One billion years ago, iron oxides, microbes, and a reflected noxious sky, color the coastal water red & blue. In these quiet tidal pools, among the bulbous stromatlites, colonies of differentiated cells smaller than a grain of sand, the ancestors of all metazoans, may already be stirring. This image was provided by graphic artist Karen Wehrstein on super-short notice, exclusively for this post (Enlarge)
Some zipped around like tiny jet aircraft, powered through the viscous media by rows of cilia or a single whip-like flagella. Others lazily poured themselves into one advancing pseudopodia after another, moving and engulfing their prey like the blob. A few found safety in numbers and grouped in bulky mats, preserved to this day as stromatolites. And here and there, perhaps a handful had organized into groups of burgeoning specialized cells--the first metazoans. But there's an even more exciting change in the works and it will become all the rage: We're talking 'bout sex!
The precise details of the origin of sex remain a mystery. Since it probably happened in subtle molecular steps starting a billion or more years ago, stretching across countless generations of microbes and the earliest multi-cellular conglomerates, it may turn out that no detailed discernible record is preserved into our own time. If so, we may never know exactly what events transpired. One guess based on what we can observe now is that some microbes or colonies of microbes evolved a more organized system of swapping out sequences of genetic material, perhaps aided by either domesticated or pathogenic viral elements, and over time, the genetic components and related structures that facilitated this process were slowly crafted through the ages by selection. Eventually, cells became specialized at performing functions we'd now identify as a male or female role. We see evidence of this possibility today: Yeast can reproduce asexually, but some species also have two different versions which differ in a few proteins that act kind of like mating groups. This difference might resemble the ancient genetic forerunners which led, eventually, to the first wee-wees and nu-nus.
How ever it happened, sex was a significant change (And who wouldn't argue a delightful one?) in the reproductive process, and evolution seems to have taken off like a rocket--no pun intended--as sexual reproduction became commonplace. Are the two connected? That question is a real hot potato.
One line of thought is that prior to sex, variability was limited, because the entire parent genome was replicated intact. Using that method, the only way a useful gene could become widespread in a population was for all the competing lineage's to die off. The offspring were thus almost identical to the parent. Mutations, both good and bad, were preserved. After sex arose, genes could flow horizontally through the entire population and become fixed or removed quickly based on the value they conferred. A related idea is that forming one entirely new, healthy individual by recombining two existing ones, was a source of constant variety for selection to work on. But it should be emphasized that there is a lot of debate among evolutionary biologists regarding the adaptive value of sexual reproduction.
This diagram illustrates how sex might create novel genotypes more rapidly. Two advantageous alleles A and B occur at random. The two alleles are recombined rapidly in (a), a sexual population, but in (b), an asexual population, the two alleles must independently arise. (Illustration courtesy of the Wikipedia)
Fast forward a billion years and sexual species make up a huge portion of the familiar biological world that we call home. True, much of the modern environmental infrastructure developed and still rests on a foundation of asexual bacteria and archaea, and of course without microbes there would be no beer--egad! But the crops we harvest, the meat we consume, the plants we use for decoration, the trees-tops our primate ancestors evolved in; almost all of it is composed of sexually reproducing species. But sex created something else. Before sexual reproduction, all creatures were, for lack of a better term, mothers, and all descendants were daughters. But afterward, a new element came into the picture: Dads.
Moms may have had a three-billion year headstart on fathers, but fathers have certainly made up for lost time. On earth today, they may be found clothed in chitin, scales, feathers, or fur. They can be deadly to outsiders while doting to their children. Males of every species are spread across the world and throughout the animal kingdom, from tending eggs in the Antarctic to presiding over clans in the rainforest.
In our socially complex human species, a biological father and a Dad play two very different roles in child rearing. In the modern family, a Dad can be anyone who steps up and helps raise us; a stepfather, an uncle: anyone who acts as a provider, a mentor, a role model, or protector. I was adopted at birth, I don't know who my biological parents were. But from my first, infant memory, there has never been any doubt about who my Mom and Dad are.
My Dad grew up in the 1930s without a father. He was one of four kids raised by a single mother on a school teacher's depression era salary. When he was just getting old enough to enjoy some independence in an economy that was perking up, a world war engulfed most of the planet. After WW2, he served his country and went on to help create the precursors that led to home computers. He also put up a roof over my head, food on my plate, and spending money in my pocket; all while putting up with more headaches and mischief from me than anyone should ever have to endure. Through it all he was gentle and modest, he raised me with love and instilled in me a fondness for books, only two wonderful gifts out of so many he provided. He is my hero, my champion. I bet we have some sons and daughters here today that feel the same way about the father figure in their lives, so please, tell us about them if you wish.
One day is hardly enough to recognize a billion years of evolution or commemorate a lifetime of love. But for what it's worth, from all the sons and daughters in the Daily Kos community to you: Happy Fathers Day!