While President Obama recently lifted the ban on federal funding for embryonic stem cell research imposed by President Bush eight years ago, some people continue to oppose this move and call it unethical. So, while the scientific community is thrilled by the news and says the research will lead to medical breakthroughs, some communities consider the research as a "slippery slope". But, what exactly are stem cells and why are they so important as to generate hot debates among all sorts of circles - political, social, religious, and what not? Here's a look at some of those details.

The science behind stem cells
What sets stem cells apart from other cells is their ability to turn into any other type of tissue in the body. A stem cell from the bone marrow, for example, can be transformed into a neuron or nerve cell in the brain.

Types of stem cells: Embryonic stem cells versus Adult stem cells
Broadly, there are two types of stem cells in humans - embryonic stem cells and non-embryonic stem cells. Embryonic stem cells (ESC), as the name suggests, are isolated from the inner cell mass of an early stage embryo (4-5 days post fertilization, and consisting of 50-150 cells). On the other hand, non-embryonic stem cells which are also known as adult stem cells are found in adult tissues.
Embryonic stem cells are pluripotent as opposed to adult stem cells that are multipotent. What this means is that embryonic stem cells can differentiate into any of the more than 220 cell types in the adult body (to be able to give rise to any mature cell type) while adult stem cells can only form a limited number of cell types (closely related family of cells).

Utility of stem cells
The importance of stem cell lies in the fact that they can be converted into any type of other cells or tissues in the body – neurons, pancreatic tissue, heart muscle cells, etc.
So, for example, stem cells harvested from your bone marrow can possibly be used to repair the damage in your heart muscle caused during a heart attack, or to correct blood disorders such as sickle cell anemia (anaemia) through transfusions of stem cells.
Stem cell therapy is believed to have the potential to dramatically change the treatment of human disease. Embryonic stem (ES) cell therapies have been proposed for regenerative medicine and tissue replacement after injury or disease.
But, it should be noted at this point that embryonic stem cell therapies are not in use yet. They are still only in the stage where medical researchers are testing them on animals.
On the other hand, adult stem cells have been successfully used to treat leukemia (leukaemia) and related bone/blood cancers utilizing bone marrow transplants.

The controversy
The controversy behind stem cell research pertains only to human embryonic stem cell research and not all stem cell research. What is controversial is the fact that the source of the research material, human embryos, is destroyed in the process of harvesting the stem cells. Pro-life activists oppose the research arguing that a human embryo is a human life that is entitled to protection.
Another area of controversy is that embryonic stem cell technologies are a slippery slope that may lead to reproductive cloning which may devalue human life.
The production of adult stem cells, on the other hand, does not require the destruction of an embryo and therefore, adult stem cell research and therapy are not as controversial. Though, adult stem cell treatment does carry a risk of rejection by the body’s immune system.

The present state of stem cell research
There are some countries that offer treatments using stem cells (read about medical tourism) but in such therapies only adult stem cells derived from the patient's body are used (autograft). When possible, autografts are preferred as they remove the risk of rejection by the recipient’s body.
There is promising research ongoing in the field of stem cells to derive treatments for a wider variety of diseases including cancer, Parkinson's disease, spinal cord injuries, diabetes, heart disease, Alzheimer’s disease, Amyotrophic lateral sclerosis or ALS (Lou Gehrig’s disease), multiple sclerosis, lung disease, arthritis, organ failure, and muscle damage, amongst a number of other impairments and conditions.

The future
The ultimate question on the minds of many is – "Why can't we simply use adult stem cells instead of harvesting embryonic stem cells?"
Theoretically, embryonic stem cells are considered better because they work as a biological blank slate and are the most versatile of all stem cells whereas adult stem cells are sort of semi-specialized cells and are not as versatile as ESCs.
Though the field of adult stem cells is not marred by controversies, the problem with adult stem cells is also that they are often present only in minute quantities, are difficult to isolate and purify, and their numbers may decrease with age, according to a primer by the National Institutes of Health (NIH).
At this juncture, much remains unknown about the potential of embryonic stem cells. But, going by the success in the field of animal testing it may very well turn out that embryonic stem cells could provide solutions to many diseases in humans.
The answer to the potential benefits of ESC lies in research. To understand the benefits of embryonic stem cells or any type of stem cells for that matter, and to discover possible treatments in humans, various lines of research need to be pursued simultaneously.
Only research can prove if adult stem cells are better over embryonic stems cells for curing human diseases or vice versa. It may also emerge that adult stem cells offer good treatments for certain ailments, while embryonic stem cells are better for curing others.