Even though we've had many conversations with the sprogs on the general topic of evolution, the influence of pop culture (and especially cartoons) seems sometimes to muddle their grasp on the details. Last night, we revisited the subject.
Dr. Free-Ride: You wanted to talk about evolution.
Younger offspring: Mmm-hmm.
Dr. Free-Ride: What about evolution did you want to talk about?
Younger offspring: What evolved into humans?
Dr. Free-Ride: And at the dinner table, how did you phrase the question?
Younger offspring: At the dinner table, I think I said, "What creature was in between the ape and the human?"
Dr. Free-Ride: And [Dr. Free-Ride's better half] suggested that that wasn't the right way to look at it. Can you explain what the problem is with imagining that apes evolved into humans?
Younger offspring: Well, the problem with that is that apes are still alive now, humans are still alive now, they were evolving in the same period of time. So how could one ape evolve into a human? It's like [elder offspring] evolving into me.
Dr. Free-Ride: Which strikes you both as ridiculous.
Elder offspring: Yeah, there's no way [younger offspring] is related to me.
Dr. Free-Ride: Um, no. You're related. Deal with it. Anyway, I guess the best way to think about where humans came from and where apes came from is that we have some common ancestor -- kind of like your grandparents are ancestors you share with your cousins.
Elder offspring: We're related to our cousins, but not exactly alike.
Dr. Free-Ride: But you are in the same species, which means potentially that human cousins could have offspring together. Anyway, we're talking about many, many more generations between humans, and apes, and the common ancestors we share.
Elder offspring: Lots of generations.
Dr. Free-Ride: Anyway, knowing what you do about humans and apes, what do you think our common ancestor might have been like?
Younger offspring: Our common ancestor might have been like ... yeah, I've got nothing. I think I'll draw it.
Dr. Free-Ride: OK. And do you have any thoughts on what our common ancestor with apes might have been like?
Elder offspring: Trilobites.
Dr. Free-Ride: What?!
Elder offspring: That's a very, very, very, very, very, very, very early common ancestor.
Dr. Free-Ride: Really? Of us and apes?
Elder offspring: Well, I think we're distantly related.
Dr. Free-Ride: Very distantly. Well, it's hard to roll the tape back to see where all the creatures that are here today came from -- since the common ancestors different kinds of organisms share aren't around now, it can be hard to imagine what they were like. I wonder if you have any ideas on how, from our common ancestor, we ended up with humans and apes (and possibly other relatives) the way they are now. How did the descendants of this common ancestor get to be different?
Elder offspring: Well, how evolution works is parents have offspring that are slightly different from the parents, and then they have offspring and their offspring are slightly different from them, and it keeps going on and on and on until you get the final product.
Dr. Free-Ride: But what makes those differences between generations?
Elder offspring: Mutation.
Younger offspring: Well, I think, over the years, those ancestors decided to change their way. They decided to live a better life. So, they went to cavemen, who had clothes -- not regular clothes from the modern time, but clothes -- and they had all these clubs, and they slept on rocks, and they lived in caves.
Dr. Free-Ride: That's an interesting idea. So, you think it was based on decisions by the common ancestors and their offspring about how to be. And you over there, you're just talking about random changes in the heritable traits from one generation to the next.
Elder offspring: Yes. And adaptations to help them survive in their environment.
Dr. Free-Ride: Ah, adaptations! That's very important. Do you remember the force that Darwin thought was very important in evolution?
Elder offspring: Natural selection?
Dr. Free-Ride: Yeah, so do you know what natural selection is?
Elder offspring: The ones who survive go on to have offspring, the ones who don't, don't.
Dr. Free-Ride: But what makes a difference in which organisms survive long enough to have offspring and which don't?
Elder offspring: Those that survive long enough to have offspring will have more of their type of creature.
Younger offspring: But why do those ones survive and the other ones don't?
Dr. Free-Ride: The idea is that the traits you have can be inherited through your genes. If some of the characteristics you have are really well suited to your environment --
Elder offspring: Then you survive and breed.
Dr. Free-Ride: At least, you have a better chance of surviving. There's still some luck involved.
Elder offspring: And then at least some of your offspring survive and breed, and then at least some of those survive and breed, and it goes on and on and on.
Dr. Free-Ride: Sure. But what's happening there is that some of the traits that really don't work so well in that environment, if the environment in relatively stable, just won't last very long because the creatures that have those traits won't last long enough to breed and pass them on to offspring. So here's a thought: If there are apes and there are humans, and they have a common ancestor, maybe some of the common ancestor-type creatures, whatever they were, were in one kind of environment where the traits we'd think of as ape-like traits helped them to survive better, and maybe some other of the very same common ancestor-type creatures were in another environment where what we think of as the human traits were the ones that were useful for staying alive long enough to have offspring. Or, possibly, they could have been in very similar environments and ended up with two different ways to do well in that environment.
Younger offspring: Apes wear hair, we wear clothes.
Elder offspring: And we cook.
Younger offspring: And apes dig food out of each other's hair.
Dr. Free-Ride: After a certain point, maybe we ended up with adaptation that were different from the ones our cousins the apes ended up with.
Younger offspring: My brother the ape!
Dr. Free-Ride: The song may say "my brother," but I'm inclined to think the relationship is more like cousins than siblings.
Elder offspring: It's more of a brother than the shrimp.
Dr. Free-Ride: Sure, and the shrimp is in the song too, I understand.
Younger offspring: And the lichens!
Elder offspring: And the anteater!
Dr. Free-Ride: But I'm not sure how you'll feel about this part: I don't think necessarily that the changes between us and the apes were anything that our ancestors intended. I think some of it was just whether the traits they had helped them survive in the environment they had, so they could have babies with the traits that they did. And some of it was luck.
The sprogs then went off to draw some common ancestors, as they imagine them.
From the younger offspring, a common ancestor of modern humans and modern apes (who also appears to be an ancestor of modern blue meanies:
From the elder offspring, a transitional form between trilobites and monkeys:
I wouldn't have even thought to look for such a transitional form. Shows what I know.