War of the Sexes : Part 1
Part 1 NUTRITION, SURVIVAL and REPRODUCTION
The first Law of Nature on Earth, is that sufficient numbers of individuals of organisms must survive long enough to reproduce. If not enough survive, if not enough reproduce, the species dies out. Since all living things die, Nature selects for those groups of organisms which have successful ways of not just surviving, but reproducing. The most misquoted, misinterpreted and misunderstood section of Charles Darwin’s discussion of Natural Selection in evolution is “survival of the fittest”. It should more appropriately be read as ‘survival of the fit enough’.
The oldest and simplest form of reproduction is single cell division to form a clone or ‘daughter’ cell. Most single-celled organisms reproduce this way. Prokaryotes are single-cell organisms with no nucleus or other identifiable cellular organelles, and its DNA is diffused throughout the cell. The primordial Earth environment had no protective atmosphere or ozone layer to filter the sun’s radiation. These early single cells of life were prone to UV radiation damage, especially with no protective nuclear membrane for their DNA.
From the earliest beginnings, reproduction has involved exploitation, conflict, and compromise between individuals. All organisms must “eat”, they need to metabolise nutrients to gain the chemical energy needed to push the chemical reactions to grow, replace or repair damaged cell components, and especially to reproduce. Even the simplest cloning cell-division reproduction method, requires doubling of every cellular component, and so, only the largest, healthiest nutrient-rich cells would have energy resources and get a chance to divide and split into two.
They could not have absorbed enough from the primordial chemical soup, especially if damaged. The most likely method to ensure survival, was to “eat” or cannibalise each other. In prokaryote cells, the DNA of a damaged cell being eaten would be absorbed into the ‘eater’ cell, to form raw material or ‘building blocks’ for the cell to repair and replace its own damaged DNA and other cellular furniture. If they absorbed enough other cells, any additional nutrients to basic survival and maintenance could then be stored and used to provide sufficient ‘power’ for the doubling of all their cell furniture, including DNA, and split into two cells.
Those cells able to scavenge well enough amongst the remains of their more damaged neighbours were the ones that survived and reproduced most successfully. Sometimes fragments of the DNA from the eaten cells might be incorporated intact, into the new daughter generation of cells. An early form of promoting genetic variation.
A binary model of reproductive strategies started to evolve in tandem in the earliest life forms, eons before true sexual reproduction appeared. Small cells versus bigger cells. Smaller cells traded off or ‘sacrificed’ size, longevity and nutrient energy needs of maintenance and growth, to be more opportunistic in reproduction, taking in just enough energy to maintain their DNA core, ensuring the insertion of their DNA into the larger, more nutrient rich cells, often dying in the process but ensuring that their genetic material had some chances of living on by being incorporated into the DNA of the larger cells.
The next step was to form eukaryote cells, with a nuclear membrane to provide some protection for the now single-stranded DNA deep inside the cell and separate it from other cell furniture. This allowed a better chance of protection from being completely ‘eaten’ and a chance to replace and repair damage, and also allowing genes to still survive intact, into the next generation, being harder to fragment. However, this larger more complex cell structuring needs more energy to maintain itself, with little left over for the enormous energy requirement of doubling in size and substance to clone a daughter cell. So more energy was being stored for defence and maintenance of its genetic ‘core’ from other predatory cells. The larger cells became more long-lived with a defence capability, but also less fertile, in that they reproduced less often, but more successfully when they did. Some severe human diseases are caused by long-lived, but slow reproducing bacteria, such as those causing leprosy and tuberculosis. They have such efficient tough defence membranes that they are often difficult to treat taking many months or even years of treatment with specialised drugs.
In some single cell bacteria, a form of sexual reproduction has evolved, known as “bacterial conjugation” in which neither cell dies in a ‘mating’. Some cells in a population contain F-factor genes (or Fertility-factor genes), on a separate small strand of DNA close to the cell membrane surface (known as a plasmid), which is separate to its core DNA strand or chromosome. F+ cells are donors of the F-Factor genes, F- cells are recipients of F-factor alien DNA (with subsequent daughter clone cells being F+), F0 can neither donate or receive, and F1 (or F-‘prime’) are F+ donors, that can donate other core genes as well as the F-factors. Bacterial conjugation, or transfer of F-Factors, and other stray genes between cell lines, is one of the most common causes of antibiotic resistance developing in bacteria.
This takes extra time, energy and effort, which is a “cost” or “risk” to the organism, but the reward or return on such “investment” is in more successful reproduction.
The next step is in moving from single-strand DNA organisms to creating diploid organisms, species which have two copies of all the genes required for survival of the organism, in double-stranded helical DNA. These organisms have developed specialised cells that reproduce in the cloning way for organs and tissues. This is still a cloning reproduction, where cells double in size then split off into two identical cells. This is mitosis, how the cells of the body of all organisms divide and grow.
And also specialised cells for reproduction. They form cells known as gametes which are haploid, with single DNA. The cells divide twice without doubling in size, so only one copy of the DNA is stored in the gamete.
In biological jargon, the form of a species which forms specialised cells for the donating of genetic material, is arbitrarily defined as the “male”, and the form which makes specialised cells for the receiving of the donated material, the “female”.
In general, the ‘donor’ or male gamete cell is small, encapsulating only its DNA and barest minimum energy requirements, are short-lived and produced in far greater numbers than the larger, slower nutrient-rich ‘recipient’ or female gamete cell. Many flowering plants for example, produce both male and female gametes, but the male gamete or pollen is smaller and designed for greatest dispersal, and greatest wastage. Nature produces the small, highly compacted containers of ‘donor’ haploid DNA in excess with minimum short-burst of energy for speed-is-of-the-essence, to ensure that a few survive. Most will not. The majority will not locate a suitable female gamete cell, or even if they do, will fail to overcome the defences of the larger, slower (often fixed and immobile) nutrient-rich female cell.
The reason the female recipient gamete cell is often either slow-moving or immobilised, is because of its larger size containing nutrient-rich storage of extraneous material in addition to the core DNA – its lack of motility is designed to conserve energy, for the critical task of initial growth of the new offspring organism. This is as true of microscopic bacteria, as it is of fruit trees.
Some plants have more than one ‘sex’, forming 3 or more different gametes, which need to combine to form offspring. A major form of wheat used in human bread is triticale, for it is triploid, ie has 3 sets of chromosomes in its seeds.
In summary, from primordial times, this binary form of reproduction has resulted in very different methods and strategies, for each to maximise its chances of successful offspring.
More about these strategies in Part 2…