| Happy new year! A time to reflect, look back on the past, and focus on change. A biodiversity lover such as yourself intimately understands what change means in the natural world. |
| When we focus on evolutionary questions, that change is measured in many ways. For example, The amount of gene flow between populations, the degree of divergence between 2 subspecies, or the change in gene frequencies over time in isolated populations. However, the fundamental unit of “change” in evolution, is mutation. |
| The incredible diversity of life we see today is due to nearly random mutations that are then selected, exchanged, and stochastically sorted into the numerous organisms we share this planet with! |
| Yet, mutation is usually considered the weakest of the 4 primary evolutionary forces (The others being, drift, gene flow, and natural selection). |
| This study found the average mutation rate for humans is ~1.24×10^-8 mutations per base pair per generation. The genetic dataset they used was 2.7 Gb of our genome, Gb being Giga- base pairs, Meaning, of the 2.7 billion base pairs, only ~33 mutations would occur between generations on average. |
| Then lets not forget our types of mutations! Silent mutations (synonymous) account for roughly 20% of all mutations. These mutations create the same amino acid as their un-mutated form, lowering the potential impact of novel mutations even more. |
| Additionally, where on the genome this mutation occurs matters! Over 90% of our genome is “non-functional”. A mutation in these non-functional regions will have little to no impact on our biology. These neutral mutations will then evolve almost exclusively under the forces of genetic drift. |
| We then see that the diversity of life is initially created by mutation, however most mutations are inconsequential. It is the other forces of drift, selection, and flow that largely drive the wedges between biological groups. Creating the branching pattern we see across the tree of life. |
| But as any good biologist knows, it depends. |
| While there is no doubt forces like natural selection can result in drastic evolutionary changes, mutation is not always so meek. For instance, we only need to look at polyploid organisms to find evidence for the power of mutation. Polyploidy, the condition of having more than 2 sets of chromosomes, can arise as an extreme case of mutation often through abnormal cell division, hybridization, or fertilization from more than 1 male gamete. |
| While relatively rare in vertebrates, polyploidy is quite common in plants. In fact, the entire human agricultural system relies on polyploidy to produce new varieties of crops extremely quickly! While this synthetic polyploid evolution occurs much more frequently than in natural populations. |
| Most new mutations in a population are often removed by natural selection, lost by genetic drift, or swamped out by gene flow. The mutations that do persist, may need many generations and millions of years to diverge into new species. However, polyploidy can result in instant speciation between generations. After all, the doubling of a genome represents a significant difference from the previous generation! |
| Naturally, there are more nuances, caveats, examples, and “it depends”-isms surrounding polyploidy any mutations. However, these topics are my favorites to explore! |
| Evolutionary forces courses? |
| Each layer of we peel back reveals another piece of the evolutionary story that connects all of us. To peel back the curtain a bit, my next major course offering will be on the primary evolutionary forces. Throughout my career as a biologist and as an nature educator, I see repeated misunderstanding for how evolution operates. For example, the overemphasis of natural selection as an evolutionary force. Further, I find many of my students only have a vague idea for how these forces work or are mostly unaware for population size changes the dynamics of each. |
| I certainly struggled when I first started. Growing up in Texas, my first evolution course that even mentioned genetic drift wasn’t until my senior year of college. Its what inspired me to go into Evolutionary Biology for grad school and these topics are now my favorite to teach! In the next email, I’ll be covering genetic drift. Perhaps my favorite of the forces! If you have something you’d like covered in one of the newsletters, feel free to let me know! |