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38 votes
Accepted

How did the cardiovascular system evolve?

While others have addressed the big picture aspects of your question, I think it would be useful to look at the specifics. Have a look at the heart (or more accurately, the hearts) of the earthworm: ...
user151841's user avatar
  • 1,397
34 votes
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Is atmospheric nitrogen chemically necessary for life?

To get soil nitrogen in the first place, nitrogen fixation is necessary which takes atmospheric N2 and converts it into biologically useful forms. Nitrogen fixation is performed by bacteria and ...
Bryan Krause's user avatar
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12 votes

How did the cardiovascular system evolve?

This kind of question was raised in a book called "Darwin's Black Box" by Michael Behe, who is a biochemistry professor in the U.S. - he calls this 'irreducible complexity' (IC). For example, the ...
gilleain's user avatar
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11 votes
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Why don't we see life form again and over again?

The first life was probably so fragile and simple we would likely not even recognise it if it did appear. We don't know exactly how, or where, life first appeared but nearly all theories suggest ...
Jack Aidley's user avatar
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10 votes
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Are all cells organisms?

Your friend is incorrect. From Wikipedia: The word organism may broadly be defined as an assembly of molecules functioning as a more or less stable whole that exhibits the properties of life. (...
MattDMo's user avatar
  • 15.3k
9 votes

Lifeless Lake in Siberia

https://www.researchgate.net/publication/200464654 This is a detailed comparison between two lakes in the Trans-Volga region in Russia, one of them being Lake Pustoye. I'm not sure if the Lake ...
Tim D's user avatar
  • 99
9 votes
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Star-like organism seen in microscope

It may be a stellate trichome from a plant. You can find other ones by taking swabs from the onion and nearby plants. cool images here wiki info about trichomes
bandybabboon's user avatar
  • 10.4k
6 votes

Do immortal organisms exist?

The immortal jellyfish (Turritopsis dohrnii) is capable of biological immortality. It's one of few known species capable of reverting completely to a sexually immature, colonial polyp stage after ...
theforestecologist's user avatar
6 votes

How did the cardiovascular system evolve?

This is a good question, but it has a vast scope, as you're talking about the progression of millions of different living animals over hundreds of millions of years, none of which are still alive, so ...
Dan Bryant's user avatar
6 votes

Is designing alien life still just science fiction?

First, you can check out this Wikipedia entry: Hypothetical Types of Biochemistry. I caution you that the scientific utility of many of these hypotheses isn't great since they are, at least currently, ...
canadianer's user avatar
  • 17.7k
5 votes
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Are seedless fruits considered life?

Definition of life The definition of what is alive and what is not is not a matter of biology but a matter of philosophy. Most definitions are based on: Physiology Existence of a metabolism ...
Remi.b's user avatar
  • 68.1k
5 votes

Are viruses self-propelled?

The existing answers are correct. However, there is now one example of a self-propelled† virus. Herpesviruses assimilate kinesin to produce motorized viral particles Here, using herpes simplex virus ...
acvill's user avatar
  • 8,286
5 votes

Is designing alien life still just science fiction?

The answer to this question can go as far as anybody's imaginations. So I'll just tell why the answer is what it is, and try to include scientific facts (possibly with references) wherever possible. ...
another 'Homo sapien''s user avatar
4 votes

Do immortal organisms exist?

Examples found in plant world also- especially those with high vegetative reproduction and regeneration property. https://en.wikipedia.org/wiki/The_Great_Banyan Great banyan tree in Indian botanic ...
Always Confused's user avatar
4 votes
Accepted

Could a single cell be brought to life?

There are species where cells and even whole organisms can go into a state called cryptobiosis where their metabolism is suspended but can be revived later. This usually happens when the conditions ...
Thawn's user avatar
  • 1,239
4 votes

Are seedless fruits considered life?

Yes, they are considered life Seedless fruits can develop in one of two ways: either the fruit develops without fertilization (parthenocarpy), or pollination triggers fruit development, but the ...
Ebbinghaus's user avatar
  • 2,603
4 votes

Which biological kingdom comprises the greatest biomass on Earth?

Probably Eukaryotes. Specifically, plants. This is a very fundamental question of life that is often overlooked. It goes without saying that plants and animals are the strongest contenders. However ...
James's user avatar
  • 11.3k
4 votes

Is designing alien life still just science fiction?

Is there a biological field for designing life? The field is called synthetic biology. It is a very new field. With not many player. Currently being constructed is a synthetic yeast Sc2.0. There is ...
JayCkat's user avatar
  • 2,926
4 votes

Why has life evolved around oxygen?

I think you need to consider that oxygen is toxic to large groups of microorganisms, because it poisons their electron transport chains. Strict anaerobes does not tolerate the presence of oxygen at ...
Jeppe Nielsen's user avatar
4 votes
Accepted

Why do living things go belly up as they die?

limbs are light weight compared to bodies, if you knock an animal around (and it has no active correction AKA is not alive) it will tend to end up on its back just due to where its center of gravity ...
John's user avatar
  • 14.6k
4 votes

How is mankind important to nature?

The classical division of humans and animals has always been self-centered and artificial. Humans are animals, competing with other organisms under exactly the same rules. Evolution involves trade-...
Karl Kjer's user avatar
  • 7,657
4 votes

Why are there not two trees of life?

The emergence of life out of matter is a very rare event. The chance of having such event occurring more than once in a small time-frame is very little. If the time-frame is large enough, then "New ...
alec_djinn's user avatar
  • 3,098
4 votes

Why are there not two trees of life?

...all living things can trace their ancestors back through a multi-branched tree of life, to this first living thing. I don't know exactly how anyone can claim that life arose on this planet only ...
anongoodnurse's user avatar
4 votes

Why are there not two trees of life?

Molecular phylogenetics, among other lines of evidence, strongly suggests that all extant life shares a universal common ancestor. However, this analysis is confounded by horizontal gene transfer. The ...
canadianer's user avatar
  • 17.7k
4 votes

Understanding why the definition of life is so challenging

I have to say that this question is really why I love learning about biology. Despite all of our progress, there are still mysteries and still disagreements on fundamentals. I suspect that as we ...
Larry Freeman's user avatar
3 votes

How did the cardiovascular system evolve?

Simpler forms developed to handle simpler requirements. Take planarians, for instance, which are thin and small enough that they can receive their oxygen supply by diffusion straight through their ...
Harris's user avatar
  • 324
3 votes

Which are the last cells of the human body to die?

They found live skeletal muscle stem cells in human corpses 17 days after death (LiveScience, 2012). They isolated live stem cells from the bone marrow from human fingers 5 days after death and ...
Jan's user avatar
  • 8,059
3 votes

Why does evolution not make our life longer?

I am assuming that by longer life, you mean slower aging, because evolution can do little if a mountain falls on a person! So, why don’t organisms have slower, or better, zero rate of aging? The ...
Prem's user avatar
  • 280
3 votes

Are viruses self-propelled?

The term self-propelled requires some finer qualification in the case of bacteriophages. Although bacteriophages are generally carried via Brownian motion, as described in the other answers, in some ...
Roger V.'s user avatar
  • 3,842

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