There are unicellular organisms that reproduce sexually. Unicellular yeasts can make themselves into a gamete and join their nucleus with a neighbor.
The first ones I remember seeing as a kid was
Paramecium. I had a colony for several years. Conjugation was quite common.
However, sexual reproduction is still a derived feature. The basal characteristic is simple cloning.
One of my favorite organisms when I was a kid were
Hydras. I could find them in almost every scoop with my dipnet, but had to wait to get home and put all the pond scum in a jar or aquarium, before I could see them. They are very simple multicellular organisms that reproduce by cloning or sexually.
From Wikipedia:
quote:
When food is plentiful, many Hydra reproduce asexually by budding. The buds form from the body wall, grow into miniature adults and break away when mature.
When a hydra is well fed, a new bud can form every two days.[10] When conditions are harsh, often before winter or in poor feeding conditions, sexual reproduction occurs in some Hydra. Swellings in the body wall develop into either ovaries or testes. The testes release free-swimming gametes into the water, and these can fertilize the egg in the ovary of another individual. The fertilized eggs secrete a tough outer coating, and, as the adult dies (due to starvation or cold), these resting eggs fall to the bottom of the lake or pond to await better conditions, whereupon they hatch into nymph Hydra. Some Hydra species, like Hydra circumcincta and Hydra viridissima, are hermaphrodites[11] and may produce both testes and ovaries at the same time.
Many members of the Hydrozoa go through a body change from a polyp to an adult form called a medusa, which is usually the life stage where sexual reproduction occurs, but Hydra do not progress beyond the polyp phase.[12]
I often find hydras attached to the exoskeletons of dragonfly nymphs. It's a free ride until the nymph molts.
What if Eleanor Roosevelt had wings? -- Monty PythonOne important characteristic of a theory is that is has survived repeated attempts to falsify it. Contrary to your understanding, all available evidence confirms it. --Subbie
If evolution is shown to be false, it will be at the hands of things that are true, not made up. --percy
The reason that we have the scientific method is because common sense isn't reliable. -- Taq