Imagine meeting someone and instantly knowing you’d do anything for them. That’s how I felt when I first saw my son, Harrison. But why do we feel such strong connections to our children? The answer lies in evolution.
Evolution is all about survival and passing on traits to the next generation. Traits that help an organism survive and reproduce become more common over time. This is called natural selection. The success of a trait in being passed on is known as its “fitness.”
Our traits, from physical features to behaviors, are influenced by thousands of genes interacting with each other and the environment. Essentially, we are “survival machines” designed to pass our genes to the next generation.
Altruism is when you help someone else, even if it costs you something. But why would evolution favor such behavior? If I risk my life for my son, I’m ensuring that at least some of my genes continue to the next generation.
Biologist W.D. Hamilton created an equation to explain this: if the cost to you is less than the benefit to the other person, multiplied by how closely related you are, then it’s worth it. This is called “kin selection.”
Let’s say a dangerous situation arises, and I have to choose between saving my brother or my son. Both share 50% of my genes, but my son has more “reproductive potential” because he’s younger and likely to have more children. This means saving him could ensure more of my genes are passed on in the future.
Animals also show altruistic behaviors. Meerkats keep watch for predators, vampire bats share food, and scrub jays help raise siblings. These actions make sense if the animals are related, as they help their genes survive through their relatives.
While we don’t consciously calculate genetic benefits, evolution has shaped our behaviors. Helping family members ensures that part of us continues into future generations. Love and kindness, influenced by evolution, play a crucial role in our survival.
So, why do we care so deeply for our family? It’s partly due to evolution. And remember, you can’t spell evolution without love!
Thanks to 23andMe for supporting this exploration of evolution. 23andMe is a company that helps people understand their DNA, which is organized into 23 pairs of chromosomes. They offer a special holiday deal if you’re interested in a science-themed gift for your family.
Stay curious and keep exploring the wonders of science!
Explore your surroundings and identify traits in plants, animals, or even humans that might have evolved for survival. Take notes or pictures and explain how these traits could have been influenced by natural selection. Share your findings with the class.
In groups, create a short skit demonstrating a scenario where kin selection might occur. Consider situations where family members help each other, and explain the evolutionary benefits of these actions. Perform your skit for the class and discuss the concept of altruism.
Research your family tree and identify traits that have been passed down through generations. Create a visual presentation or poster showing these traits and discuss how they might have contributed to your family’s survival and reproduction.
Participate in a debate about whether altruism is more prevalent in humans or animals. Use examples from the article and additional research to support your arguments. Consider the role of kin selection and reproductive potential in your discussion.
Conduct a workshop where you explore the basics of DNA and genetics. Use online tools or kits to learn about your own genetic makeup. Discuss how understanding DNA can provide insights into evolutionary traits and family connections.
Sure! Here’s a sanitized version of the transcript:
—
[MUSIC] Thank you to 23andMe for supporting PBS Digital Studios. This is Harrison. Harrison’s favorite hobbies include playing, exploring, and keeping me on my toes. Not exactly the number one qualities you go looking for in a friend. Yet, I knew he was the world’s most perfect human the instant I laid eyes on him. I knew I’d give up everything I have for him, even my life, without hesitation. All of that, even though just a few months ago, we’d never even met. The reason why? Evolution, of course.
[MUSIC] Staying alive long enough to have healthy offspring and passing our traits from one generation to the next is how we succeed in the big-picture game of evolution. It’s kind of the whole point. Some traits, whether it’s being tall, having stripes, or unique features, help us succeed more than others. If they increase an organism’s chances of surviving and reproducing, then they’ll become more common in the future. This is one of the basic principles in the theory of natural selection.
The measure of how successful a trait is at making it to the next generation is called fitness. A trait that’s more likely to be passed on has higher fitness compared to one that’s less likely to be passed on. What we know today, and what Darwin didn’t know back when he was figuring all this out, is that all these traits—from how our bodies are built to how we think—are the product of thousands of genes, all interacting with each other and the environment. Knowing that makes you realize we are survival machines. We exist to get our genes into the next generation. Congrats! Now you know the meaning of life.
Harrison represents my genes in the next generation. Well, half of them, anyway. He’s my son. Did I not mention that before? What did you think, that I just found someone’s baby? Now, just for fun, let’s say a pack of velociraptors tries to snatch him away. But I step in and sacrifice my life to save his! Which I would totally do. Because he’s awesome.
This self-sacrifice is an extreme example of altruism, which basically means your pain for someone else’s gain. The thing is, this kind of risk or ultimate sacrifice doesn’t immediately make sense when you think of evolution. If I become velociraptor food, my future chances of reproducing are now zero. Because I’m gone. So why would I give up 100% of my genes, the ones in my body, to save just half of them, the ones he carries? It might seem like a really bad exchange on my part, but it actually makes sense.
And some pretty basic math can help explain why. Whether an act of altruism is worth it depends on the relationship between the two parties involved. The biologist WD Hamilton actually came up with an equation for this: It factors in the cost to you, C; the benefit to the other individual, B; and how closely related the two of you are, r. Let’s unpack this equation a bit. If the cost to you is less than the benefit gained by the other individual, multiplied by that individual’s relatedness to you, then acting altruistically is worth it in the eyes of evolution.
When two individuals aren’t related at all, r will be zero. Let’s say a bus full of velociraptors is careening towards a stranger, completely unrelated to me. If I push them out of the way and die myself, I completely lose while the stranger completely wins. They might print something heroic about me in the newspaper, but technically this is not the kind of behavior that evolution rewards. But if the relatedness is greater than 0, things work differently.
Let’s say the raptor bus is careening towards my first cousin, and I die saving them. Because my cousin and I have one-eighth of our genes in common—our r is 0.125. In this case, I don’t completely lose. I only lose a portion. If I push my sister out of the way of the raptor express? Well, my sister and I have one-half the same genes, so I only lose half.
Understanding this, biologist JBS Haldane reportedly said that he was “prepared to lay down his life for eight cousins or two brothers.” But let’s say I’m given an even more difficult choice. Two buses of velociraptors, one heading towards my brother and the other my child. My brother and Harrison both share 50% of my genes. I’d lose either way! How do I decide what to do?
Well, I really hope I never actually have to make this choice, because I love my brother too, but I suspect most parents would save their kid first, and evolution has a good reason for that. Because Harrison is a tiny baby with his whole life ahead of him, he has the greatest “reproductive potential” among us. That’s a fancy way of saying that Harrison is likely to have more children from this point on than either my brother or I will.
This is where we see the influence of genes through generations. Each one of Harrison’s future offspring will share about 25% of my genes. If he has just two kids, I break even on my sacrifice. And if he has more than that, or if any of his kids have kids of their own, I’d actually be ahead. All of these potential grandchildren and great-grandchildren mean sacrificing myself for my child is a better decision for the future of my genes than by letting my child die.
Now we’ve been focusing on the most extreme examples of altruism, giving up your life, but the fact is altruistic acts are fairly common among social animals. Meerkat “guards” keep watch over the colony and raise an alarm if they spot a predator, which puts them at risk. Vampire bats share food with neighbors that don’t get enough, and scrub jay chicks hang around the nest after they grow up and help their parents raise their siblings.
If the individuals in these groups were completely unrelated, it’d be difficult to explain why they do this. But! If the group members are related to each other, even only distantly, genes that underlie altruistic behaviors like caring for children, protecting members of their group, and sharing food might spread through a population not by increasing an individual’s own survival, but by helping an individual’s genes survive in their relatives—a mechanism known as kin selection.
Kin selection can help us to understand how complex human behaviors might have evolved. Of course, none of us sit there and run equations in our head to decide if it’s worth helping the people we care about. And we can’t trace an emotion as complex as love or kindness directly to a gene or two. But the way humans behave has been influenced by evolution the same as any other animal. Helping each other helps us survive, and not just in this generation. It ensures some part of us will make it into the next, and the next, and the next.
So, why do we care for our family? Why would I, or any other parent, sacrifice everything for our children? It’s evolution. I mean, at least in part. And you can’t spell evolution without love, right? Stay curious.
A big thanks to 23andMe for supporting PBS Digital Studios and our show. 23andMe comes from the fact that human DNA is organized into 23 pairs of chromosomes. 23andMe is a personal genetic analysis company that was created to help people understand their DNA. If you and your family each get your 23andMe results, you can unwrap how much Neanderthal DNA you each have.
23andMe has a special holiday offer now through December 26, in case you’re looking for a science-themed gift. You can go to 23andMe.com to check out their holiday offer and get kits for your family. Show your support for this show by checking out 23andMe.com/OKAY.
A big thank you to our special guest Harrison. You guys like his shirt? Let me know in the comments. Maybe we’ve got another merch idea. How’d you enjoy your YouTube debut? Was it fun? Leave him a nice comment, and I’ll read them to him right before he goes to sleep. Thanks for joining us, we’ll see you next time. Stay curious!
—
Let me know if you need any further modifications!
Evolution – The process by which different kinds of living organisms develop and diversify from earlier forms during the history of the earth. – Charles Darwin’s theory of evolution explains how species adapt over time through natural selection.
Altruism – Behavior by an individual that increases the fitness of another individual while decreasing the fitness of the actor. – In biology, altruism can be seen when a worker bee sacrifices itself to protect the hive.
Survival – The ability of an organism to continue living and reproducing in its environment. – The survival of a species often depends on its ability to adapt to changing environmental conditions.
Traits – Characteristics or features of an organism that are inherited from its parents. – Eye color and leaf shape are examples of traits that can be passed down from one generation to the next.
Natural Selection – The process where organisms better adapted to their environment tend to survive and produce more offspring. – Natural selection is a key mechanism of evolution, as it leads to the development of advantageous traits in a population.
Fitness – The ability of an organism to survive and reproduce in its environment. – In biology, fitness is often measured by the number of offspring an organism leaves in the next generation.
Kin Selection – A form of natural selection that favors altruistic behavior toward close relatives, resulting in the increased survival of shared genes. – Kin selection explains why animals might help their relatives raise offspring, even at a cost to their own survival.
Genes – Units of heredity that are transferred from a parent to offspring and determine some characteristics of the offspring. – Genes carry the instructions for building proteins, which are essential for the structure and function of cells.
Family – A group of related organisms that share a common ancestor and often exhibit similar traits. – In biology, a family can refer to a taxonomic rank used to classify a group of related species.
Behaviors – The actions or reactions of an organism in response to external or internal stimuli. – Animal behaviors, such as migration and mating rituals, are often studied to understand how species interact with their environment.
