Part IV of SHHML takes us away from traditional methods of heritability into the weird world of DNA-less information transmission. "You, My Friend Are a Wonderland" starts off with a fascinating tale of a glowing fish that doesn’t actually glow. It turns out this clever fish has formed a mutually beneficial relationship with a special glowing bacteria that has infected each newly hatched fish for thousands (at least) of generations. Zimmer points out this phenomenon can be found throughout the animal kingdom from fish, clams, and all the way to our own cells. Bacteria have altered their own DNA to adapt to the perfect host and in doing so they ensure their transmission from one generation to the next.
One of the most amazing examples of this cross species heritability has become such an important part of our existence that it seems incorrect to consider them a separate species. Mitochondria have been carrying their own DNA through generations of our cells ensuring their survival by passing through maternal germlines into offspring. Until the 1980’s the majority of scientists considered this too outrageous an idea to consider it as an answer for some of the most baffling genetic disorders.
In the next chapter, "Flowering Monsters," Zimmer outlines to history of epigenetic discoveries. Epigenetics is a process of altering an organism through the expression of their genome, rather than the actual genome. In the 1700’s when naturalist, Carl Linnaeus, learned of a shocking flower capable of detouring from its original species into something else completely, he was chastised for such blasphemous ideas. It wasn’t until almost 300 years later, that scientists discovered the L-CYC gene in Linnaeus’s monstrous flower, Peloria. It turned out that this gene was not mutated in the species, but rather silenced. Genetically speaking, Peloria is identical to its toadflax relatives but the new flower differed in how it expressed its genes. It turns out, this process is quite common in plants as they respond to their environment by altering their gene expression and passing this altered gene expression down through their offspring, but here is where things get really weird.
Mammals also appear to alter their gene expression in response to their environment and even more remarkably, this altered gene expression seems to be passed down through generations. Here’s the catch, how is this possible if all mammalian germ cells are set aside early in embryo development? If our sperm and eggs are already programmed with our genetic material and set aside until fertilization, how can environmental impacts throughout our lives make their way into the next generation? This isn’t a problem for plants don’t set germ cells during early development, they produce them years down the road when they are ready to reproduce.
Despite all of the biological obstacles in the field of mammalian epigenetics, researchers have found multiple instances of acquired, and then inherited, behavioral responses to specific environmental stimuli. The field is still new, and researchers are working hard to understand how environmentally altered gene expression makes its way into the next generation.
In the final chapter of Pt. IV, "The Teachable Ape," Zimmer examines cultural transmission of knowledge. It turns out, not all important information is transmitted through biology, some things have to be learned. Chimpanzees learn to make tools, birds learn how to open a milk containers, and bees learn how to access an inaccessible flower, all through social observation. These learned behaviors are not instincts born into the next generation, but rather learned from one generation to the next.
Zimmer expands on cultural transmission in humans, pointing out that we not only learn through observation, but we seem to be biologically predisposed to teach and learn from each other in ways that other animals are not. For example, human children will imitate a teacher with blind faith rather than solving a puzzle through their own devices like a chimpanzee will. Zimmer points to this ability to imitate as a special ability to learn from others. He also points out that humans are much more prone to demonstrating behaviors for each other than other animals are and he considers this as one explanation for why humans have been able to alter the environment around them in ways that other animals have not.
Most interesting parts of the reading:
Microbiome: Us as individuals but also with our gut microbiome
- Kids teaching each other
- Friendliness of humans to each other
- Youtube culture, how humans are learning from each other is changing with technology
- Imagining bee experiment
The number of lactose intolerant people much higher than expected
- Historical examples of heritable culture not being respected
- Parents stress being passed to offspring
- Zimmer didn’t cover epigenetics much in depth, maybe because research is so new
- No clear explanation of the basics of epigenetic modifications
The effects of parenting on offspring
- Parenting is really difficult and there are societal/cultural pressures that shape parenting as well
- Partner choice is different at difference points in your development
Does heritability encompass more than genetics? How strong was Zimmer’s argument in favor of heritability being broader?
Andi DeRogatis is a graduate student at UC Davis in the animal biology graduate group. She is currently studying how the avian immune system is influenced by the process of molt. She loves all things birds and is passionate about getting others excited about birds as well! Her email is firstname.lastname@example.org and you can follow her on Twitter @andiderogatis.
Logan Savidge is a graduate student in the biological psychology program at UC Davis. She works with titi monkeys in Karen Bales’ lab to study the biology and neuroscience of parent-child or adult partner attachments. She is also currently working as the public information officer for the California National Primate Research Center (CNPRC). She manages their social media platforms and provides content for the website. Follow her and the CNPRC on Twitter @Loganesav @CNPRCresearch.