kingdom.
How do these behaviors come about?
One graduate student in evolutionary biology, William Hamilton, proposed that helpful behaviors
can evolve if they are directed towards kin, or family members with shared genes.
Altruistic behaviors can arise through a process called kin selection, where individuals help
their kin to survive and reproduce at the cost of their own survival and reproduction.
By helping out a relative, the altruistic individual ensures that some part of their
genetic material is passed on to the next generation.
This improves what is called the inclusive fitness of the group, or the increased reproductive
success of the extended family.
This helps compensate for the altruistic sacrifice, or evolutionary cost, of the individual, who
may hinder or even give up their own ability to reproduce, for the benefit of the whole group.
To see such an example of this phenomenon, look no further than an ant mound.
In ant colonies, the only individual reproducing is the queen ant.
All the female ants are sisters, sharing 75% of their DNA because of a haplo-diploid pattern
of inheritance, which we touched upon in a previous tutorial.
Males are haploid, meaning they have only one set of chromsomes.
This is because they inherit one copy of each chromosome from their mother, and they have
no father.
Females are diploid, meaning they have two sets of chromosomes.
This is because they inherit a copy of each chromosome from both their mother and their father.
Since their mothers are also diploid, females inherit one of two possible sets of genes
that come from the mother, and they also inherit the only set of genes from the father, so
this explains the average genetic similarity of 75% among ant sisters.
They will share much less genetic similarity with their sons, given that the males have
half the genetic material.
Because of this, females are more related to their sisters than their own offspring.
Many ants will spend their whole lives only to die in foraging and protecting the nest,
so that the queen and her offspring, their sisters, may live.
In this scenario, the benefit towards reproductive success of the queen would have to outweigh
the reproductive cost to individual ants.
Hamilton proposed a rule that stipulates under what conditions altruistic behavior would evolve.
According to Hamilton’s Rule, the altruistic cost of not reproducing is outweighed by the
benefit towards the inclusive fitness of the group.
This idea can be illustrated mathematically by the equation: b>c/r, where b is the benefit
given to others, either aiding in increased survival or reproductive success, c is the
cost incurred by the altruist, such as losing the ability to reproduce, and r is the coefficient
of the relationship, or how closely related the individuals are.
The closer the blood ties, the higher the relationship coefficient.
Here’s an example.
Say that there is a gene that results in an altruistic behavior, such as sharing food
with other members of the group when food is scarce.
If food is shared with members of the group who are closely related, then the r coefficient
would be high.
The cost of losing food would be minimized by the benefit of survival of the close family
members.
If the close family members also carry this gene, then their offspring will likely inherit
this behavior.
In this way, altruistic behaviors can be selected for and increase over time.
Kin selection can lead to the evolution of some unique family structures.
Some experts believe that this contributes to a theory on the evolution of aging.
As individuals age and begin to stop reproducing, they can invest their efforts in their grandchildren
and other relatives.
This increases their overall inclusive fitness, so extension of life after reproduction to
care for relatives would be selected for via kin selection.
This explanation as to why life is extended after reproduction, particularly for females
so that they can care for grand-offspring, is known as the grandmother hypothesis.
Kin selection can also be taken to the extreme.
In some cooperatively breeding species, especially birds, offspring can sometimes be recruited
as “helpers” to assist in taking care of their siblings.
Occasionally, this can come at their own expense, hampering their own ability to reproduce.
If helpers contribute to the reproductive success of their siblings, breeders are more
likely to prevent the helpers from mating.
This parent-offspring conflict can evolve, where fathers typically disrupt the mating
activities of their sons.
So that’s a bit about kin selection, which is a side of natural selection we don’t
typically think about, given that it is the precise opposite of the cutthroat competitiveness
we are used to discussing.
But given the success of certain altruistic species, it is clear that nature has found
an effective strategy.