There’s a thesis that when you look at an embryo, it passes through the prior evolutionary steps before it arrives at “the present”. So we have a stage that looks like a fish embryo, and one that looks like a reptile, etc.
This is captured in the phrase
‘Ontogeny recapitulates phylogeny’
This famous proposition from biology suggests that, if we have similar embryologic development, we are closely related.
The idea goes as follows. Embryogenesis is a developmental sequence at the earliest parts of life for a multicellular organism, an early way of structuring a mass of dividing cells into a body plan.
There is a sequence of operations in early development that specify important changes that later stages all build upon. Those later stages depend upon prior stages to have been established before they act. Natural selection might intervene here or there in that sequence, but it can make a far more reliable and survivable impact later in a developmental sequence, because it doesn’t interfere with all of the previous development. Earlier stages in development for related species of organisms must thus be more conserved, an idea that tends to bear out within members of close taxonomic groups.
Taxonomies, when they are well-grounded, group organisms in hierarchies based on shared characteristics. Add notions of ‘family trees’, and you get ‘phylogeny’. The basic urge of phylogeny is to understand common derivation. Convergent evolution of characteristics can complicate this analysis, but new genetic and developmental analyses have resolved a number of these confusions.
From this point of view, we know for sure that humans evolved from primordial fish and other earlier vertebrates. Human embryos first develop gill slits and a tail, both of which are usually resorbed as unnecessary when later human developmental programs kick in, all in utero. For a time, our embryos are also anatomically difficult to discriminate from a chicken embryo (and class Aves in general), or from a turtle embryo (order Chelonia), the latter a vertebrate derived very early on from other reptiles, apparently prior to the dinosaurs.
You are more like a turtle than you might realize.
This is a rather true proposition.
What I’m postulating, is that the trend continues to some extent during development into an adult species.
We’re all familiar with someone calling The Kids “Yard Apes”, and as a child I loved nothing quite so much as climbing in trees and eating fruit found there…
In my front yard is a “Tangelo” Tree. This is a citrus made by crossing a Grapefruit with a Tangerine. I harvested these fruit in the fully mature stage, with sweet eating out of hand and a “top knot” similar to some tangerines, for several years before I discovered an interesting thing about them.
Like many epiphany moments, this was fueled by Tequila. But not in the consumption, but in the desire for consumption… You see, I found that I had NO lemons nor limes. But I did have a citrus tree in the yard with immature fruit on it.
The citrus in question is a Dancy Tangelo, also known as the Minneola Tangelo.
Larry K. Jackson and Stephen H. Futch
The Minneola tangelo (Figure 1) is a Duncan grapefruit x Dancy tangerine hybrid released in 1931 by the United States Department of Agriculture Horticultural Research Station in Orlando. This tangelo (like other tangelo cultivars) is therefore 1/2 tangerine and 1/2 grapefruit. The fruit is quite handsome and a genuine pleasure to eat.
I’ll second the notion that it is a genuine pleasure to eat. Like a Giant Tangerine but more interesting at full maturity. But this posting isn’t about eating mature Tangelos. Nope, not at all… You see, I had Tequila and needed sharp sour citrus… A mature Tangelo is very sweet, not sharp or sour at all.
So I did what any Red Blooded Celtic German English American would do, I went out and looked at my tree and said “I do ne care if ye be ne ripe, I’m gonna pluck yew, and cut yew, and suck yer juices dry!” and picked the thing on the tree that looked most like a lemon. Smaller than full grown and not at all “ripe”. But 3 shots into it, wanting a 4th, “ripe” is not a barrier…
Imagine my surprise when not only was this an “adequate” substitute for a shot to a 3 times abused tongue, but was rather nice!
Well I’ll spare you the long and slow details. Just let’s agree that over the next few months (no, not Tequila Months… that was over and done in just a day … or maybe two… it’s a bit fuzzy… but actual months): I tried the little yellow ones when I needed a lemon, and the green ones when I needed a lime, and the bigger orange ones (but missing their “top knot”) when I wanted more of an orange effect. They ALL were FINE for the expected role.
Well, not quite all. VERY small green ones were a bit too dry to stand in for limes. Let ’em get to Lime Sized and it’s fine.
So now I look on my Citrus Tree, and realize I’m very much going to miss it as we re-candle to Florida. It has given me lime, lemon, orange, and Tangerine-On-Steroids fruit for neigh on 35 years now. Far more useful than any other thing I’ve planted and grown over the years. Dozens (hundreds?) of chickens with “citrus marinade” of various types, all from the same tree. More bottles of Tequila “rescued” by a “reach and grab” than I can count.
But I find myself wondering: Does this tree say something more? Does it explain why a 5 year old me loved climbing fruit trees and “hooting at the world” as a howler monkey might, but a 60+ year old me does not? Does it explain why a single tree can provide limes, lemons, oranges, and Tangelos? Do “we”, species writ large, recapitulate phylogeny in our development, even into our old age and into our graves?
Are some of us “fully mature” as 12 year olds (cough cough… at least mentally) while others are not emotionally mature into their 20s? (cough cough again… Speculating that analytical maturity can arrive decades before emotional maturity and “that’s a geek”…) simply because some “gene cascade development sequences” take more time than others? Is it perhaps down to methylation and sequencing even into old age?
My Citrus Tree has taught me more than one might expect. It has shown to me how evolutionary genetics is more important than total gene inventory. It has shown me that “what I EXPECT is not as important as WHAT IS”. It has shown me that the one thing I thought it could do was far far less than the total inventory of what it could offer. It has taught me that “methylation” and variable gene expression over time really really matters.
It has also taught me that just as “desperation is the mother of invention”… Tequila needs can drive discovery and creation.
This posting was brought to you by the early stages of “Tequila Appreciation”. No more than 6 shots were involved in the creation of this insight. Also, only ONE Orange State Tangelo was involved, cut into no more than 8 segments. (two yet to go..)
I have a Green Lime Stage Tangelo “on deck”, so do not be surprised if it is “All Down Hill from here”, and any comment made more than 4 hours (or 8 shots) from now is disavowed as the product of Chemical Coercion. After all, Chemistry is “White Supremacist Racism” so it can’t at all be my fault if it influences me a bit too much “going forward” ;-0