miRNAs are short RNA molecules that do not code for proteins, but instead regulate gene expression after transcription. They bind to messenger RNA molecules and either block them from being translated or mark them for destruction. While microRNAs do not change the DNA or chromatin directly, they are often included as part of the broader category of epigenetic regulation because they affect gene expression without changing the genetic code.

Mammals undergo a somewhat unique type of epigenetics known as genomic imprinting. In this, imprinting occurs in the germ-line - meaning the cell with the silenced genes will be the sperm/egg. Heavy methylation results in the silencing of genes in offspring and can result in sexual conflict between males and females of the species.

Using lions as our example - the male lion "wants" his kids to be as big and strong as possible, and he mates with multiple different females. The female doesn't want this, as it will require more energy and more inherent risk from her. As such, genes are imprinted by the parents so that mom is passing on silenced growth genes, while dad is passing on active growth genes. This balances out and we get a normal sized lion. But if a male lion breeds with a female tiger - who does not imprint this particular gene - the liger ends up larger than either parent.

Epigenetic changes are influenced not only by the internal needs of a cell but also by external environmental factors. These factors include stress, diet, exposure to toxins, physical activity, and even social conditions. 

One area that has been widely studied is the effect of chronic stress. In both humans and animals, exposure to long-term or early-life stress has been shown to cause changes in DNA methylation patterns. These changes often affect genes involved in hormone regulation, brain development, and immune response. As a result, individuals exposed to significant stress may show long-term changes in mood, behavior, or physiological responses.

Some epigenetic changes caused by the environment can also be passed to offspring. This is known as transgenerational epigenetic inheritance. In animal studies, for example, mice exposed to stress before reproduction have produced offspring with altered stress responses and changes in gene expression, even when the offspring themselves were raised in typical conditions. This suggests that the environmental experiences of one generation can influence gene regulation in the next.

One of the most well-known human examples of this is the "Dutch Hunger Winter," a famine that took place in the Netherlands during World War II. Children who were in early development during the famine experienced higher rates of obesity, diabetes, and cardiovascular disease later in life. In some cases, similar effects were observed in their children as well. Research has linked these outcomes to changes in DNA methylation patterns.